Table of Contents. Table of Contents

Transcription

1 Table of Contents Table of Contents Matter and Its Properties... 1 Physical Properties... 5 Matter on the Move: Representing matter in its gaseous, liquid, and solid states... 6 Phase Change Poppers: Investigating sublimation... 6 Cloud in a Bottle: Creating condensation with pressure... 6 Chilly Cans: What causes frost to form on the outside of a cold container?... 6 Invisible Mass: Quick proof that air has mass... 6 It s a Gas: Gasses take up space and exert pressure... 6 Macro vs. Micro: Observing the Tiny Properties of Matter... 6 Slime Time: Investigating the odd properties of non Newtonian fluids... 6 Density... 5 Mystery Box: Watching Ping Pong balls rise to the top... 6 Stacking Colors: Stacking liquids of various densities... 6 Density Blocks: Observing the relationship between mass and volume... 6 Floating Golf Ball: What makes a golf ball float in water?... 6 Hot and Cold Density: Investigating the effect of temperature on density... 6 Mixtures... 5 All Mixed Up: How do you separate elements of a mixture?... 6 Chemical Reactions... 5 Basic Reactions: Investigating color change with acids and bases... 6 Exothermic vs. Endothermic: Reactions that produce and consume heat... 6 Energy... 1 Mechanical Energy... 5 Extra Bounce: Conservation of momentum changes the way balls bounce... 6 Comeback Can: Kinetic and potential energy work together in this tricky can... 6 Heat... 5 Burning Calories: What is a calorie?... 6 Some Like It Hot: Experimenting with three methods of heat transfer... 6 Electricity... 5 i

2 Table of Contents Van de Graaff Generator: A hair raising static electricity experience!... 6 Fun with Static Electricity: Experiments with static electricity... 6 Human Battery: Can the human body conduct electricity?... 6 Currently Working: Test which solutions can conduct electricity... 6 Homemade Motor: A simple motor you can re create at home... 6 Conductor or Insulator?: Find out which materials can and cannot conduct electricity... 6 Light... 5 Bubble Trouble: How does a bubble form? You ll have to go inside one to find out!... 6 Color Combinations: How many colors can you make?... 6 Laser Light Show: Step into the dark room to observe the properties of light... 6 Light Fountain: Create an optical fiber with a stream of water... 6 Why is the Sky Purple?: You ll find out using a special sunset egg... 6 Flying Mirror: Trick your friends into thinking you can fly!... 6 Super Spectroscopes: Learn about spectroscopes and make one to take home... 6 Sound... 5 Catch the Wave!: Is sound the same in different media?... 6 Musical Coat Hangers: A concert only you can hear... 6 Good Vibrations: Visualize sound waves... 6 Better Vibrations: Watch what happens when a tray of salt meets a speaker... 6 Forces and Motion... 1 Direction and Speed... 5 Hovercraft: Discover Newton s Laws while hovering... 6 Let s Do the Swivel: Investigating angular momentum... 6 Bull s Eye!: Try and land the rover on mars!... 6 Physics Fear Factor: The conversion from potential to kinetic energy... 6 Magnetism... 5 Magnet Mania!: Learn how magnets work and make your own compass... 6 Eddy Currents: Discover how magnets affect the speed of equipment... 6 Gravity... 5 How Does This Stack Up?: Try to defy gravity with blocks... 6 Loony Balloons: Investigate the strange trajectory of this balloon... 6 Gravity Keeps You Down: How does the force of gravity affect different objects?... 6 ii

3 Table of Contents Spinning the Bucket: Centripetal force will keep you dry... 6 Audible Acceleration: Hear the force of gravity... 6 Air Pressure... 5 Mystery Candle: create a vacuum and see the magic!... 6 Balloon in a Bottle: See how air can take up space... 6 The Power of Words: Atmospheric pressure is a surprisingly strong force... 6 Automatic Balloon Inflator: See how temperature affects air... 6 Magic Playing Card: See how air pressure holds up water... 6 Friction... 5 Friction: See how friction can slow objects down... 6 Surface Tension... 5 H 2 Olympics: Compete using adhesion and cohesion!... 6 iii

4 Table of Contents iiii

5 Matter and Its Properties Matter on the Move Passport Question: What are the three phases of matter? Materials: 3 plastic plates Approximately 50 marbles (depending on the size of the plates) Intro: It is hard to imagine that matter is made of particles since it is impossible to see them. In this activity, we will show how molecules behave when they are in solid, liquid, and gaseous states. Setup: Label the 3 plastic plates solid, liquid, gas Fill the solid plate with marbles until there is almost no room between them. Fill the liquid plate with fewer marbles, so that they can roll around a bit. Fill the gas plates with even fewer marbles, giving them room to move freely. Procedure: 1. Have the students examine the relative space between the marbles on the three plates. How do the marbles move differently? Explain that this represents how atoms move in matter when it is in each of the three phases. Passport Answer: Solid, Liquid, Gas 1

6 Matter and Its Properties 2

7 Matter and Its Properties Phase Change Poppers Passport Question: What is the phase change when a solid becomes a gas? Supplies: Safety Goggles Tall Airborne container Dry Ice Mortar and Pestle Screwdriver Cooler Plastic Spoon Beaker Ice Cost: $15-20 total Background: Dry Ice is the solid form of carbon dioxide, a normal part of our earth's atmosphere. Carbon dioxide is the gas that we exhale during breathing and the gas that plants use in photosynthesis. It is also the same gas commonly added to water to make soda water. Dry Ice is particularly useful for freezing, and keeping things frozen because of its very cold temperature: F or C. Dry Ice is widely used because it is simple to freeze and easy to handle using insulated gloves. Handling it without insulated gloves can cause frostbite. Dry Ice changes directly from a solid to a gas in normal atmospheric conditions through a process called sublimation. This is why it gets the name "dry ice." The opposite process, which changes carbon dioxide from a gas to a solid, is called deposition. Dry ice is easily manufactured. First, gases with a high concentration of carbon dioxide are produced. Such gases can be a byproduct of another process, such as producing ammonia from nitrogen and natural gas, or large-scale fermentation. Second, the carbon dioxide-rich gas is pressurized and refrigerated until it liquefies. Next, the pressure is reduced. As a result, some liquid carbon dioxide vaporizes, causing a rapid lowering of temperature of the remaining liquid. The extreme cold causes the liquid to solidify into a snow-like consistency. Finally, the snow-like solid carbon dioxide is compressed into either small pellets or larger blocks of dry ice. As a general rule, Dry Ice will sublimate at a rate of five to ten pounds every 24 hours in a typical ice chest. Dry Ice sublimates faster than regular ice melts but will extend the life of regular ice. Commercial shippers of perishables often use dry ice even for non frozen goods. Dry ice gives more than twice the cooling energy per pound of weight and three times the cooling energy per volume than regular water ice (H₂O). It is often mixed with regular ice to save shipping weight and extend the cooling energy of water ice. Sometimes dry ice is made on the spot from liquid 3

8 Matter and Its Properties CO₂. The resulting dry ice snow is packed in the top of a shipping container offering extended cooling without electrical refrigeration equipment and connections. Experiment procedure: 1. Put a small amount of crushed dry ice in one Erlenmeyer flask. Place water ice in a second Erlenmeyer flask. Have students discuss their observations. 2. Have everyone wear safety goggles. 3. Crush a small amount of dry ice with the mortar and pestle. 4. Using a spoon take a small amount of dry ice from the mortar and pestle and put it in the Airborne container. 5. Making sure that the top of the container is pointed directly at the ceiling, place the lid on the container. Hold the container with one hand. Fire in the hole Discussion: 1. What are the three states of matter? SOLID LIQUID GAS 2. How does matter achieve various states and how does this relate to the process of phase changes? Matter changes as a result of heating and cooling. This vocabulary explains the various phase changes. Freezing: Liquid to Solid (Cooling) Melting: Solid to Liquid (Heating) Evaporation: Liquid to Gas (Heating) Condensation: Gas to Liquid (Cooling) Sublimation: Solid to Gas (Heating) Deposition: Gas to Solid (Cooling) 3. Ask the students whether they can explain why the lid launched off of the container. Discuss. When dry ice sublimates, it expands. The mass stays the same, but the volume increases. Passport Answer: Sublimation 4

9 Matter and Its Properties Cloud in a Bottle Passport Question: What two processes form clouds? Supplies: 1-liter clear plastic bottle with cap Foot pump with rubber stopper attached Water Rubbing alcohol Safety goggles Cost: $5-$10 total Background: A cloud is a visible mass of liquid droplets made of water, suspended in the atmosphere above the earth s surface. They are formed by two processes: cooling the air or adding water vapor to the air. Often times, these processes are acting together to form clouds. There are several different types of clouds, named by their shape, altitude (height in the atmosphere), and density. These Latin roots are used to indicate the shape and density, with prefixes occasionally used to indicate altitude: Latin Root Translation Example cumulus stratus cirrus nimbus heap layer curl of hair rain fair weather cumulus altostratus cirrus cumulonimbus Cumulus clouds are the big, fluffy type, stratus appear in layered sheets, cirrus take the form of thin wisps, and nimbus are the thick, dark type that often produce precipitation. Intro: Ask the students what they know about clouds. How are they formed? What are they made of? Explain that water molecules are in the air all around us. These airborne water molecules are called water vapor. When the molecules are bouncing around in the atmosphere, they don't normally stick together. Clouds are formed when the water vapor cools and compresses into visible droplets. We ll explain this a bit more after making a cloud of our own! Procedure: 1. Put enough warm water in the bottom of the 1-liter bottle to cover the bottom. 2. Swirl the water around and then put the rubber stopper in the bottle. 5

10 Matter and Its Properties 3. Pump the foot pump 10 times while making sure that the stopper doesn t pop off the top of the bottle. 4. When you are done pumping, pull out the stopper. You should see a cloud form in the bottle. 5. This time, place a few drops of rubbing alcohol in the bottom of the 1-liter bottle. 6. Swirl the alcohol around in the bottle, making sure to coat the sides. Then put the rubber stopper in the bottle. 7. Again, pump the foot pump 10 times while making sure that the stopper doesn t pop off the top of the bottle. 8. When you are done pumping, pull out the stopper. You should see a more visible cloud than you saw with the water. 9. But a bit more alcohol in the bottom of the bottle and try again with pumps. You should see an even more visible cloud. How does it work? Pumping the bottle forces the molecules to squeeze together or compress. Releasing the pressure allows the air to expand, and in doing so, the temperature of the air becomes cooler. This cooling process allows the molecules to stick together - or condense - more easily, forming tiny droplets. Clouds are nothing more than groups of tiny water droplets! The reason the rubbing alcohol forms a more visible cloud is because alcohol evaporates more quickly than water. Alcohol molecules have weaker bonds than water molecules, so they let go of each other more easily. Since there are more evaporated alcohol molecules in the bottle, there are also more molecules able to condense. This is why you can see the alcohol cloud more clearly than the water cloud. Clouds on Earth form when warm air rises and its pressure is reduced. The air expands and cools, and clouds form as the temperature drops below the dew point. Invisible particles in the air in the form of pollution, smoke, dust or even tiny particles of dirt help form a nucleus on which the water molecules can attach. Passport Answer: Cooling of atmospheric air and adding water vapor to air are the two processes that cause clouds to form. 6

11 Matter and Its Properties Chilly Cans Passport Question: Why do water droplets form on the outside of a cold glass? Supplies: Ice Salt Empty Metal Can Metal Spoon Paper Towel Safety Goggles Tablespoon Cost: $10 total Background: Condensation is the phase change of matter from a gaseous phase to a liquid phase. This process occurs naturally in the atmosphere, and is visible when water droplets form on the outside of a cold glass. Condensation even serves some biological purposes in nature. Coastal redwoods, for instance, rely on the condensation of fog as a water source in the summer when the precipitation rate is low. Fog condenses onto the leaves and drips down to the ground near the roots of the tree. This process supplies approximately 15-45% of the total water used annually by redwoods. In this activity, we re taking the process of condensation a step further. We will be condensing water vapor into a liquid form on the outside of metal cans, and allowing it to cool enough to become frost. This is done by cooling the ice water on the inside of the can below the freezing point (32 F/0 C) using salt. Salt lowers the freezing point of water, making the surface of the metal can very cold. Setup: 1. Each student will need enough crushed ice to fill their metal can. Crushed ice works better than cubed ice. 2. Remove the labels from the cans and wash them. 3. Use pliers to carefully down any sharp or jagged edges around the top of each can. Cover the rim of each can with duct tape. Procedure: 1. Ask students if they ve seen liquid form on the outside of a cold glass? What is this called? Condensation. Do they know how this happens? 2. We ve seen liquid form on the outside of a glass, but is it possible to make a solid form? Have the students guess how we will do that. 3. Dry the outside of the metal can with a paper towel. 7

12 Matter and Its Properties 4. Place one heaping tablespoon of salt in the bottom of the can. Fill the can about halfway with crushed ice. 5. Put another heaping tablespoon of salt in the can. Add more ice until the can is almost full. 6. Put in a third tablespoon of salt. 7. Hold the can securely and mix the ice-salt mixture with a sturdy metal spoon for about 1 minute. Remove the spoon, and observe the outside of the can. Do not touch it yet. 8. Wait 3-5 minutes. 9. Look at and touch the outside of the can. Have the students record/discuss their observations. Discussion: 1. Ask students, What do you notice on the outside of the can? Why do you think there was frost on one part of the can and water on another part? 2. Explain how water vapor in the surrounding air can become frost. 3. Stick a thermometer in the ice in the can. After waiting a minute, have students read the temperature. Do they know why it reads below 0 C? Salt lowers the freezing point of ice below 0 C. 4. Explain that this activity can be used as a model of what happens to water vapor in the atmosphere. Tell students that models help us to understand objects or processes that cannot easily be seen. In this model, the can represents the cold temperature in the upper atmosphere and the water vapor in your classroom represents the water vapor in the atmosphere. Ask students to use this activity as a model and explain what the liquid and frost on the outside of the can might represent. 5. Students may suggest that the liquid could be tiny drops of water in clouds or rain and the frost could be tiny ice crystals in clouds or snow. Passport Answer: Condensation. Water vapor in the air cools and condenses on the glass. 8

