Conducting Energy and Heat. Energy Likes to Move. Radiating Energy

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1 Energy Likes to Move If there is a temperature difference in a system, heat will naturally move from high to low temperatures. The place you find the higher temperature is the heat source. The area where the temperature is lower is the heat sink. When examining systems, scientists measure a number called the temperature gradient. The gradient is the change in temperature divided by the distance. The units are degrees per centimeter. If the temperature drops over a specific distance, the gradient is a negative value. If the temperature goes up, the gradient has a positive value. The greater the gradient, the more energy will be exchanged. Ever Hear of Convection Ovens? Convection is the way heat is transferred from one area to another when there is a "bulk movement of matter." It is the movement of huge amounts of material, taking the heat from one area and placing it in another. Warm air rises and cold air replaces it. The heat has moved. It is the transfer of heat by motion of objects. Convection occurs when an area of hot water rises to the top of a pot and gives off energy. Another example is warm air in the atmosphere rising and giving off energy. They are all examples of convection. The thing to remember is that objects change position. Radiating Energy When the transfer of energy happens by radiation, there is no conductive medium (such as in space). That lack of medium means there is no matter there for the heat to pass through. Radiation is the energy carried by electromagnetic waves (light). Those waves could be radio waves, infrared, visible light, UV, or Gamma rays. Heat radiation is usually found in the infrared sections of the EM spectrum. If the temperature of an object doubles (in Kelvin), the thermal radiation increases 16 times. Therefore, if it goes up four times, it increases to 32 times the original level. Scientists have also discovered that objects that are good at giving off thermal radiation are also good at absorbing the same energy. Usually the amount of radiation given off by an object depends on the temperature. The rate at which you absorb the energy depends on the energy of the objects and molecules surrounding you. Conducting Energy and Heat Conduction is a situation where the heat source and heat sink are connected by matter. As we discussed before, the heat flows from the source down the temperature gradient to the sink. It is different from convection because there is no movement of large amounts of matter, and the transfers are through collisions. The source and the sink are connected. If you touch an ice cream cone, the ice cream heats up because you are a warmer body. If you lie on a hot sidewalk, the energy moves directly to your body by conduction. When scientists studied good thermal radiators, they discovered that good thermal conductors are also good at conducting electricity. So when you think of a good thermal conductor, think about copper, silver, gold, and platinum.

2 Getting Hotter = Getting Bigger Now you need to think about states of matter a little bit. We'll start with gases. The idea behind thermal expansion is that gases expand as the temperature increases. If you have a balloon and you heat up the contents, the balloon will get larger. Scientists use the term ideal gas law to describe this activity. Liquids expand and contract, too, but there is a lot less change than in gases. Scientists say they have a smaller thermal expansion coefficient. As you can probably figure out, solids expand and contract the least of all the states of matter. The expansion coefficient is different for each piece of matter. It is a unique value, just like specific heat capacity. Two examples of coefficients are air at and alcohol at Things Shrink When They get Cold The opposite of expansion is contraction. If things expand with the addition of heat, it makes sense that they contract when heat is removed. If you remove enough heat from a gas it will become a liquid. Liquids can turn into solids with further cooling. What happens when you remove almost all of the energy from a system? Scientists use the terms absolute zero to describe a system that has no kinetic energy. When there is no kinetic energy in a system, all molecular motion stops. It seems that even the atoms begin to merge at these low temperatures. Physicists have recently created the Bose-Einstein state of matter that has a small group of atoms with nearly all of the kinetic energy taken out of the system.

3 1. Read It! Heat moves from a temperature to a temperature. 2. Read It! Warm air and cool air. A. Higher; higher A. Rises; remains the same B. Lower; higher B. Sinks; rises C. Higher; lower C. Rises; sinks D. Lower; lower D. Remains the same; sinks Read It! 3. Type of heat transfer that can occur 4. through empty space. A. conduction B. convection C. radiation Read It! Heat transfer that occurs between items that are touching. A. conduction B. convection C. radiation D. transmission D. transmission

4 1. Watch It! Go to the following link and watch the study jams video: Answer the questions on Task Cards 2-7 on your lab sheet in the Watch It! Section. 2. Watch It! What is heat? A. Thermal Energy B. Temperature C. Electricity D. Electromagnetic energy Watch It! Which of the following explains 3. the process of radiation? 4. A. When heat gets transferred through objects that are touching. B. When the measurement of heat in the atmosphere goes down. C. When heat gets transferred through electromagnetic waves that move through space. D. When heat gets transferred through a liquid or a gas. Watch It! How does heat transfer through conduction? A. From the warm object to the cool object B. From the cool object to the warm object C. From the air to the cool object D. From the warm object into the air

5 Watch It! What is the difference between a conductor and an insulator? 5. A. An insulator lets heat pass through it 6. easily; a conductor does not let heat pass through it easily. B. A conductor is unaffected by heat and an insulator is greatly affected by heat. C. A conductor lets heat pass through it easily; an insulator does not let heat pass through it easily. Watch It! Why does the water in a swimming pool stay cool on a hot, sunny day? A. Because radiation has no effect on water B. Because of convection C. Because the pool is a good insulator D. Because the rays of the sun are reflected off of the surface of the water. 7 Watch It! Which method transfers heat through a liquid or a gas? A. conduction B. convection C. radiation D. transmission 1. Organize It! Sort the cards into the three categories; conduction, convection, or radiation. Make sure your teacher checks and initials your lab sheet.