13 Matter and Its Properties Passport Question: Invisible Mass Supplies: One empty 2-liter bottle One fizzkeeper pump cap One balance (triple-beam recommended) Cost: $5-$10 total Intro: Air is usually invisible, so most of us don t give it much thought at all. In fact, when students are asked about the mass or weight of air, many are perplexed. Air seems like it doesn t have mass, but it does. Ask students, Can you feel the air around you? Do you think it weighs anything? We can measure the mass of air by weighing it before and after pumping air molecules into a bottle. Procedure: 1. Attach a Fizzkeeper cap to a 2 liter bottle. Don t pump any extra air into the bottle. Have students feel the bottle, checking for weight and pressure. 2. Weigh the bottle on a triple beam balance and record your findings. 3. Ask your class to predict what will happen if you pump extra air molecules into the bottle and then measure its mass. 4. Have students use the Fizzkeeper to pump more air molecules into the bottle. They can keep a count of the number of pumps if they like. If you have an accurate balance, students can measure the mass of the bottle as a function of the number of pumps. There is a clear trend, but at some point, the mass will stop increasing as the pump caps can t pump any more air into the bottle. 5. When the pumped bottle is pumped full as it can be, have the students feel the bottle, checking again for weight and pressure. What do they notice? 6. Weigh the bottle on the triple balance beam and compare and discuss your two findings. If there are more molecules in the bottle, there s more pressure and more mass! Discussion: 1. Ask students, Why did the mass increase when we pumped air into the bottle? Because air has mass. Because of this, air is exerting pressure on our bodies all the time. Passport Answer: 9

14 Matter and Its Properties 10

15 Matter and Its Properties It s a Gas Passport Question: When vinegar and baking soda react, what bubbles out of the solution? Supplies: Beaker Small Erlenmeyer flask Large Erlenmeyer flask Water Blue Food coloring Spoonful of baking soda Spoonful of citric acid Tube/stopper setup Cost: $10 total (reusable setup) Background: This activity demonstrates a chemical reaction. Reactants (the original substances that react to each other) are changed during the process, so the end result (the product) is a substance that is chemically different from the two reactants. This differs from a physical change because the products of a chemical reaction cannot be easily converted back to the two reactants. In this reaction, vinegar (acetic acid) and baking soda (sodium bicarbonate) react to form carbonic acid and sodium acetate. Because the carbonic acid is unstable, it immediately breaks down into carbon dioxide and water. The fizzing that you see is the carbon dioxide gas bubbling out of the solution. HC 2 H 3 O 2 (aq) + NaHCO 3 (s) --> NaC 2 H 3 O 2 (aq) + CO 2 (g) + H 2 O(l) The second aspect of this experiment is the displacement of a liquid by a gas. When carbon dioxide is produced in the chemical reaction, it exerts pressure on the large flask. Some of that gas flows through the tube into the small flask, which displaces the water. As a result, some water moves through the second tube into the beaker. Procedure: 1. Wear safety goggles. 2. Rinse the large flask. 3. Add 200 ml blue water to the small flask. 4. Assemble the flasks, beaker, and tubing. Put the end of the loose tube in the beaker. 5. Add one teaspoon baking soda to the large flask. Add 50 ml of water. Swirl to mix the contents. 11

16 Matter and Its Properties 6. Add one teaspoon citric acid to the large flask and quickly replace the stopper. Hold the stoppers on both flasks. 7. Notice the bubbling gas produced in the large flask. Where is the gas going? 8. Try adding more citric acid. Does the reaction continue? Discussion: 1. Discuss why the water moved from the flask to the beaker. The chemical reaction of baking soda (C₆H₈O₇) and citric acid (NaHCO₃) and water (H₂O) produces carbon dioxide (CO₂). The gas moves through the tubing into the flask with the water and displaces the water. 2. Explain that gas takes up space and can exert pressure, even if it is not visible. For example, gas pressure inflates a balloon or escapes as fizz when you open a soda. Passport Answer: Carbon dioxide 12

17 Matter and Its Properties Passport Question: What does macro mean? Supplies: Microscope Index Cards Ruler Scissors Scotch Brand invisible tape Salt Sugar Baking Soda Baking Powder White Sand Cost: $10-15 total Macro vs. Micro Background: Some objects appear to be the same or very similar when viewed with the naked eye, but look very different when viewed at greater magnification. By viewing objects like this under a microscope, we can observe the details and properties that differentiate them from each other. In this activity, we will be looking at five white powdery substances with the naked eye, and then doing the same under a microscope. Are they all the same size when viewed up close? What are the similarities and differences between them? Scientists use microscopes for a whole variety of reasons. Here at Lake Tahoe, they are important for viewing very small organisms and particles in the lake. Phytoplankton (algae) and zooplankton are good examples. Some of the zooplankton in the lake are easily seen by the naked eye, like the mysis shrimp, but others are difficult to see in detail without a microscope. What are other things scientists might observe through a microscope? Setup: 1. Prepare the slides by sprinkling a small amount of each of the white powdery substances on a piece of tape. Put another piece of tape on top so that the sticky sides are facing each other. 2. Sprinkle a little of each substance on index cards and set out for students to observe. Don t forget what substance is on each index card! 3. Set up the microscope. Procedure: 1. With the naked eye, have the students observe the macro properties of the white powdery substances provided. Can they guess what the substances are? 13

18 Matter and Its Properties 2. Describe the macro properties of each substance in as much detail as possible. 3. Show the students how to put the slides under the microscope and focus the microscope. 4. Describe the micro properties of the substance that you observe. 5. Have them guess a second time. What could they see with the microscope that they couldn t see with the naked eye? Discussion: 1. Define micro and macro. Macro means big. In this case, when we consider the macro properties of matter, we are only making observations with the unaided eye. Micro means tiny. Scientists use microscopes to observe the tiny properties of matter that cannot be seen with the unaided eye. 2. How do we measure things at the macro level? a. Show that we measure macroscopic things in millimeters (mm), centimeters (cm), and larger units. Demonstrate with an object (i.e. penny, pencil) and the ruler. b. At the microscopic level, we start measuring in micrometers (μm). Ask students what other things can be measured at the micro scale. 3. Have the students compare and contrast each substance at both the macro and micro level. 4. How do the properties/ structures of each substance differ? How are they similar? 5. Do the students understand how to operate the microscope? Can they focus the scope independently? 6. What are things in lake Tahoe that are microscopic? Macroscopic? Passport Answer: Big. Things on the macroscopic scale can be seen with the naked eye. 14

19 Matter and Its Properties Slime Time Passport Question: What type of fluid acts like both a liquid and a solid? Supplies: Newspaper Measuring cups 1 cup cornstarch Large bowl or pan Green Food coloring ½ cup water Cost: $10-$15 total Procedure: 1. Put cornstarch in bowl or pan. 2. Add a drop or two of green food coloring. 3. Add water slowly while mixing. The mixture should be about 2/3 cornstarch, 1/3 water 4. Try different experiments with the ooze. a. Put a small plastic toy on the surface. Does it sink? How does the substance when you press on it quickly? Slowly? b. What happens when you slap your hand or punch your fist into the substance? c. Does it act like a solid or a liquid? When d. Can you roll a small amount of it into a ball? What happens if you set the ball in your hand? e. What happens if you put just a tiny amount between your fingers and then rub your fingers together? f. What can you do to allow this substance to act like a liquid? What can you do to make this substance act like a solid? Lesson: Oobleck slime is a suspension (a liquid containing small solid particles that easily separate out of the mixture) of cornstarch and water. This substance has, under certain conditions, the properties of both a liquid and a solid. It is called a non-newtonian liquid because sometimes it doesn t behave like a liquid should, according to Isaac Newton s laws. When struck, most liquids splatter and splash. However, when a non-newtonian liquid is struck by a force, the physical structure of the material changes, increasing the thickness of the solution, making it behave more like a solid. Passport Answer: A non-newtonian fluid. 15

20 Matter and Its Properties 16

21 Matter and Its Properties Density: Passport Question: What is the density of fresh water? Background: The density of a material is its mass per unit volume. Mathematically, density (ρ) is defined as mass (m) divided by volume (V): ρ=m/v. Another way to conceptualize this is by thinking of how packed together the molecules of a material are. In general, density can be increased or decreased by changing either the pressure or the temperature. Increasing the pressure always increases the density of a material. Increasing the temperature generally decreases the density, but there are notable exceptions to this generalization. For example, the density of water increases between its melting point at 0 C and 4 C; similar behavior is observed in silicon at low temperatures. Pressure has a much stronger effect on the density of gasses than on the density of solids or liquids. Bean Box Supplies: Three ping-pong balls Two or three metal balls (same size as ping-pong balls) Bag of pinto beans Large mixing bowl Cost: $20 total Procedure: 1. Pour the beans into the bowl. 2. Bury the ping-pong balls under the beans and lay the metal balls on top. 3. Ask students, What do you think will happen if we shake the bowl? 4. Gently shake the bowl. The metal balls will sink to the bottom and the ping-pong balls will rise to the top. Discussion: 1. What happened to the metal balls? To the ping-pong balls? 2. Take out one of each item and pass around to the students. What do you notice about these three items? 3. Introduce the concept of density. An object s density is its mass divided by its volume. sdjanother way to think of this is how packed together the molecules in an object are. Of the three objects we experimented with, the metal ball has the highest density, the pingpong ball has the lowest density, and the pinto bean is somewhere in between. As a result, the metal balls sink to the bottom of the bowl and the ping-pong balls float up. 4. Can the students think of three other objects that we could do the same experiment with? 17

22 Matter and Its Properties Density Column Supplies: Small graduated cylinders Pipettes Karo syrup Colored dish soap Water Vegetable oil Rubbing alcohol Lamp oil 6 beakers Scale Handheld calculators Cost: $30-$40 total Setup: 1. Pour an equal amount of each liquid into one of the 6 beakers. Label each beaker with its liquid by taping a small sign to the beaker. 2. Set out the small graduated cylinders and pipettes. Each student should have one of each for the investigation. Procedure: 1. Tell the students that they ll be trying to stack the liquids on top of each other in their graduated cylinders (having learned what densityy is in the previous demo.) 2. Ask them, how should we arrange the liquids in the cylinder so that they stack on top of each other? They should be stacked from lowestt density to highest density. Explain that liquids of different densities won t mix as long as the liquid with the lower density is sitting on top of the liquid with the higher density. 3. Give each student a pipette and a graduated cylinder. They will try to stack the liquids in order from lowest density to highest density by guessing the correct order. Dry not to let the liquids drip on the table! They can get messy and sticky. 4. After they have put all six liquids in their cylinder,, observe the results. Did any students guess them all in the correct order? What happened to the liquids if they guessed in the wrong order? 5. If none of the students put all six liquids in the correct order, demonstrate for them. Discussion: 1. How did students determine which liquids were most dense? Did they pick up the beakers to test the weight of each liquid? Did they tilt the beakers to test viscosity? Liquids that are more dense will have a higher viscosity than liquids that are less dense. 18

23 Matter and Its Properties 2. The same volume of two different liquids will have different weights because they have different masses. Put each beaker of liquid on the scale to show this. 3. Measure the density of each of the liquids with the students using the equation density=mass/volume. To do this, put a graduated cylinder with 10 ml of a liquid on the scale. Write down the mass. Subtract the mass of an empty graduated cylinder. Divide the mass of the liquid by 10 ml (the volume). The product of this equation is the density of that liquid. 4. Write down the results to show that the six liquids in the column are ranked in order of increasing density. If this takes too much time, just calculate density for a couple of the liquids. 5. Can the students think of other liquids that are very dense? (honey, molasses) Can they think of some liquids that are less dense? Density Blocks Supplies: Set of 12 density blocks Clear bowl filled with water Scales Handheld calculators Cost: Free (we already have a set of density blocks) Intro: Now that we ve looked the density of several liquids, we re going to observe and measure the density of solid objects. During this activity, students will put different blocks in water to see which float and calculate the density of the blocks using a scale and a calculator. Objects that float in water will have a density less than 1 g/cm³ (density of water) and objects that sink will have a density greater than 1 g/cm³. Procedure: 1. Give students a couple minutes to experiment with the objects, test which ones float in the bowl of water, compare the weight of two blocks by holding one in each hand, etc. 2. Measure the density of a few of the blocks. Put a block on the scale, record the mass. 3. Divide mass by the volume of the cube (1 in³= cm³). The result is the density. Record this on the laminated density sheet. Discussion: 1. Do the students understand how to measure density of a solid? 2. Were the students surprised by any of the results? Passport Answer: 1 mg/l 19

24 Matter and Its Properties 20

25 Matter and Its Properties Floating Golf Ball Passport Question: Which is more dense, freshwater or saltwater? Supplies: 16 oz plastic cups (10) Salt (20 lbs) Plastic spoonss (10) Water Water pitcher Golf balls (13) Dump bucket Beaker (3) Cost: $20 total Setup: Fill the three beakers 2/3 full with water. Place one golf ball in each. Leave one alone (the golf ball will sink to the bottom), Put enough salt in the second so that the golf ball hovers in the middle of the water, and put even more salt in the third so the golf ball floats on the water. These will be set out as a demonstration. You may have to occasionally stir the second two beakers to keep the salt in suspension. Procedure: 1. Pass out a plastic cup and a spoon to each student. 2. Fill the cups 2/3 full with water. 3. Have the students make a prediction: Will the ball sink or float when it is placed in the water? 4. Test the hypothesis. Place the golf ball in the water. It will sink to the bottom of the cup. 5. Talk to the students about changing the density of f water using salt. By adding salt, we will increase the density of the solution. Will this make a difference? 6. Add a significant amount of salt to each student s cup and have them stir. Is it floating yet? If not, keep adding it and stirring. Eventuallyy the ball will float. Discussion: 1. Why doesn t the ball float in fresh water? Initially, the golf ball is denser than the water, so it sinks to the bottom. 2. Ask the students to explain why the ball floats in the salt water. On a molecular level, the salt is filling in the microscopic spacess that exist between water molecules; this process packs the atoms that make up the solution together, which increases the density of the solution to the point that it is greater than the density of the golf ball. 21

26 Matter and Its Properties 3. This is similar to what you experience when swimming in salt water. Ask the students if they ve ever tried swimming in the ocean. Unlike when swimming in a pool, they can float almost effortlessly. Passport Answer: Saltwater 22

27 Matter and Its Properties Hot and Cold Density Passport Question: How can you change the density of water? Supplies: Room-temperature water Hot water Cold water 10 Droppers 10 Clear plastic cups 10 Small cups Yellow and blue food coloring Water-resistant card (a laminated index card will do) 2 Small jars (must have the same-sized opening) Coffee stirrer, straw, or spoon Paper towels Safety goggles Cost: $10-$20 total Setup: 1. Label half of the small cups hot water and the other half cold water. 2. Put a drop of yellow food coloring in the hot water cups and a drop of blue food coloring in the cold water cups. 3. Immediately before distributing to students, place two tablespoons of very hot and very cold water into the labeled cups. Procedure: 1. Instruct students to put on safety goggles. 2. Discuss with students their ideas about whether heating and cooling can have an effect on the density of a substance. Has anyone ever noticed that the water at the bottom of a lake feels colder than water at the surface? Maybe different temperatures of water can have different densities and form layers. 3. Test this by having the students put hot and cold water into room temperature water. a. Fill 2 clear plastic cups about 2/3 of the way with room-temperature water. b. Fill one dropper with cold water colored blue. Poke the end of the dropper a little beneath the surface of the colorless room-temperature water. While observing from the side, gently squeeze the dropper so that the cold water slowly flows into the room-temperature water. c. Fill another dropper with hot water colored yellow. Poke the end of the dropper a little beneath the surface of the room-temperature water. While observing from the side, gently squeeze the dropper so that the hot water slowly flows into the roomtemperature water. 23

28 Matter and Its Properties d. In a separate cup of room temperature water, push a dropper filled with hot yellow water to the bottom of the cup. While observing from the side, gently squeeze so that the hot water slowly flows into the room temperature water. e. Push a dropper filled with cold blue water to the bottom of the cup. While observing from the side, gently squeeze so that the cold water slowly flows into the room-temperature water. f. In both cups, the hot water should collect at the top of the cup and the cold water should collect at the bottom. 4. Discuss student observations. a. What does your experiment say about the relative densities of hot, roomtemperature, and cold water? b. Based on your observations, wo7uld you expect equal volumes of hot, roomtemperature, and cold water to weigh the same? c. Which temperature of water would you expect to weigh the most? The least? 5. Do a demonstration to highlight the difference in density between hot and cold water. Tell students that you are going to try to place one jar filled with colored water upside-down over another one and that you want the colors to stay separate. Ask students if you should use hot and cold water to do this, or if the temperature of the water doesn t matter. Ask: Which temperature should be on top, and which on the bottom to keep the colors separate? a. Completely fill a baby food jar with hot tap water and 2 drops of yellow food coloring. b. Completely fill another baby food jar with very cold water and add 2 drops of blue food coloring. Stir the water in both jars so that the coloring is well-mixed in both. Place the cold water jar on a paper towel. c. Hold a water-resistant card, like a playing card or a laminated index card, over the top of the hot-water jar. d. While holding the card against the jar opening, carefully turn the jar upside down. e. With the card still in place, position the jar of hot water directly over the jar of cold water so that the tops are lined up exactly. f. Slowly and carefully remove the card so that the hot water jar sits directly on top of the cold water jar. The hot water should, for the most part, sit on top of the cold water. Discussion: 1. Ask the students what they think would happen if you placed the cold blue water on top of the hot yellow water and then removed the card. 2. Relate hot water and cold water to lake mixing. When the water on the top of the lake is warmer than the water at depth, the lake does not mix very much. This is often the case in warmer months because the sunlight warms the top layers of water, but does not reach the depths of the lake. When the air is very cold in winter and cools the surface of the lake, the cold water sinks to the depths and causes the lake to mix. Passport Answer: You can change the density of water by changing its temperature. 24

29 Matter and Its Properties All Mixed Up Passport Question: Are mixtures separated by chemical or by physical means? Supplies: 2 cups small pebbles 1-2 cups small plastic beads 1 cup paper clips 1 magnet One large Ziploc bag 1 plastic tablespoon ml beakers One small kitchen strainer (to fit over the beakers) One stirrer 1 plastic bucket for waste 1 small net Cost: $10-$15 total Intro: Chemists often separate substances by their different properties or characteristics. Plastic beads, water, and stones have different densities. Substances with a lower density than water, such as plastic beads, float on water, objects with a greater density than water, such as pebbles, sink. Many substances, like salt, dissolve in water, while others, like plastic beads, pebbles, and paper clips, do not. If you heat salt-water or leave it in the sun, the water evaporates, leaving solid salt behind. Some objects, like paper clips, can be pulled out of mixtures using their magnetic properties. A similar method to the one used in this experiment is used at many recycling facilities to separate materials. Previously it was necessary to separate all recycled materials at home before pickup, but now many can be mixed together and separated at the recycling center. Magnets can be used to separate many metals; water can separate materials with a higher density from those of a lower density. Setup: 1. Pour roughly 300 ml water into a jar or beaker. 2. Labe the three 400-ml beakers Beaker 1, Beaker 2, and Mixture. 3. Label the plastic bucket Waste. 4. Label the petri dish Water from beaker 2 left in the sun for one day. 5. Prepare mixture : combine equal parts small pebbles, small plastic beads, and paper clips. Procedure: 1. Always wear safety goggles. 25

30 Matter and Its Properties 2. Put a scoop of mixture into beaker Have the students look into the beaker and find all three parts: small rocks, plastic beads, and paper clips. 4. Add 300 ml water to the mixture in beaker 1. Use a spoon to mix the contents. 5. Let the beaker sit for a few moments. Ask students: Where are the pebbles, plastic beads and paper clips now? 6. Separate the mixture using the following steps: a. The plastic beads will float because they have a lower density than water, so scoop them out with the net. b. Set the strainer over beaker 2. c. Carefully pour the wet mixture in beaker 1 through the strainer into beaker 2. d. Separate the paper clips from the pebbles by picking the paper clips up with the magnet. e. Take the strainer off beaker 2. Ask: Where are the pebbles, plastic beads, and paper clips now? Discussion: 1. What properties helped you separate stones, beads, and paper clips? 2. Explain that all of these objects are part of a mixture because they are not chemically joined together they can be separated by physical means. 3. Explain that chemists spend much of their time separating mixtures and solutions. Can the students think of real life examples? (Separating oil from water after an oil spill, removing environmental contaminants). Passport Answer: Physical. 26

31 Matter and Its Properties A Basic Reaction Passport Question: Name one indicator of a chemical reaction. Supplies: Turmeric powder Safety goggles Rubbing alcohol Calcium chloride Baking soda ml beakers Plastic spoons Approximately 20 Plastic cups 5 pop-top squeeze bottles ml graduated cylinders Cost: $15-$20 total Intro: In this activity, students will investigate simple chemical reactions with easily observable changes. The most common signs of chemical reactions include the following: Production of a gas, solid, or liquid Change in temperature Appearance of light Change in color Change in ph Production of electricity The first part of this experiment causes a change in color. The turmeric powder is an acid/base indicator. When it reacts with baking soda (a base), it turns red. When calcium chloride is added, the baking soda and calcium chloride react to produce carbon dioxide (a gas). Calcium chloride is an acid, so the turmeric changes back to yellow. Also, heat is produced in this reaction, so it is an exothermic reaction. When a reaction takes up heat, making it feel colder, it is endothermic. Setup: 1. Dilute rubbing alcohol solution in a pop-top squeeze bottle. a. For 70% rubbing alcohol, mix 1 part rubbing alcohol to 1 part water (35% solution.) b. For 90% alcohol, mix 1 part isopropyl alcohol to 2 parts water (30% solution). 2. Fill a beaker with baking soda. Label the beaker baking soda. 3. Fill a beaker with turmeric powder. Label the beaker turmeric. 4. Fill a beaker with calcium chloride. Label the beaker calcium chloride. 27

32 Matter and Its Properties Procedure: 1. Have students measure 25 ml of alcohol using the graduated cylinders, and then pour the alcohol into a plastic cup. 2. Add 1 spoonful of baking soda into the same plastic cup. 3. Mix the baking soda and alcohol with the plastic spoon until the baking soda dissolves. 4. Dry the spoon with a paper towel. 5. Add a pea-sized amount of turmeric powder. Mix the contents of the cup for seconds. What do the contents look like? 6. The contents of the cup should have turned red. Discuss with the students that color change is an indication of a chemical reaction. 7. Put one heaping spoonful of calcium chloride into the same plastic cup. Mix the contents for seconds. a. Do you notice any changes occurring? b. What do you feel, hear, and see? c. What evidence is there of a chemical reaction? Discussion: 1. What did the chemicals look like before you mixed them in the cup? The baking soda was a white powder. The turmeric was yellow and the alcohol solution was clear. The mixture of baking soda with turmeric is red. 2. How was the mixture different after you added the calcium chloride? What did you see, hear, and feel? It turned yellow; it got hot/warm; the bag filled up with air; bubbles appeared; it got foamy, etc. 3. Are any of those observations indicators of a chemical reaction? Yes, all of them; color change, production of a gas, temperature change. 4. How do you know that a gas was produced? How many color changes did you observe? There are two color changes one when the yellow turmeric powder was added to the baking soda and turned red, and again when the calcium chloride was added and the solution turned yellow. In each case, the turmeric detected a base (baking soda) or an acid (carbon dioxide gas). Passport Answer: Calcium Chloride 28

33 Matter and Its Properties Exothermic vs. Endothermic Passport Question: What compound is used to melt ice and snow on roads? Supplies: Two 250-ml Erlenmeyer flasks Two 1-tsp measuring spoons Two small plastic funnels ml beakers One 25-ml graduated cylinder Calcium chloride pellets Urea Two colors of masking tape Cost: $25-$30 total Intro: In this activity, students will learn that some reactions release energy in the form of heat and others absorb energy, making their surroundings colder. There are practical uses for these kinds of chemical reactions. Calcium chloride, for instance, produces heat when it reacts with water. This is why it is used in deicers; it melts snow or ice. In more detail, exothermic reactions produce heat because energy is produced when chemical bonds are broken and formed. Endothermic reactions absorb heat while breaking and forming new bonds, which is why they cause their surroundings to feel colder. Setup: 1. Label 250-ml squirt bottle Water 2. Using one color of tape, label a flask, a funnel, a teaspoon, and a beaker Calcium Choloride. 3. Using the other color of tape, label a flask, a funnel, a teaspoon, and a beaker Urea. Procedure: 1. Always wear safety goggles. 2. Use the graduated cylinder to pour 15 ml of H₂O into each flask. 3. Use the funnel to add 1 teaspoon urea to the flask marked urea, and 1 teaspoon calcium chloride to the flask marked calcium chloride. 4. Swirl both flasks 5-10 times. 5. Touch the bottoms of the flasks to feel temperature changes. a. Which reaction is warm, or exothermic? (Calcium chloride) b. Which reaction is cold, or endothermic? (Urea) 6. When finished, empty both flasks and rinse with water. 29

34 Matter and Its Properties Discussion: 1. Ask students: which of these chemicals do you think is sprayed onto airplane wings to melt ice? Calcium chloride. 2. Which of these chemicals works like the chemical used in first aid instant cold packs? Urea. 3. Do the students understand the difference between exothermic and endothermic? Passport Answer: Production of light, production of a gas, temperature change, color change. Change to: 30

35 Energy Extra Bounce Background: What are we talking about when we talk about energy? In physics, energy is the capacity to do work. Work is done whenever an object is moved. The object can be set into motion only when a force, such as a push or pull, is applied to it. The force can be furnished only by some form of energy, such as heat, electrical energy, or the energy of the atom. Anything that occupies space is called matter, and all matter has energy. Matter and energy are the two fundamental concepts of physical science. They are different forms of the same thing, and one can be converted into the other. An important scientific principle is that energy cannot be created or destroyed, only changed from one form to another. All matter has mass, and the mass multiplied by its velocity is an object s momentum. A moving car, a running child, or a missile in flight has momentum. Two bodies that have the same mass but different velocities have different momenta, as do two bodies that have the same velocity but different masses. The object with the larger mass or velocity has the greater momentum. Momentum is stated in units such as foot-pounds per second or kilogram-meters per second. The law of the conservation of momentum states that unless an outside force acts on a body, its momentum will stay the same. The law also applies to the total momentum of two or more bodies that collide. The velocity of each of the bodies may be different after the collision, but the total momentum will not be changed. This activity demonstrates the conservation of momentum and energy using two balls of different sizes. DISCUSSION -After the first drop, how high did each ball bounce? -When the balls were dropped together, how high did the small ball bounce? How high did the large ball bounce? PROCEDURE Hold out your hand at shoulder height. Ask your audience to imagine a scale from 0 to 10, with 0 being the ground and 10 being the height of your hand. Pick up the large ball and hold it out at shoulder height. Tell your audience that you are going to drop the ball, and that they should judge (on the imaginary scale) how high it bounces. Pick up the small ball and repeat the demonstration. 31

36 Energy Hold the small ball on top of the large ball at shoulder height and ask the audience what they think will happen to each of the balls if they are dropped. Drop the balls. The small one will shoot off much higher than the sum of the original bounces put together. Repeat the demonstration, asking the audience to closely watch the larger ball. You will see that it hardly bounces at all. Wrap-up: This experiment is all about conservation of energy and momentum. When the balls are dropped together most of the momentum from BOTH balls is transferred to the small ball. Both the kinetic energy and the momentum of any moving object depend on its mass. If the smaller ball receives all the kinetic energy and momentum from the larger ball it will bounce much higher than the original larger ball because it is so much lighter. Add to that the original energy and momentum in the smaller ball and you get a bounce that is much greater than the sum of the two original bounces. There are also complications due to the materials used to make the balls ('bouncy' balls go wild!). This experiment can also be used as a good demonstration of Chaos effects small changes in the initial conditions (e.g. exactly how the two balls are held above one another) can cause large differences in the end result. Note: For indoor spaces, use a small ball that isn't too bouncy or it will go crazy and could potentially do damage. You could try using a long ruler to help the audience judge how high the balls bounce (some audiences have difficulty with that part and don't get so involved). 32