6 1. Explore It! Go to: Find the conduction and convection Gizmo 2. Explore It! There are TWO flasks: one blue and one yellow. ~Select COPPER & Select SOLID CHUNK ~Use the sliders to make one flask ~Click Play hotter than the other. Answer the questions on the LAB SHEET Explore It! 3. Click Reset Set the Initial temperature of the top 4. flask to 95 C and the bottom flask to 5 C. Observe: Run the Gizmo twice once with a Solid chunk of Copper separating the liquids, and once with a Solid chunk of Stone. Explore It! Experiment: Experiment with all six Solid chunks. For each, click Fast forward and then, after about 500 seconds, Pause Record the temperature of each flask. Fill in the data table on your lab sheet under Explore It!

7 1. The transfer of heat through currents is A. Conduction B. Convection C. Radiation 2. A thermos bottle keeps warm liquids warm and cold liquids cold. A thermos bottle must be made from a good A. heat conduction material B. heat insulation material C. heat expanding material D. Transformation D. heat contracting material 3. Materials through which heat can flow easily are called 4. A. insulators B. radiators C. transformers D. conductors When a metal spoon with a temperature of 20 o C is placed into a cup of water with a temperature of 90 o C the spoon will heat up. This is an example of: A. convection B. radiation C. conduction D. insulation

8 5. Two jars are placed inside an insulated box (together). One contains hot soup and the other contains ice water. What will happen to the two liquids? A. Both the hot soup and the ice water will gain heat. 6. When cooking macaroni and cheese, the noodles float up to the top and sink back down. This is an example of: A. convection B. Both the hot soup and the ice water will lose heat. C. The hot soup will gain heat and the ice water will lose heat. B. conduction C. radiation D. insulation D. The hot soup will lose heat and the ice water will gain heat. Four different-colored blocks are placed outside in bright sunlight. The 7. blocks are identical except for color. 8. The diagram below shows the amount of light reflected from each block. Which block would heat up the fastest? A. Block 1 B. Block 2 C. Block 3 D. Block 4 During a house fire, the smoke and flames rise up, but the air down near the floor is cooler and less smoky. This is an example of: A. conduction B. convection C. radiation D. insulation

9 Research It! Research It! 1. Heat is transferred by radiation from the sun to the Earth. Why do coastal (located near ocean) communities have cooler 2. What type of heat transfer causes the movement of Earth s tectonic plates? How? summers and warmer winters? Write It! 1. What type of heat 2. transfer is involved in cooking an egg. Describe the heat transfer processes from start to finish. Write It! You took a can of soda out of the fridge. After holding it for a few minutes, what has happened to the temperature of the can? What has happened to the temperature of your hand? Why? Describe the process(es) that have taken place.

10 Illustrate It! Illustrate It! 1. Draw a diagram of conduction. Use red arrows to show the direction the thermal is moving. 2. Draw a diagram of radiation. Use squiggly red arrows to show the direction the thermal energy is moving. Illustrate It! BONUS 3. Draw a diagram of 1. convection. Use red arrows to represent high temperature and blue arrows to represent a low temperature. Write a story about thermal energy s long journey from the sun. How long does it take light and heat to reach Earth? What happens during this journey?

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14 Through Space Cooler downstairs than upstairs Direct contact Movement through a fluid Collision of atoms

15 Name: Class: Date: Task Card 2: Input Stations Explore It! Connection Initial temp. (top flask) Initial temp. (bottom flask) Solid copper 95 C 5 C 500 sec. temp. (top flask) 500 sec. temp. (bottom flask) Use the sliders to make one flask hotter than the other. Click play. What happens? Select the DATA tab and look at the graph. What do the blue curve and the yellow curve represent? Solid gold 95 C 5 C Solid lead 95 C 5 C Solid stone 95 C 5 C Solid glass 95 C 5 C A. The blue curve represents Solid rubber 95 C 5 C B. The yellow curve represents C. What is the final temperature of the top flask? D. What is the final temperature of the bottom flask? Task Card 3: Observe: Run the Gizmo twice once with a Solid chunk of Copper separating the liquids, and once with a Solid chunk of Stone. Watch how quickly the temperatures of the liquids change in both cases. (Note: This solid chunk keeps the liquids from mixing.) Form hypothesis: A conductor allows heat to flow easily, while an insulator resists heat flow. In general, what kinds of materials do you think are good conductors? Predict: Of the six substances in the Gizmo, which ones will allow the Analyze: What substances conducted heat the best? How do you know? Draw conclusions: What do the best conductors have in common? Read It! fastest temperature change in the two flasks? Task Card 4: Watch It!

16 Output Stations: Write It! Output Stations Illustrate It Task Card 1: Task Card 1: Task Card 2: Task Card 2: Task Card 3: Task Card 4: Organize It! Teacher Initials: Reflection: How did you do? What did you find easy? What mistakes did you make?