37 Energy Comeback Can Passport Question: energy is stored energy. energy is energy in motion. Background information Energy comes in many forms. One form of energy is motion, called kinetic energy. Another form is stored energy, or potential energy. Potential energy is the energy that a body has because of its position, composition, or state. For example, potential energy is contained by a raised ball (by virtue of its position), a stick of dynamite ( by virtue of its composition), and a compressed spring (by virtue of its state). Kinetic energy is the energy a body has because of its motion or activity. When a raised ball is dropped, its potential energy changes into kinetic energy as it falls; as it bounces up from the ground, some of its kinetic energy changes back into potential energy. The law of conservationn of energyy states that t energy cannot be created or destroyed. It can change to different forms but it is always the same amount of energy. So, the total amount of kinetic and potential energy is always thee same. SETUP Punch two holes in the lid and the bottom of the can.. Cut the rubber band once so it is one long strip. Thread the rubber band through the holes in the bottom of the can so that both ends are inside the can. Stretch the ends of the rubber band through the holes on the lid of the can. Secure the lid in place and tie the ends of the rubber band together. 33

38 Energy Wrap the pipe cleaner (or twist tie) around the hex nut. You should have two "bunny ears" of equal length sticking up when you're done. As you hold the lid away from the can (a partner can help), wrap each "bunny ear" around one of the rubber bands that runs through the inside of the can. The hex nut should hang from the middle of the rubber bands. DISCUSSION PROCEDURE Ask thee students what they know about kinetic -Talk about kinetic and potential energy. What and potential energy. Accept any answers. are some examples of each? Show them the two cans. Roll the normal one and ask for their observations. Now roll the - How does the can store potential energy and secondd one. What happened? If you time it just change it to kinetic energy? right, you can figure out when the can will start to roll back to you.. Then you can "tell" the can -What do kinetic and potential energy have to to come back, so that it looks like the can is do with a roller coaster? doing what you tell it to do! Open the can and show the students the inside. Wrap-up: To understand how the Comeback Can works, you have to understand energy. When you push the can, you give it kinetic energy and it moves away from you. The hex nut holds one length of rubber band still while the rollingg can causes the other rubber band to twist around it. The can rolls until the rubber band is completely twisted. This is when kinetic energy becomes potential energy - the can is not moving, but it has the ability to do so. As the rubber band unwinds, the potential energy again becomes kinetic energy and the can rolls back to you. The same principle applies to roller coasters. When the train is at the top of the hill it has high potential energy. When it goes down the hill the potential energy becomes kinetic energy and the train picks up speed. Passport Answer: Potential energy is stored energy. Kinetic energy is energy in motion. 34

39 Energy Burning Calories Passport Question: What unit measures the energy inn our food? Background: Plants create their own energy through photosynthesis, but humans and animals cannot. Where do we get energy? From the food we eat! The amount off energy stored in food is measured in calories. One calorie is the amount of energy it takes to raise the temperature of one milliliter of water one degree Celsius. We tend to associate calories with food, but they apply to anything containing energy. For example, a gallon (about 4 liters) of gasoline contains about 31,000,,000 calories. The calories shown on most food labels are written with a capital C and represent one kilocalorie or 1,000 calories. Carbohydrates and fats aree two main sources of energy in foods. SETUP Each group will need a holder for the food they are investigating. Bend a paper clip so that it looks like the image on the student sheet and anchor the base with clay. 35

40 Energy DISCUSSION -Do all kinds of food produce the same amount of energy? - What are some other examples of foods with carbohydrates and fats? Have you eaten any today? PROCEDURE Ask students to predict which provides more energy-the same portion of a carbohydrate-rich food (cereal) or an oil-rich food (pecan). Have students follow the instructions on their sheet. They will pour 50mL of water into the soft drink can and measure the temperature of the water. Next they will hang two oat cereal pieces on the paper clip and light them from below. They should hold the beaker with the bottom about one inch above the flame. If necessary, they should relight the cereal pieces until they will no longer burn. They should record the final water temperature. Have students repeat the process with the pecan (place on top of holder). Have students calculate the number of calories released by each food. What are the results? Wrap-up The food we eat can have very different amounts of calories. Carbohydrates are found in foods such as cereal, bread, pasta, vegetables and fruits and provide four Calories per gram. Fats are in nuts, meat, butter and milk and provide about nine Calories per gram. Most people get about half of their energy from carbohydrates. Fats provide more energy per gram but are not as healthy. But how do we get the energy contained in the cereal or the nut? Food must be digested before the body can use the energy. Digestion changes food into substances like glucose, a simple sugar, which can be carried in the bloodstream to provide energy for cells throughout the body. Passport Answer: Calories 36

41 Energy Some Like It Hot Passport Question: Name one type of heat transfer and an example. Background: The threee methods of heat transfer are conduction, convection and radiation. Conduction is the transfer of heat between objects that are in physical contact. Convection is the transfer of energy between an object and its environment due to fluid motion. Radiation is the transfer of heat as waves of energy that can travel through space. Boiling a pot of water is a good example of these. The pot is touching the stove, and the heat from the stove transfers to the pot throughh conduction. If you touch the pot, heat is conducted to your hand. As the water at the bottom of the pot gets hot it rises to the top, and the colder water moves to the bottom of the pot where it is heated too. You can feel the heat from the stove without touching it the heat moves through the air by radiation. DISCUSSION - What does the word hot mean? What are some substances thatt you know are hot? - Conduction is the transfer of heat between objects that are in physical contact. Example: touching a hot stove. - Convection is the transfer of energy between an object and its environment due to fluid motion. Example: a hot air balloon. PROCEDURE Tell thee students they will investigate heat at three different stations. This heat comes from a source and interacts with other matter. It will be their challenge to discover the source of the heat, how it gets to the material, and how it interacts with it. Stationn 1: Show students the setup and ask how they can melt the wax dots in order without puttingg heat directly on the wax. This can be done by heating the rod with the burner. What is the heat source? 37

42 Energy - Radiation is the transfer of heat as waves of energy that can travel through space. That is how the Earth gets heat from the Sun. Station 2: Ask the students to get the paper to twirl, without touching it, with only the given equipment. This is done by holding the paper spiral over the light bulb. What is the heat source? Station 3: Position the prism so that the light spectrum can be seen on a tabletop. Place one thermometer on each end of the spectrum (infrared and ultraviolet). Place the third on any color the students choose. Allow the thermometers to get a reading-accurate measurement is critical! Compare the temperature readings. Are there any differences? What is the heat source? Wrap-up: What is going on? In Station 1, the metal rod is touching the wax dots, and when it is heated the rod conducts the heat to the wax. In Station 2, the light bulb heats the air around it, and hot air rises. The rising air acts as a current that moves through the paper spiral and causes it to spin. In Station 3, light from the sun is split in the prism. All of the wavelengths carry energy, and we experience them in different ways. We can see the visible light wavelengths. We can t see infrared or ultraviolet light, but we can feel the infrared light as heat. Heat vision technology is really detecting infrared light! Passport Answer: Conduction, convection or radiation. Examples will vary. 38

43 Energy Van de Graaff Generator Passport Question: Name the three parts of an atom. Background: To understand the Van de Graaff generator and how it works, you need to understand static electricity. Almost all of us are familiar with static electricity because we can see and feel it in the winter. On dry winter days, static electricity can build up in our bodies and cause a spark to jump from our bodies to pieces of metal or other people's bodies. We can see, feel and hear the sound of the spark when it jumps. In science class you may have also done some experiments with static electricity. For example, if you rub a glass rod with a silk cloth or if you rub a piece of amber with wool, the glass and amber will develop a static charge that can attract small bits of paper or plastic. To understand what is happening when your body or a glass rod develops a static charge, you need to think about the atoms that make up everything we can see. All matter is made up of atoms, which are themselves made up of charged particles. Atoms have a nucleus consisting of neutrons and protons. They also have a surrounding "shell" that is made up of electrons. Typically, matter is neutrally charged, meaning that the number of electrons and protons are the same. If an atom has more electrons than protons, it is negatively charged. If it has more protons than electrons, it is positively charged. When two non-conducting materials come into contact with each other, one material may "capture" some of the electrons from the other material. If the two materials are now separated from each other, a charge imbalance will occur. The material that captured the electron is now negatively charged and the material that lost an electron is now positively charged. This charge imbalance is where "static electricity" comes from. The term "static" in this case is deceptive, because it implies "no motion," when in reality it is very common and necessary for charge imbalances to flow. The spark you feel when you touch a door knob is an example of such flow. Now that you understand something about electrostatics and static electricity, it is easy to understand the purpose of the Van de Graaff generator. A Van de Graaff generator is a device designed to create static electricity and make it available for experimentation. DISCUSSION -Why does your hair stand on end when you touch the Van de Graaff generator? -How does the light bulb light up? PROCEDURE Crank the Van de Graaff generator by hand to produce static electricity. While cranking the generator place the big wand within proximity of the large ball at the 39

44 Energy -How does the aluminum can roll without you touching it? top of the generator and notice the arc current between the 2 balls. Have the student stand on the plastic stool and place one hand on the generator, keeping the other hand free. Crank the generator for 1-3 minutes. Rub the balloon against their hair to speed up the process. Experiment with the light bulb and the aluminum can. Can you make the bulb light up by charging/heating the gasses inside the bulb with energy? Lay the aluminumm can on the table. Can you make it roll without touching it? Wrap-up: The Van de Graaff generator is an electrostatic generatorr which usess a moving belt to accumulate very highh electrostatically stable voltages. Look at how thee silk belt rubs against the felt wheel at the bottom of the generator -- as the silk and felt come in contact with each other they produce electrons (negatively charged particles) that are captured by the ball; ; this is also known as static electricity. The small wand is capturing protons (positivelyy charged particles.) Why does your hair stand on end? Because the generator is charging you with electrons and each of the strands of your hair have the same net charge -- like charges repel each other, so each of your hair strands want to move away from each other. Passport Answer: Proton, neutron and electron. 40

45 Energy Static Soybeans Passport Question: Like charges and opposite charges. Background: Have you ever gotten a shock from touching a doorknob?? Or gone down a plastic slide and had your hair stand on end? Then you ve experienced static electricity. All matter is made up of atoms, which are themselves made up of charged particles. Atoms have a nucleus consisting of neutrons and protons. They also have a surrounding "shell" that is made up of electrons. Typically, matter is neutrally charged, meaning that the number of electrons and protons are the same. If an atom has more electrons than protons, it is negatively charged. If it has more protons than electrons, it is positively charged. Positive and negative are attracted to each other, but two negative or two positive charges together will repel each other. Static electricity is an excess of electric charge on the surface of an object. The charge iss released by escaping to an object with the opposite charge. We often see and feel this as a shock. In the diagram, a balloon with a negative charge attractss the positive charges in the neutral piece of paper. This activity creates attraction and repulsion by y giving charges to soybeans and plastic spoons. DISCUSSION - How do the beans move? How do they settle? Do they come close together or push each other apart? - Once the beans have stopped moving, try passing your hand close under the beans but not touching the balloon. What happens? PROCEDURE For thee first activity, place threee soybeans into the balloon. Blow up the balloon, but not all the way, and tie it. Rub thee balloon, with the beans inside, back and forth against your pants leg or your hair for about 20 seconds. After the allotted time, stop moving the balloon and let the soybeans settle. 41

46 Energy - We know that like charges repel and opposite charges attract. Which type of charges build up on the beans based on your observations? - Why is the pepper attracted to the spoon? Why isn t the salt? For the second activity, mix salt and pepper in a bowl. Ask the students to separate the two using only the plastic spoons. Challenge them to think creatively! Students may figure out that they can use static electricity to complete the task. If not, drop a hint. Rubbing the spoon on their hair, wool, or polyester fabrics will statically charge it and they ll be able to pick up the pepper. Wrap-up: In the first activity, rubbing the balloon generates static electricity. Friction can separate positive and negative charges. As positive and negative charges build up on the beans, beans with like charges repel each other and beans with positive charges attract. In the second activity, the spoon gains a negative charge when it is rubbed on hair or fabric. It can then attract positively charged particles or the positive charges on neutral substances (such as flecks of pepper). The statically charged spoon does not affect the salt because salt has an extremely stable molecular structure held together with strong ionic bonds. The bonds are too strong for the negative charge on the spoon to have any effect, so only the pepper is attracted to the spoon. Passport Answer: Like charges repel and opposite charges attract. 42

47 Energy Human Battery Passport Question: What is the name of an object that allows electrons to flow through it? Background: To understand electricity, we must first understand the makeup of atoms. Each atom consists of positively-charged protons, negatively-charged electrons, and neutral neutrons. An electrical current occurs when the negative electrons flow through a conductor. A conductor is any object that allows the electrons to flow through it common examples are copper, iron and salt water. Many metals can conduct electricity, but they are not all equal. When two metals are connected in a circuit by electrically conducting materials, such as a wire, electrons will flow along the wire between them. This experiment will test which combination of metals produces the most electrical current using the human body as the conductor. SETUP Using the cloth tape, attach the micro-ammeter in the center of the board. Cut four lengths of wire each about 18 in. long. Punch a hole near one end of each metal sheet and attach one end of an 18-in. piece of wire to the metal sheet by threading it through the hole. Attach the metal sheets to the wooden board by taping the sides onto the board. Place AI (aluminum) and Zn (zinc) on the left of the micro-ammeter, and Cu (copper) and Fe (iron) on the right. The metal sheets should not touch each other. Connect the wires from the Al (aluminum) and Zn (zinc) to the negative terminal of the meter. Connect the wires from the Cu (copper) and Fe (iron) to the positive terminal of the meter. Label the appropriate metal sheets AI (Aluminum), Zn (Zinc), Cu (Copper), and Fe (Iron). DISCUSSION -An electrical current is produced when electrons flow through a conductor. In this case you are the conductor! - Current is measured in amperes (A), often shortened to amps -People with sweaty hands often produce more current. Why is that? Sweat is salty and salt is a good conductor of electricity. - A battery works because it has a positive and negative end. A salt solution acts as conductor the electrons flow from the negative PROCEDURE Ask the students what they know about batteries. Tell them that today they will be a battery! Show them the setup and explain that the micro-ammeter measures electric current in micro-amperes. Instruct them to place their left hand on the aluminum or zinc panel and the right hand on the copper or iron panel. What happens to the needle on the meter? Tell them to try different combinations of metals to see which makes the needle move the most, keeping on hand on either side of the microammeter. Which combination has the best result? 43

48 Energy end to the positive end and an electric current is created. Wrap-up When you touch the two metal plates, the thin film of sweat on your hands acts like the acid in a battery, reacting with the negative plate and with the positive plate. For example, your hand takes negatively charged electrons away from the copper plate, leaving positive charges behind. At the same time, your hand gives electrons to the aluminum plate, causing it to become negatively charged. This difference in charge between the two plates creates a flow of electrical charge, or electrical current. Since electrons can move freely through metals, the excess electrons on the aluminum plate flow through the meter on their way to the copper plate. (In metals, positive charges cannot move.) In your body, both positive and negative ions move. Negative electrons move through your body from the hand touching the copper to the hand touching aluminum. At the same time, positive ions move in the opposite direction. As long as the reactions continue, the charges will continue to flow and the meter will show a small current. Your body resists the flow of current. Most of this resistance is in your skin. By wetting your skin you can decrease your resistance and increase the current through the meter. Different people will get different results as to which combination works the best. Cu (copper) and AI (aluminum) should produce the most current. This is basically how batteries work. In a battery, the metals are connected by some sort of salt bridge a typical alkaline battery uses potassium hydroxide. A salt bridge allows the passage of a charge to complete the electrical circuit but does not allow the flow of the electrons. The electrons are then forced to travel through the wire, thus creating a current. In this display, the visitor becomes the salt bridge. More current will be produced when hands are very sweaty. Passport Answer: A conductor 44

49 Energy Currently Working Passport Question: A solution must have to be able to conduct electricity. Background: The most common conductors of electricity are metals andd solutions. A solution is a mixture in which two substancess are mixed uniformly an example is salt water. When an acid, a base, or a salt is dissolved in water, the molecules break into electrically charged particles called ions. A solution can conduct electricity if it contains ions. In this experiment students will determine which solutions are able to conduct electricity using an LED bulb. SETUP Attach the LED bulb to the battery and position the copper wire so it is attached to the battery and has two terminal ends that are close to each other but not touching. Prepare the solutions- one is plain tap water, the other is saline. DISCUSSION -Make a prediction as to whether or not solution one or two, or both or neither, will light up the bulb. -What is needed to carry an electric current? (Charged particles or ions) - Which solutions caused the bulbb to light up? Why did those work? (They have ions!) PROCEDURE Ask thee students if they have ever been in a thunderstorm at the beach or the pool. Could they stay in the water? Why or why not? Tell them that this experiment has to do with conducting electricity in solutions. The students will be testing which solutions conduct electricity and lightt up the bulb. Make sure they are wearing safety goggles! Demonstrate the light by touching the ends of 45

50 Energy -Was there any other reaction that you observed, other than the bulp lighting up? (look for bubbles in the water) the copper wires to the copper strip. The bulb should light up. Each one of the cups should have 10mL of one of the four solutions. Have the students place the ends of the copper wires into each solution WTIHOUT the ends touching. Do not let the 2 wire ends touch! Be sure to rinse the wires between each solution. Wrap-up: When the two terminals touch the piece of metal, the current is carried entirely by electrons that can move through the wire and metal. But if the two terminals are connected by a solution, the current is carried only if there are charged particles in the solution to carry it. Solutions like the salt water have ions and so are able to conduct electricity. The bubbles you see are caused by electrons separating from the salt molecules. Because pure water has few ions, it is a poor conductor. Uncharged molecules that dissolve in water, like sugar, do not conduct electricity. If there are ions, positive ions will move in one direction, negative ions will move in the opposite direction, and the electric current can move and light up the bulb. The salt water of the ocean and the chlorine water in the pool are both solutions with ions, so it is dangerous to swim during a thunderstorm you might be on the receiving end of the electric current! Passport Answer: A solution must have ions to be able to conduct electricity. 46

51 Energy Homemade Motor Passport Question: What is the interaction of electric and magnetic fields called? Background: You are about to construct a simple motor based on the principles of electromagnetism. Electromagnetism is the branch of science concerned with the forces that occur between electrically charged particles. When these charged particles move they create an electromagnetic field, an invisible field that can travel through solid objects and extend far away from their sources. We can see that the word itself refers to electricity and magnetism this is because the two concepts are related. A changing electric field generates a magnetic field, and a changing magnetic field generates an electric field. This simple homopolar motor shows how moving charges (an electric current) experience a force when they move through a magnetic field. DISCUSSION - Why does the magnet only spin when the copper wire touches it? -How does the magnet keep spinning even though the copper wire isn t touching it? PROCEDURE Use the watch battery to power one of the LED lights. To do this, slide the watch battery between the wires of the LED light. Press one of the LED wires against the positive side of the battery and the other wire against the negative side of the battery. Tape down the LED wire that is touching the negative side of the battery. Slide one wire from the other LED light underneath the piece of tape. The LED light's second wire should be against the positive side of the battery. Carefully place the neodymium magnet against the positive end of the watch battery. At this point, both LED lights should be lit up. Place the head of the screw in the center of the magnet opposite the LED lights. Place the tip of the screw in the center of the negative end of the C battery. Use the copper wire to touch the positive end of the C battery and the neodymium magnet and the motor will begin spinning. 47

52 Energy Wrap-up: What you have created is called an electromagnetic or homopolar motor. This motor is called homopolar because there is no change of polarity in the wire. An electromagnetic motor works through a magnetic field along the axis of rotation and an electric current that, at some point, is not parallel to the magnetic field. How does that work? You have an electric current flowing throughout the circuit. The current, at some point while traveling through the system, is not parallel to the magnetic field of the neodymium magnet. At the point where the forces of the current and magnetic field are not parallel, there is a force called a Lorentz force. The Lorentz force occurs in electromagnetic fields, such as the one we've created with this system. The direction of the force is perpendicula r to both the direction of the current and the direction of the magnetic field, as demonstrated by the Left Hand Rule below. It is the Lorentz force that causes the screw to rotate. When you connect the positive end of the battery to the neodymium magnet (attached to the negative end of the battery by way of the screw) you create the necessary electromagne etic field to produce the Lorentz force. But since there is such a small amount of friction between the screw and battery, the Lorentz force directly affects the magnet. The magnet and screw continue to spin long after you've removed the wire that closes the system because of the small amount of friction. Passport Answer: Electromagnetism 48

53 Energy Conductor or Insulator? Passport Question: An object that allows electricity too flow is a. An object that prevents electricity from flowing is a. Background: When you load a battery into an electronic device, you're not simply unleashing the electricity and sending it to do a task. Negatively charged electronss want to travel to the positive portion of the battery -- and if they have to rev up your personal electric shaver along the way to get there, they'll do it. The source of electricity must have two terminals: a positive terminal and a negative terminal. The electrons must flow from the negative terminal to the positive terminal through a copper wire or some other conductor. The moving electrons transmit electrical energy from one point to another. When there is a path that goes from the negative to the positive terminal, you have a circuit, and electrons can flow through the wire. You can attach any type of receiver, such as a light bulb or motor, in the middle of the circuit. The source of electricity will power the receiver, and the receiver will perform whatever task it's designed to carry out, from spinning a shaft to generating light. The diagram below shows a simple circuit, with the path of the electrons following the red arrows. Most circuits can be turned on and off with a device called a switch. A switch completes the circuit and allows electricity to flow. When an object allows electricity to flow through it, we call that a conductor. When an object prevents electricity from flowing through it, it is an insulator. DISCUSSION -Once the motor is running, can you trace the flow of electricity? PROCEDURE Challenge the students to make the motor run on the circuit board. Once they have completed the circuit, show them the tray of items. Tell them to predict and 49

54 Energy -Why does the motor only run when the switch is on? What is the purpose of the switch? then test which ones are insulators and which are conductors. -Were your prediction about the insulators and conductors correct? Why do you think some materials conduct and others don t? Wrap-Up: In the first activity, the motor can only run when the switch is closed and the circuit is complete. Electricity needs a complete pathway from the source, to the receiver, and back to the source in order to run the motor. When the switch is open, there is no flow of electricity so the motor doesn t run. But when the switch is closed, electricity can flow through the circuit, and the motor runs. In the second activity, students will probably note that metals conduct electricity and non-metals do not. This is because in many materials, the electrons are tightly bound to the atoms. Wood, glass, plastic, ceramic, air, cotton -- these are all examples of materials in which electrons stick with their atoms. Because these atoms are so reluctant to share electrons, these materials can't conduct electricity very well, if at all. These materials are electrical insulators. Most metals, however, have electrons that can detach from their atoms and zip around. These are called free electrons. The loose electrons make it easy for electricity to flow through these materials, so they're known as electrical conductors. Passport Answer: An object that allows electricity to flow is a conductor. An object that prevents electricity from flowing is an insulator. 50

55 Energy Bubble Trouble Passport Question: What is the name of the process that creates a rainbow? Background: Light travels in waves each type of light has its own wavelength and frequency. There are many types of light we cannot see, including microwaves, ultraviolet and X-rays. The light that we can see is called the visible spectrum, or white light. The light from the Sun or a light bulb looks white or yellow, but it s actually made of many different colors. You have probably seen this spectrum in a rainbow: red, orange, yellow, green, blue, indigo and violet. How can white light contain so many colors? You re about to find out using bubbles! DISCUSSION -Do you see rainbows when you look out through the bubble? - What causes the rainbows you see? How does a rainbow in the sky form? PROCEDURE Make sure everyone has their safety goggles on! Have the participant stand on the stool in the center of the kiddie pool (their hands must be at their sides!) Facilitators must first cover their own hands with the bubble solution, then grab the hula-hoop and SLOWLY raise it over the participant s head. Tell them to observe the light as it travels through the bubble. What do they see? Wrap-up: The fundamental process at work in a rainbow is refraction -- the "bending" of light. Light bends -- or more accurately, changes directions -- when it travels from one medium to another. This happens because light travels at different speeds in different mediums, such as air and water. Additionally, different colors of light have different frequencies, which cause them to travel at different speeds when they move through matter. You may have seen this effect with a prism. A prism refracts white light into the colors of the rainbow. Water droplets in the air act like a prism. When the white light passes from air into the drop of water, the component colors of light slow down to different speeds depending on their frequency. Each color of light bends at a different angle as it passes through the drop of water. In this way, each individual raindrop disperses white sunlight into its component colors. 51

56 Energy So why do we see wide bands of color, as if different rainy areas were dispersing a different single color? Becausee we only see one color from each raindrop. You can see how this works in the diagram below: When raindrop A disperses light, only the red light travels at the correct angle to enter the observer' 's eyes. The other colored beams exit at a higherr angle, so the observer doesn't see them. The sunlight will hit all the surrounding raindrops inn the same way, so they will all bounce red light onto the observer. Raindrop B is much lower in the sky, so it doesn't bouncee red light to the observer. At its height, the violet light exits at the correct angle to travel to the observer's eye. All the drops surrounding raindrop B bounce light in the same way. The raindrops in between A and B all bounce different colors of light to the observer, so the observer sees the full color spectrum. If you were up above the rain, you would see the rainbow as a full circle, because the lightt would bounce back from all around you. On the ground, we see the arc of the rainbow that is visible above the horizon. In this activity, the bubble acts like the raindrops. Light is bent at different angles as it passes through the bubble. We see different colors in the bubblee depending on the angle of the light that reaches our eyes. Passport Answer: Refraction 52

57 Energy Color Combinations Passport Question: Name the primary colors of light. Background: We all know the colors of the rainbow- red, orange, yellow, green, blue, indigo and violet (Roy G. Biv). But where do colors like pink and brown come from? We can create many more colors with different combinations of primary colors. The primary colors of light are red, green and blue. When they are combined the color grows lighter and eventually becomes white. What about secondary colors? Secondary colors are colors that can be produced by a mixture of equal parts of two primaries. A mixture of green and blue light, for example, makes cyan; cyan is therefore a secondary color. The colors we see in the rainbow are the primary and secondary colors. In this activity, students experiment with flashlights of the primary colors to create new colors. DISCUSSION -What happens to the intensity of the color when you add more flashlights? -What happens when you have all three colors together? PROCEDURE Put the students in groups of 3 or 4. Give each group a handout and three flashlights with the coloredd gel. Have them use the flashlights to mix different colorss and record them on the sheet. -How many different colors can you make? 53

58 Energy Wrap-up: Now you know about the primary colors! These can be combined even more to form the variety of colors in your crayon box. This is how computer monitors and televisions work using only red, blue and green they make hundreds of different colors that we see on our screens. They do this with pixels small colored dots that our brains assemble into images.. Below are some examples of pixels. Passport Answer: The primary colors of light are red, green and blue. 54

59 Energy Laser Beams Passport Question: True or false: Light can only travel through a medium. Background: We know that light can travel through space because wee can see the light from faraway stars. But there is nothing in space-it is a vacuum. How can light travel through nothing? Light doesn t need a medium to travel through. A mediumm is anythingg made of atoms it can be solid, liquid, or gas. Even humans can be mediums! Light travels in a straight line until it encounters matter; then it is reflected, refracted or absorbed. What we can see is light reflecting off of matter, including tiny particles in the air. This activity tests the properties of light using lasers and fog. DISCUSSION -Outside of the light and dark room, can you actually see the light traveling from the laser to the wall, or do you just see the light at the wall? - Can you see the light traveling from its source to its destination inside of the light and dark room? -Why can you see the light inside the chamber but not outside of it? -What happens to light colored objects under the black light? What happens to dark colored objects? PROCEDURE Outsidee of the light and dark room, turn on a laser and point it at the wall. What do you see? Enter the light and dark room with the laser and point it at the wall again. What do you see? Shine the laser at a mirror. Observe the effect. Try to reflect the laser beam offf of as many mirrorss as possible. Notice if the glow from the black light is reflecting off of anything. Get close to the black light and look at your eyes and teeth in the mirror. 55

60 Energy Wrap-up: The laser is doing the same thing inside and outside of the light and dark room. Outside of it there are not enough particles in the air to reflect the light so we can only see it on the wall. Inside the light and dark room, the particles in the fog reflect the light and we can see the light from the laser traveling through the room. The beam exists in both cases, but we can only see it when there are enough particles in the air to show it to us. Under the black light, light-colored objects such as teeth reflect light that is why they appear to glow. Dark-colored objects absorb light and are more difficult to see. Passport Question: False light does not need a medium to travel through. 56

61 Energy Light Fountain Passport Question: What is the main principle that lets fiber optics work? Background: You hear about fiber-optic cables whenever people talk about the telephone system, the cable TV system or the Internet. But what is fiber optics? Fiber optics is the technique of transmitting light through transparent, flexible fibers of glass or plastic. The fibers, called optical fibers, can channel light over a curvedd path. Bundles of parallel fibers can be used to illuminate and observe hard-to-reach places. Optical fibers of very pure glass are able to carry light over long distancess ranging from a few inches or centimeters to more than 100 miles (160 km) with little dimming. Cables containing such fibers are used in certain types of communicat tions systems. Some individual fibers are thinner than human hair and measure less than inch (0.004 mm) in diameter! But how do these fibers transmit light? Suppose you want to shine a flashlight beam down a long, straight hallway. Just point the beam straightt down the hallway -- light travels in straight lines, so it is no problem. What if the hallway has a bend in it? You could place a mirror at the bend to reflect the light beam around the corner. What if the hallway is very winding with multiple bends? You might line thee walls with mirrors and angle the beam so that it bounces from side-to-side all along the hallway. This is exactly what happens in an optical fiber. The light in a fiber-optic cable travels through the core (hallway) by constantly bouncing from the cladding (mirror-lined walls), a principle called total internal reflection. Because the cladding does not absorb any light from the core, the light wave can travel great distances. With the simplest form of optical fiber, light entering one end of the fiber strikes the boundary of the fiber and is reflected inward. The light travels through the fiber in a succession of zigzag reflections until it exits from the other end of the fiber. 57

62 Energy In this activity students will create a simple optical fiber using a light source and water. SETUP Place a 2-inch piece of duct tape on the side of the bottle to create a patch. Use the corkscrew to punch a hole in the center of the tape patch. Stick a piece of painters tape over the hole in the bottle. (Later, you will be able to pull off the blue tape without pulling off the duct tape). DISCUSSION -How does the light enter the bottle and what does it do as it comes out of the hole? -What happens if you catch the water in another container like a bowl as it drains? PROCEDURE Fill the bottle with water. Turn on the flashlight and turn out the lights. With one hand, hold the bottle over the bucket or the edge of the sink. With your other hand, hold the flashlight on the side of the bottle across from the hole. Remove the blue tape. Have students observe what happens. Wrap-up: The light ray inside the stream of water behaves as it would inside an optical fiber. A light beam sent into one end of the fiber comes out the other end, just as light travels through the stream of water in your experiment. It doesn t matter if the fiber is straight, curved, or bent into loops; the light beam travels all the way through and comes out the other end. The light beam bounces around inside the fiber, reflecting back and forth off the walls. It doesn t pass through the walls and out of the fiber, and it doesn t stop until it comes out the far end. This is total internal reflection. Passport Answer: Total internal reflection 58

63 Energy Why is the Sky Purple? Passport Question: What process gives the sky its color? Background: Wait, the sky isn t purple it s blue! So why are we asking about purple? The short answer is scattering. In this activity we ll find out what this is and how it affects the color of the sky, and we ll also see why the sky is purple! The first person to correctly work out the details of the process that gives rise to the color of the sky was the English physicist Lord John Rayleigh, workingg in the late 1800 s. The atmospheree doesn t absorb light, but the molecules in the atmospheree do redirect it. As the light passes through the atmosphere, the atoms actually absorb and reemit the light. This doesn t change the intensity of the light, but it does change the direction. Andd this change in direction which we call scattering is ten times stronger for violet light than forr red. This particular type of scattering is called selective scattering or Rayleigh scattering. Blue light has a short wavelength and a high frequency, so it is strongly scattered. When you lookk up at the sky, any light that you seee has been redirected toward your eyes it has been scattered. Because you are seeing only scattered light, the sky appears blue. But violet light has an even shorter wavelength and a higher frequency than blue light, so by all accounts the sky light should be violet! It appears there is more to the story! If we judge by the most prominent color, the sky is violet.. But the sky appears blue due to the limitations of our eyes. Our sensitivity to light decreases ass we reach the shortest wavelengths of the visible spectrum. The violet is there, but our eyes detect it only weakly. What we see is blue present in large quantities and easily detected by our eyes. DISCUSSION -What color is the scattered light? PROCEDURE Place a white light at one end of the sunset egg. Look at the light that comes out of the side of the egg. This is the scattered light. 59

64 Energy -What color is the transmitted light? -How would you use this experiment to explain blue skiess and red sunsets? Next, look at the light that goes through the egg. This is the transmitted light- all of the light that isn t scattered. Try the light on the other end of the egg, or on the egg s side. What do you notice now? Wrap-up: The scattering from the crystals in the egg is selective scattering just like in the atmosphere. Blue light is scattered out of the egg and is seen from the side.. The longer wavelengths, red and orange, can pass through the eggg without being scattered. At sunrise and sunset we see the sun at an angle, and the light has to pass through12 times more of the atmosphere to get to our eyes. All of the shorter wavelengths scatter away and we are left with the beautiful reds and oranges of the sunrise and sunset. Passport Answer: Scattering or Rayleigh scattering 60

65 Energy Flying Mirror Passport Question: Where is the image that we see inn a mirror? Background: Optical illusions occur when what we see does not match what is actually happening. The brain can be tricked into seeing something that isn t reallyy there, or that isn t what it appears. This activity uses the properties of mirrors and reflection to create the illusion that a person can fly. DISCUSSION -Tell the students observing to watch carefully. Is the student really flying? Why do we think he or she is? PROCEDURE Mount the mirror vertically. Instruct the student to standd with one foot in front of the mirror and one in back. Mark a spot on the floor for them to standd on. Tell them to balance on the foot that is behind the mirror and lift the one that is in front of it. To the observers, both legs appear to leavee the ground! Wrap-up: Most people have noticed that images in a mirror do not look exactly the same as the object. There are two properties of reflected images that accountt for this particular illusion. The first is the position of the image. The image is not on the mirror but is actually formed behind the mirror. It is as far behind the mirror as the object is in front, as shown in the image below. Thus, the reflected image of the lifted leg appears at about the same position behind the mirror as the demonstrator's "second" leg. So our brain tries to tell us that the image is the leg behind the mirror. 61

66 Energy The second property that also helps fool our brain is the orientation of the image. Nearly everyone has observed that if a person parts their hair on the right, their image in a mirror has hair parted on the left side. Most people, therefore, say that mirrors switch images from side to side but this is WRONG! When someone holds an arrow vertically upright in front of a mirror, the image is also vertically upright. If the arrow is held horizontally pointing towards one side of the mirror, the image also points to the same side of the mirror. We can therefore conclude that the vertical and horizontal orientations of reflected images are unchanged. But a mirror does change something. When the arrow is pointed directly into the mirror, the image of the arrow points outward in the opposite direction. Or, when we look into a mirror our image looks back at us. Thus, a mirror only changes the direction the object is facing into and out of the mirror. When we apply the above to our leg and a mirror, we find that the leg and its image are both upright because the mirror has not inverted the image. We also observe that the foot is pointing in the same way because the mirror has not reversed things from side to side. However, since a mirror does change the direction the image faces, the inside of the leg which would normally face away is now reflected back towards an observer. When we look at a person's legs we see the outside of one leg and the inside of the other. So, when we observe a person's leg in front of a mirror and the reflection from the inside of the same leg, we naturally assume that the image is actually the person's other leg. Since the image is in the same position and orientation as a leg on the other side of the mirror, our brain is convinced that it is making a normal observation. When the leg in front of the mirror is lifted, the image is lifted and our brain is fooled into telling us that the person has lifted both of their legs and has actually floated off the ground. Passport Answer: Behind the mirror specifically, as far behind the mirror as the object is in front of it. 62

67 Energy Super Spectroscopes Passport Question: What is the name of the tool that uses light to identify elements in faraway stars? Background: A spectroscope is a device that can be used to look at the group of wavelengths of light given off by an element. All elements give off a limited number of wavelengths when they are heated and changed into gas. Each element always gives off thee same group of wavelengths. This group is called the emission spectrum of the element. In the visible wavelengths of the electromagnetic spectrum, red, with the longest wavelength, is diffracted most; and violet, with the shortest wavelength, is diffracted least. Because each color is diffracted a different amount, each color bends at a different angle. The result is a separationn of white light into the seven major colors of the rainbow, or spectrum. This happens due to a process called diffraction. Diffraction is the spreading out of waves, such as those of water, sound, or in this case light, as they pass around an obstacle or go through an opening. When light strikes a diffraction grating, a small sheet off glass marked with thousands of parallel lines, diffraction causes the light waves to spread in such a way that they produce a spectrum, or rainbow. The diagram below compares the refraction, reflection and diffraction of light. DISCUSSION - When you look through the spectroscope, you can see bands of color. What colors do you see? Do they fade or blend into each other? PROCEDURE First, have the students observee each of the light sourcess with the naked eye. What do they see? Now look at the light sources through the spectroscopes provided. Tell them to write down the colors they see. 63

68 Energy -Does each light source produce the same group of colors or spectrum? -Why are the groups of color for each light source different? The students can make their own spectroscope to take home. Tell them to observe different light sources, including lights at night. Be sure not to look directly into the Sun! Wrap-up: Simple spectroscopes, like the one described here, are easy to make and offer users a quick look at the color components of visible light. Different light sources may look the same to the naked eye but will appear differently in the spectroscope. The colors are arranged in the same order but some may be missing and their intensity will vary. The appearance of the spectrum displayed is distinctive and can tell the observer what the light source is. One of the important applications of spectroscopes is their use for identifying chemical elements. Each element radiates light in specific wavelength combinations that are as distinctive as fingerprints. Knowing the spectral signatures of each element enables astronomers to identify the elements present in distant stars by analyzing their spectra. They also allow astronomers to analyze starlight by providing a measure of the relative amounts of red and blue light a star gives out. Knowing this, astronomers can determine the star s temperature. They also can deduce its chemical composition, estimate its size, and even measure its motion away from or toward Earth. Passport Answer: A spectroscope. Identify mystery krypton? 64

69 Energy Catch the Wave! Passport Question: What kind of wave is a sound wave? Background: Just like light, sound travels in waves. A vibrating object creates the waves. For example, when you play a drum, the drumhead starts vibrating. As the drumhead vibrates, it bumps into air molecules and starts them bouncing to and fro. The air molecules that strike the drumhead while it is movingg outward bounce back from it with more than their normal energy and speed, as if the drumhead pushed them. These faster- moving molecules move into the surrounding air. Forr a moment, the region next to the drumhead has a greater than normal concentration of air molecules it becomes a region of compression. As the faster-moving molecules overtake the air molecules in the surrounding air, they collide with them and pass on their extra energy. The region of compression moves outward as the energy from the vibrating drumhead is transferred to groups of molecules farther and farther away. Air molecules that strike the drumhead while it is moving inward bounce back from it with less than their normal energy and speed. For a moment, then, the region next to the drumhead has fewer air molecules than normal it becomes a region of rarefaction. Molecules colliding with these slower-moving molecules also rebound with less speed than normal, and the region of rarefaction travels outward. This chain reaction of moving air molecules carries sound through the air in a series of pulsating pressure waves that we call sound. A sound wave is a longitudinal wave, which means that the vibrations travel in the same direction as the direction of travel.. DISCUSSION -What sound does the empty glass make when tapped? Can you seee the vibration? PROCEDURE Set outt three glasses one with ice, one with water and one empty. Tap each glass and tell students to observee what they see and hear. 65

70 Energy -What about the glass with water? The glass with ice? -What observations can you make about how sound travels through different media? Stretch out the slinky and give one end a push. Have the students observe the wave. Ask them to find the areas of compression and rarefaction. -How does the wave travel along the slinky? What is this kind of wave called? Wrap-up: Sound is a vibration that travels in waves. Sound waves travel through matter it can be a gas, a liquid or a solid. Although we hear most sounds through air, it is not the most efficient way for it to travel. Sound travels about 5 times faster in water and about 14 times faster in steel than in air because the molecules are closer together and the motion can be transferred more rapidly. The next time you go swimming try talking underwater with a friend and see how well you can hear each other! Passport Answer: A sound wave is a longitudinal wave. 66

71 Energy Musical Coat Hangers Passport Question: Which is the best medium for sound: gas, liquid or solid? Background: We know that vibrating objects create sound waves. How do those waves become the sounds we hear? You hear sounds when vibrations get inside your ears and stimulate your nerves to send electrical signals to your brain. When someone plays a drum, sound waves carry vibrations from the drum to your ears. The outer ear or pinna acts as a funnel, bringing the sound waves into the ear. Inside your ear, moving air molecules push on your eardrum and start it vibrating. Your eardrum, in turn, pushes on the bones of your middle ear, the tiniest bones in your body. These bones act like a set of levers, pushing against the thin membrane thatt covers the opening to your inner ear. The movement of this membrane makes pressure waves in the fluid inside the cochlea, where cells with tiny sensing hairs transform thee waves into electrical signals. Thesee electrical signals travel along the auditory nerve to your brain. When these electrical signals reach your brain, you hear a sound the beat of a drum.. In this activity, students learn about how they hear by experimenting with the sounds of different objects. DISCUSSION -What do you hear the first time you bump the coat hanger against something? -What do you hear when you have your fingers in your ear? Is it a different sound? PROCEDURE Tie a 50cm (20 in..) length of cotton thread on each end of a wire coat hanger. Wrap the other end of each thread around your forefingers. Bend over so the coat hanger can swing freely and bump it against a wall or 67

72 Energy -What objects produce the loudest sounds when bumped? -Do you hear anything different with the plastic coat hanger? chair. Try it again, but this time with your forefingers in your ears. Try bumping the coat hanger against different objects. You can also try the activity with a plastic coat hanger. Wrap-up: Why is the sound louder when you have your fingers in your ear? When we hear a sound, it normally travels through air to reach our ears. But sound can also travel through solids and liquids. Solid objects carry sound waves most effectively, then liquids and then gases. In the first part of the experiment, the coat hanger hits a metal object and starts vibrating. The vibrations make sound waves that travel through the air to reach the ears and the sound is very quiet. In the second part, the sound waves travel through the string (a solid material) to reach our ears. Rather than traveling through the air, the vibrations can travel through your hands and through your ear directly to the fluid inside your cochlea in your inner ear. Instead of traveling from solid to air and back to solid, the vibrations move from one solid (the string) to another (your bones), and then into the fluid of your cochlea. As a result, the sound you hear is much louder and richer. The hanger makes the same sound in both situations, but in one you provide a path that lets more of the sound reach your ears. Passport Answer: Solid 68

73 Energy Good Vibrations Passport Question: Where does sound come from? Background: Where does sound come from? The short answer is vibrations. Sound occurs when energy travels as waves of pressure through a substance such as air, water, or even solid materials. Almost anything that vibrates can produce sound. When something vibrates it pushes the particles around it, and those particles in turn push the air particles around them, carrying the pulse of the vibration in all directions from the source. The particles themselves don t move very far, but the transfer of energy can be very fast about 760 miles/hour in air, depending on the temperature and humidity. In this activity students will use different materials to see the vibrations created by tuning forks. SETUP Station 1-Ripples on Water: Add water to the pan or bowl to approximately two inches deep. Place tuning fork next to it. Station 2- Sound Moves: Cut a piece of string approximately one foot long. Tape one end of string to a Ping-Pong ball. DISCUSSION -When we talk, the sound comes from our voice box which is in the throat. You can feel it best if you place your finger lightly on the middle of your throat. -What did you feel when you touched the tuning fork after you hit it? -What happens the first time you touch the Ping- Pong ball with the tuning fork? What happens the second time? PROCEDURE Ask the students, Can you feel the sound of your voice by putting your hand on your body while you talk? Where can you feel it the most? Station 1. Strike a tuning fork against a book and dip the fork in the pan or bowl of water. The students should draw what they see in the water. Station 2. Have one student in a standing position hold the string with the Ping-Pong ball at arm s length. Be sure the student is holding it as still as possible. Have another student gently move the tuning fork towards the Ping-Pong ball until it just barely touches it. Have the student strike the tuning fork again, and this time gently touch the Ping-Pong ball with it. 69

74 Energy Wrap-up: Can we see sound move? In a way, yes! The sound madee by the tuning fork made a pattern of waves that showed in the water. If we could see the air around us, we would be able to see the same kind of waves as sound moves through the air from a radio or a friend to our ears. We also saw that sound can move things. The energy in the tuningg fork is transferred to the Ping-Pong ball. The amount of energy transferred determines how far the Ping-Pong ball moves if you strike the tuning fork harder, the ball will move farther. This sound movement is felt by special parts of your ear (tiny hair cells of the inner ear). Deep inside your ear, sound waves actually move small vibration sensors called hair bundles. Thesee parts of your ear are much smaller than grains of sand. Iff sound is strong (loud) enough, the sound waves cause some of them to bend or break. When you are around loud sounds often, or for a long time, you may begin to have trouble hearing. Passport Answer: Sound is produced by vibrations. 70

75 Energy Better Vibrations Passport Question: What property of sound affects the tone we hear? Background: Sound is created when something vibrates. Vocal cords vibrate to create voices, guitar strings vibrate to create music, doors vibrate when someone knocks on them it all comes down to vibrations. The vibrations are energy and energy can be transferred from one object to another. So in all the above cases, the energy from the vibrations transfers into the air and the air, in turn vibrates until it reaches your ear. Your eardrum then vibrates, causing other structures in your ear to vibrate. All of this, in turn, stimulates nerves that send impulses to your brain which translates it all into how we understand sound. Sounds complicated, and in the details it is beautifully complicated. But, at the heart of it all, sound is vibrations. Let s create a visualizer to help see the vibrations as they travel through the air. SETUP Download the tone generator to your computer or smartphone. Make sure the speaker plays the tone the speaker should already be set up. Cut a hole in the bottom of the cup. Make it just slightly smaller than the speaker. Cut the nozzle of the balloon off. Stretch the round part of the balloon over the top of the cup so it is on tight. Tape or glue the speaker to the bottom of the cup. DISCUSSION -Why does the salt bounce? -What happens when the speaker plays different tones? PROCEDURE Pour salt on top of the balloon. Ask the students what they think will happen when you turn on the speaker. Turn on the speaker. What happens? Try playing different tones. What happens? Note: If the salt doesn t bounce, try turning up the volume. If that doesn t work, change the tone. Wrap-up: As we ve learned, sound is vibrations. But each sound has its own unique vibrations. A tone generator picks one specific tone at a time and creates that specific type of vibration. The vibrations from the speaker pass into the air and then into the balloon, making it vibrate. The vibrations from the balloon make the salt bounce up and down on top of the balloon. Different 71

76 Energy tones create different vibrations which causess the salt to bounce in different patterns. A tone is a sound that repeats at a certain specific frequency. The frequency iss the number of sound waves that pass a given point each second, measured in Hertz (Hz). As we change the frequency of the sound in the speaker, the vibrations of the salt change and we hear a different tone. The higher the frequency, the higher the tone we hear. Some tones won t create patterns. Even though you can hear it, the vibrations don t translate as well into the balloon, so the salt won t dance around like it does at other tones. This could be due to the speaker or the size of the cup. The air and everything is still vibrating, just not in the way needed to make the salt dance. Passport Answer: The frequency 72

77 Forces and Motion Hovercraft Passport Question: What is Newton s 1 st law of motion? Passport Answer: A body at rest stays at rest, and body in motion stays in motion unless other forces act on it. Background Information: Newton s three laws: 1. Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it. 2. The relationship between an object's mass m, its acceleration a, and the applied force F is F = ma. Acceleration and force are vectors (as indicated by their symbols being displayed in slant bold font); in this law the direction of the force vector is the same as the direction of the acceleration vector 3. For every action there is an equal and opposite reaction. Procedure 1 1 st law- Push the person on the hovercraft, explain how a frictionless environment will cause this theory to hold true. 2 2 nd law- Make the person on the hovercraft, heavier/lighter by adding bucket filled with water and show more force is needed to get them moving or the same force will move them slower if more mass is added. 3 3 rd Law- Demo this by throwing a ball back and forth. The person on the hovercraft will be pushed backwards when they throw the ball. Discussion: The hover craft mimics a frictionless environment so Newton s theories can hold true. In an environment with friction the variable of friction must be added. 73

78 Forces and Motion 74

79 Forces and Motion Let s do the Swivel Passport Question: What do physical principle do snowboarders or ice skaters use to spin? Passport Answer: The principle of conserving angular momentum Background information: The law of conservation of angular momentum tells us that you can't just lose momentum - it has to go somewhere. If a thing gets bigger, like a snowball rolling down a hill, then it gains more momentum. If a thing gets smaller (so it has less mass), then it has to spin faster, so that it has the same total momentum. Many athletes use the principle of conserving angular momentum to spin which increases their rate of rotation. Angular momentum is conserved in a system where there is no net external torque, and its conservation helps explain many diverse phenomena. For example, the increase in rotational speed of a spinning figure skater as the skater's arms are contracted is a consequence of conservation of angular momentum. Procedure 1 Place a student on the swivel office chair 2 Give the student two hand weights, and tell the student to extend his or her arms. 3 Spin the student slowly. On command, have the student bring the two weights to his or her chest. The student s rotation rate will dramatically increase. Tell the student to extend the weights again, and the rotation rate will decrease. Discussion: Let s say that the weights, when extended, follow a circle that has a circumference of five meters. When the weights are brought inward, the circle has a circumference of one meter. Finally, let s say that you start the student rotating, with weights extended, at a rate of one rotation per second. (Of course, this is a very fast rotation rate but using whole numbers makes it easier to understand what is happening.) During a single rotation, the weights will travel a distance of five meters. Their angular velocity is five meters per second. When the weights are brought inward, the rotation rate increases to five times per second, but with a circumference of one meter, the weights are still traveling five meters per second! When the weights go back out, the rotation rate drops but not the angular velocity. df 75

80 Forces and Motion 76

81 Forces and Motion Bulls Eye! Passport question: What forces act on the marble? Passport answer: Gravity and horizontal movement Background information: Engineers and Scientists with NASA often have to get information about planets, stars, and space without actually putting a person there. This is when NASA must remotely deploy machines to land and take samples. The first challenge that comes with this is a correct landing. Theree are many forces that would prevent a robot from landing on the correct spot or bull s eye. In this activity students will pretend to be a NASA scientist that is remotely deploying a rover, it is a competition to see who can most effectively land on the bull s eye. Procedure Have a student pick a marble vessel they will use. Ask them to hypothesize how they plan on getting the marble on the bull s eye. Put the marble in and attach it to the string Make sure to have a student or volunteer bee the judge of where the marble lands Let the student release the marble with their goal to hit the bulls eye marked on the floor Measure the distance from the center of the bulls eye to where the marble landed Record the name of the student and the distance (only top ten on board) If time permits, let them try again see if theirr hypothesis was correct or incorrect Discussion: When deploying the marble there are manyy forces acting on it thatt may prevent it from landing on the bull s eye. The marble is already moving horizontally when it is deployed. Gravity then begins to act on it pulling it toward the ground. When an object that is already moving horizontally is dropped (like a marble dropped from a cup moving down a zip line), it travels in a curved path, called a trajectory. That is why students can t deploy right over the bull s eye because it will still have horizontal force. 77

82 Forces and Motion 78

83 Forces and Motion Physicss Fear Factor Passport question: When the tennis ball is held up what kind of energy does it have? Passport answer: Potential Energy Background information: Energy can be converted from potential energy (stored energy) to kinetic energy (energy of motion). A pendulum is a perfect example of the conservation and conversion of energy. Because no energy (or force) is added to the system, a pendulum will swing evenly over an equilibrium point returning to the same point each time. Procedure (this can be done with volunteers or students) 1 Place volunteer/student against a wall, tell them not to move and to keep their head back on the wall 2 Hold the tennis ball a inch or so away from their nose 3 Let go of the ball, DO NOT THROW/PUSH just simply let it leave your hand Discussion: As long as you do not move your head, the ball will not hit you, even if we used something really heavy like a bowling ball! Why not? As the ball moves away from you, it is picking up speed. It is converting potential energy, from its height, into kineticc energy, the energy of motion. Once it passes the lowest point, the opposite begins to happen. It is now moving against gravity, and some of its kinetic energy is converted into potential energy. Once all of the kinetic energy has been converted, it stops and starts to move downwards again. In a perfect system, this would keep happening over and over, with no energy lost. This is Newton s first law; every object in a state of uniform motion tends to remain in that state of motion 79

84 Forces and Motion unless an external force is applied to it. In reality, there is resistance from the air, friction with the string, all sorts of things to drain away some of the energy. This means that each swing will not go quite as high as the one before it. Because we know that our ball on a string system is not perfectly frictionless, we know that the ball will not make it back up high enough to hit your face. 80

85 Forces and Motion Passport question: Why do compasses point north? Passport answer: Because the compass is made from a temporary magnet and is attracted to the Earth s magnetic field Background information: Magnetism- A property of certain kinds of materials that causes them to attract iron or steel Ferromagnetic- The property of being strongly attracted too either pole of a magnet. Ferromagnetic materials, such as iron, contain unpaired electrons, each with a small magnetic field of its own, that align readily with each other in responsee to an external magnetic field. Magnet- objects that produce magnetic fields and attract metals like iron, nickel and cobalt. The magnetic field's lines of force exit the magnet from its north pole and enter its south pole. Permanent magnets - create their own magnetic field all the time. Temporary magnets- produce magnetic fields while in the presence of a magnetic field and for a short while after exiting the field. Magnet Mania! Procedure A (General Investigation) 1 Have students investigate what materials aree or are not magnetic 2 Have students investigate how magnets interact (repel, attract, different with distance) 3 Have students play with the hot wheels with magnets 4 Have students investigate magnets with iron fillings 5 Discuss their findings Discussion: Items that become stick to magnets are ferromagnetic materials; they become temporary magnets themselves and can have other magnets or ferromagneticc materials stick to them. Connecting north to south ends of small magnets can make one largee magnet as seen below. 81

86 Forces and Motion Procedure B (Paperclip on a leash) 1 Have student bring magnet close to the paperclip on a leash but do not allow the paperclip to come in contact with the magnet 2 Pass an index card through the gap between the magnet and the paperclip Discussion: While observing the properties of electromagnetic fields were you actually able to see the energy? No, because the force is a result of electrons repelling and attracting one another and it is too small to see. As you may have noticed will passing the index card in between the magnet, electromagnetic fields have the ability to go through solid objects. Procedure C (Make a Compass) 1 To magnetize needle rub one end of the needle with the north pole of the magnet 50 times. Mark this end with a red sharpie 2 Repeat rubbing the south end of your magnet against the non-magnetized end of the sewing needle 3 Thread the needle through the circle of wax paper as you would needle into cloth. Do not run the needle all the way through, but leave the needle half-way through the wax paper with the needle lying flat on the surface of the wax paper. 4 Float the wax paper with needle on the surface of water, The ends of the needle should be facing up with the middle of needle, on the underside of the wax paper, facing the water. 5 The needle will act like a compass, the north end facing to the north pole Discussion: We are able to make the needle into a magnet by rubbing it, this induces magnetism and the needle becomes a temporary magnet. This is how people found their way before the days of GPS. Imagine being on a boat in the middle of the ocean with nothing for reference, a compass allowed people to travel successfully. The reason why a compass works is more interesting. It turns out that you can think of the Earth as having a gigantic bar magnet buried inside. In order for the north end of the compass to point toward the North Pole, you have to assume that the buried bar magnet has its south end at the North Pole, as shown in the diagram at the right. If you think of the world this way, then you can see that the normal "opposites attract" rule of magnets would cause the north end of the compass needle to point toward the south end of the buried bar magnet. So the compass points toward the North Pole. 82

87 Forces and Motion 83

88 Forces and Motion 84

89 Forces and Motion Eddy Currents Passport Question: Does a magnet fall faster in a a) metal tube b) plastic tube? Passport Answer: a) metal tube Background Information: When current is induced in a conductor the induced current often flows in small circles that are strongest at the surface and penetrate a short distance into the material. These current flow patterns are thought to resemble eddies in a stream, which are the tornado looking swirls of the water that we sometimes see. Because of this presumed resemblance, the electrical currents were named eddy currents. These eddy currents have their own magnetic field that opposes the magnetic field. Because of the tendency of eddy currents to oppose, eddy currents cause energy to be lost. More accurately, eddy currents transform more useful forms of energy, such as kinetic energy, into heat, which is generally much less useful. Procedure 1 1 Hold the metal tube vertically. Drop the magnet through the tube 2 Hold to the metal tube vertically. Drop the nonmagnetic object through the tube 3 Make observations about the speed of the fall 4 Hold the PVC tube vertically. Drop the magnet through the tube 5 Hold the PVC tube vertically. Drop the nonmagnetic object through the tube 6 Make observations about the speed of the fall Discussion: What is happening? As the magnet falls, the magnetic field around it constantly changes position. As the magnet passes through a given portion of the metal tube, this portion of the tube experiences a changing magnetic field, which induces the flow of eddy currents in an electrical conductor, such as the copper or aluminum tubing. The eddy currents create a magnetic field that exerts a force on the falling magnet. The force opposes the magnet's fall. As a result of this magnetic repulsion, the magnet falls much more slowly. 85

90 Forces and Motion Procedure 2 1 Swing the copper plate between the magnets on the pendulum 2 Swing the copper plate without magnets on the pendulum 3 Observee the difference The eddy current slows the pendulum down. 86

91 Forces and Motion How Does this Stack Up? Passport Question: What physics concept are you manipulating so the blocks don t fall over? Passport Answer: The center of gravity of an object Background Information: In physics, the center of gravity of an object is the average location of its weight. In a uniform gravitational field, it coincides with the objects center of mass Gravity is the invisible force that causes objects to pull toward each other. In the world around us, we can best explain gravity by letting things drop to the floor or ground. Gravity pulls objects and people toward the earth. That is why things fall to the ground, and also why people and objects don't just float around in the air. The center of gravity is the factor that keeps people and objects balanced. It is the average place of the entiree weight of a person or a thing. Procedure Stack the blocks evenly on top of one another to make a vertical column Position the stack so that you are facing the long side off the blocks Start at the top of the stack. Move the top block to the right so it overhangs the second block as far as possible without falling. Now move the top two blocks to the right ass a unit so they overhang the third block as far as possible without falling. Move the top three blocks, and continue on down the stack. Discussion: How many blocks must you move before the top block is completely beyond the balance point? Notice that you can never move a given block over as far as you moved the previous one. The larger the stack of blocks you are moving, the smaller thee distance you can move them beforee they become unbalanced and topple over. 87

92 Forces and Motion When you move the top block over so that it just balances, its center of gravity, or balance point, rests over the edge of the block below. Each time you move a block over, you are finding the center of gravity of a new stack of blocks - the block you move plus the blocks above it. The edge of each block acts as a fulcrum supporting all the blocks above it. By considering the positions of the centers of gravity of the blocks as the stack is built, it can be shown that the first block will be moved 1/2 of a block length along the second block, the top two blocks will be moved 1/4 of a block length along the third block, the top three blocks will be moved 1/6 of a block length along the fourth block, the top four blocks will be moved 1/8 of a block length along the fifth block, and so on. Do you see the pattern? 88

93 Forces and Motion Loony Balloons Passport Question: Why does the balloon take such a strange trajectory? Passport Answer: the water filled balloon is causing the air balloon to change its center of gravity. Background Information: The center of gravity is the average location of the weight of an object. The center of gravity, if an object doesn t change shape will be constant. If an object changes shape or weight distribution its center of gravity will change. Inertia is the tendency of an object to keep moving in the same direction. Procedure 1 Pour a little bit of water into one of the balloons and tie the neck. 2 Squeeze and push the small water-filled balloon into the empty balloon. 3 Blow into the outside balloon and tie the neck so that the little water-filled balloon is inside the outer inflated balloon. 4 Toss the balloon to someone else, or throw the balloon up in the air and catch it 5 Ask the kids to watch, and explain the motion of the Loony Balloon Discussion: The balloon wobbles as the water-filled balloon rolls around inside. An inflated balloon has little mass compared to the water-filled balloon inside it. When the water-filled balloon inside the inflated balloon is put into motion, the inertia (the tendency to keep moving in the same direction) of the water-filled balloon overpowers the balloon s motion and causes eccentric behavior. The eccentric behavior of the balloon can also be linked to the changing center of gravity of the balloon. The center of gravity is the average location of the weight of an object. As the inner balloon moves, so does the average weight, which causes the balloons to loop. The balloon moves oddly to the viewer who cannot see the motion of the inner water-filled balloon. Gravity also pulls the water-filled balloon, which causes it to travel downward at an unexpected speed. When the water-filled balloon and the inflated balloon move, they act as a system. 89

94 Forces and Motion 90

95 Forces and Motion Gravity Keeps You Down Passport Question: What is the force that pulls objects down? Passport Answer: Gravity Background Information: All objects (regardless of their mass) experience the same acceleration when in a state of free fall. When the only force is gravity, the acceleration is the same value for all objects. On Earth, this acceleration value is 9.8 m/s/s. This is such an important value in physics that it is given a special name - the acceleration of gravity - and a special symbol - g. This said, and elephant and a feather with the absence of air resistance should fall at the same rate and hit the ground at the same time. Air resistance, also called drag, refers to forces that oppose the relative motion of an object through a fluid, liquid, or gas. These forces act in a direction opposite to the oncoming flow velocity. When an object is falling air resistance acts to push it back up. This is only true for objects falling straight down. If the object was falling left or right, then air resistance would be opposite. Air resistance is the opposite of gravity for an object falling down. It pushes up while gravity pushes down. Size and shape are the two factors that affect air resistance. Air resistance works with surface area, so the more surface area, the more air resistance. Procedure 1 Do a demo with the feather and book. 1) Drop the feather and book separately. Note that it takes the feather longer to reach the ground than the book. 2 Ask the students why this is. (answer air resistance) 3 Ask the students if they can figure out a way to drop the feather and book at the same rate (answer: put the feather on top of the book, this blocks the air resistance for the feather) 4 Let the students experiment with gravity and air resistance using newspaper. See how it falls flat, crumpled loosely, crumpled tightly, etc. 91

96 Forces and Motion Discussion: This experiment will help the students learn that without air resistance all objects will fall at the same rate. In physics we often talk about a vacuum. This is a space with no matter, no air that can resist movement. These vacuums do not exist in nature, and perfect vacuums are impossible to produce, but partial vacuums get close. Air resistance is what makes objects fall at different rates, the more surface area and drag an object has the slower it will fall. Think about a sky diver with or without a parachute, how fast they fall is drastically different. 92

97 Forces and Motion Spinnin g the bucket Passport Question: What circular force keeps the water in the bucket? Passport Answer: centripetal force Background information: This classic experiment shows the how different forces actt on one system. 1) Gravity- which is the force pulling everything down and 2) centripetal force- which pulls the bucket and the water into the center of the rotation made by spinning the bucket, centripetal force is a center seeking force which means that the force is always directedd toward thee center of the circle. Without this force, an object will simply continue moving in straight line motion Procedure Ask the student what happens if they put a bucket of water upside down over their head? It will spill Ask the student how they can stop the water from spilling, continue with the experiment Fill the bucket three quarters of the way with water Take the bucket by the handle and start spinning it around at your side from the ground, up to the sky,, turning your arm behind you as the bucket makes it way back down towards the ground. Keep the speed and motion of rotation the same Discussion: It seems as if the water in the bucket is defying gravity, but is it really? No. Gravity - the force pulling down on everything - is still at work even when thee bucket and water are above your head. The water's inertia wants to keep the water traveling in a straight path, but gravity is acting on the water, causing it to fall in a downward pathh that will eventually hit the earth. 93

98 Forces and Motion However, while the water is falling, the bucket is falling with it, catching the water. What keeps the bucket and water moving in a nice circular path that doesn't get wet or messy is the string. The spinning of the bucket acts as the centripetal force that pulls the bucket and water into the center and keeps them from following their paths of inertia, giving the illusion that centrifugal force is pulling the water away from the center. The person spinning the bucket will be spared a soaking as long as the bucket moves fast enough so the centripetal force is greater than the force of gravity. But be careful! In order for the bucket to keep falling with the water, the bucket must travel fast enough to keep up with the water. If you spin the bucket too slowly, the water will fall out and you will get wet. 94

99 Forces and Motion Audible Acceleration Passport Question: What causes falling objects to accelerate? Passport Answer: Gravity Background information: Velocity = change in distance / change in time Acceleration = change in velocity / change in time Gravity accelerates all objects at the same rate (regardless of mass) Without friction, objects will falll at 9.8m/s^2, that means increase by 9.8 meters per second every second. This acceleration is hard to see with the naked eye; scientists often use a slow-motion camera to calculate the acceleration due to gravity. We will use sound to recognize that objects accelerate when they fall. Procedure There are two strings, one with evenly spaced washers and one with washers spaced out 0cm, 30 cm, 130 cm, and m from the floor The bottom washer should be touching the ground (in the metal pan) for both strings Let go of the evenly spaced string (sounds of the washers should be uneven time intervals) Let go of the unevenly spaced (sounds of thee washers should be even time intervals) Discussion: The string with evenly spaced washers will not land at evenly spaced times, because the washers accelerate due to gravity. The washer at the very top of the string will land on the metal pan at a higher velocity than the washer at the bottom of the stringg because it had more time to accelerate due to gravity. 95

100 Forces and Motion The string with unevenly spaced washers (0cm, 30cm, 130cm, and 2.74m) will land at evenly spaced intervals because the way they were spaced out took into account the acceleration due to gravity. 96

101 Forces and Motion Mystery Candle Passport Question: What happened to the air in the vase when the candle went out? Passport Answer: It got colder and it contracted because cold air contracts Background Information: When air is heated up it expands and when air is cooled it contracts. For example, on a really cold day your car s tires may look flat because the air is cold and has contracted and is exerting less pressure on its container, the tire. If air is not contained the change in pressure from temperature change can go unnoticed. This experiment will let us see the change in pressure from heat change. Procedure 1 Fill a plastic cup up with water. About 9 oz. 2 Add 2 or 3 drops of food coloring to the water. This will make the movement of the water easier to see later on in the experiment. 3 Pour the water into the plate or pan and place the candle in the middle of the water. 4 Light the candle. 5 Cover the candle with the vase 6 Have the students think about what is taking place both inside and outside of the vase. What invisible thing is inside the vase? 7 Have the students carefully observe what happens to the water around the vase. It's bubbling! What happens to the candle flame? Discussion: The candle flame heats the air in the vase, and this hot air expands. Some of the expanding air escapes out from under the vase you might see some bubbles. When the flame goes out, the air in the vase cools down and the cooler air contracts. The cooling air inside of the vase creates a vacuum. This imperfect vacuum is created due to the low pressure inside the vase and the high pressure outside of the vase. We know what you're thinking; the vacuum is sucking the water into the vase right? You have the right idea, but scientists try to avoid using the term "suck" when describing a vacuum. Instead, they explain it as gases exerting pressure from an area of high pressure to an area of low pressure. A common misconception regarding this experiment is that the consumption of the oxygen inside of the bottle is also a factor in the water rising. Truth is, there is a possibility that there would be a small rise in the water from the flame burning up oxygen, but it is extremely minor compared to the expansion and contraction of the gases within the bottle. Simply put, the water would rise at a steady rate if the oxygen being consumed were the main contributing factor (rather than experiencing the rapid rise when the flame is extinguished). 97

102 Forces and Motion 98

103 Forces and Motion Balloon in a Bottle Passport Question: How do you know air takes up space? Passport Answer: Because you can t blow up the balloon without a hole in the bottle Background information: We can t see air, but we know it is there. How? Air exerts takes up space and exerts pressure. Procedure 1 Slip the balloon through the neck of the bottle. 2 Stretch the opening of the balloon around the mouth of the bottle. 3 Try to inflate the balloon by blowing into it, it won t inflate very much 4 Punch a small hole (about the size of a nail) into the bottom of the bottle 5 Repeat steps one through three. Discussion: When we put the balloon inside the bottle there was already air in there taking up space. The air is trapped in the bottle and couldn t get out; therefore you cannot make the balloon any bigger. But once we poke a hole in the bottom of the bottle the air that was formerly trapped can escape and the student can successfully blow up the balloon. 99

104 Forces and Motion 100

105 Forces and Motion The Power of Words Passport Question: How much atmospheric pressure is exerted on you at all times? Passport Answer: 14.7 pounds per square inch Background information: Atmospheric pressure is the force exerted on you by the weight of tiny particles of air. Earth's atmosphere is pressing against each square inch of you with a force of 14.7 pounds per square inch. So, the more surface area something has, the more atmospheric pressure is exerted onto it. Procedure 1 Lay the ruler over the edge of the table so that it is about 1/3 of its length is over the edge 2 Ask the students what they think will happen if you hit the ruler from above. 3 Hit the ruler, as expected it flips off the table. 4 Ask the students how you might possibly keep the ruler on the table while you hit it, using only newspaper. Hopefully someone will guess that you need to exert an opposing force on the far end of the ruler you may need to prompt them. 5 Tell the students that you can only use one sheet of newspaper. 6 Try first by folding up a sheet of newspaper as small as possible and placing it at the back end of the ruler so that it acts as a counterweight. Get an audience member to hit the ruler again still it flips off the table, this time along with the folded up newspaper! 7 Ask the students how else you might be able to use a sheet of newspaper to hold the ruler down. If a student gets the trick, ask them to explain the physics behind the idea. 8 Lay a single sheet of newspaper flat on the table so that the ruler is roughly in the center. When you hit the ruler it will stay on the table! For optimal effect, make sure as little air as possible is under the newspaper by smoothing it out flat prior to hitting the ruler. Discussion: How does this work? It all comes down to air pressure. Atmospheric pressure is exerting a downward force on the single sheet of newspaper. The area of a single sheet of newspaper is fairly large; therefore the downward force of the atmospheric pressure exerted on the newspaper is strong enough to counter the upward force of hitting the ruler. It didn't work with 101

106 Forces and Motion the folded-up newspaper because the surface area over which the atmospheric pressure could act was far too small. or 102

107 Forces and Motion Automatic Balloon Inflator Passport Question: Does hot air or cold air take up more space? Passport Answer: hot air takes up more space Background information: We can t see air, yet it is all around us. Air takes up space and can expand and contract. During this experiment we will see what happens to air iff it is heated up or cooled down. Procedure Set up 1 bottle with a balloon on top Ask students what they think will happen if you put the bottle in the hot or cold water Test their hypothesis: Put the bottle in the hot water, it will expand Let the balloon shrink back slowly in room temperature Put the balloon in the hot water again, it will expand Quickly transfer the bottle from the hot water to the cold water and see that the balloon shrinks at a faster rate than in room temperaturee air Discussion: As seen in the above picture, the pressure exerted byy the gas is directly related to the temperature. The higher temperature the more pressure exerted. This is because higher temperatures excite the molecules. The faster the air atoms go,, the more energy they have with which to do work and push against their surroundings. This energy is kinetic energy, the energy of motion. The more heat exposed to a gas, the more kinetic energy. 103