A D V A N C E D P H Y S I C S C O U R S E C H A P T E R 5 : W O R K, E NERGY AND POW ER

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1 A D V A N C E D P H Y S I C S C O U R S E C H A P T E R 5 : W O R K, E NERGY AND POW ER FOR HIGH SCHOOL PHYSICS CURRICULUM AND ALSO THE PREPARATION OF ACT, DSST, AND AP EXAMS This is a complete video-based high school physics course that includes videos, labs, and hands-on learning. You can use it as your core high school physics curriculum, or as a college-level test prep course. Either way, you ll find that this course will not only guide you through every step preparing for college and advanced placement exams in the field of physics, but also give you in hands-on lab practice so you have a full and complete education in physics. Includes text reading, exercises, lab worksheets, homework and answer keys. BY AURORA LIPPER SUPERCHARGED SCIENCE Supercharged Science Page 1

2 TABLE OF CONTENTS Material List... 4 Introduction... 5 What is Energy?... 6 What is Work?... 7 Units for Energy... 8 Moving Against a Force... 9 Energy of Food Bomb Calorimeter Back to work! Work done by Friction How much work in climbing stairs? Non-conservative Forces Kinetic Energy Bow and Arrow Problem Freefall Pennies Potential Energy Elastic Energy Energy Transforms WackaPOW! Power Power is Scalar What size engine do you need? Work-Energy Relationship Mechanical Energy Relationship Energy Exchange between Kinetic and Potential Energy Inclined Plane Energy Exchange Elastic Potential Energy Pendulums and Energy Transfer Potato Cannon Bobsleds Roller Coasters Supercharged Science Page 2

3 Including Friction in your Calculations Springs Springs and the Conservation of Energy Car Suspension Problem Elevator Nightmare Speedy Waterslide Gravity Go-Karts Shooting the Sand Friction Energy Driving with Physics in Mind Light Speed Particles Homeowrk Problems with Solutions Supercharged Science Page 3

4 MATERIAL LIST While you can do the entire course entirely on paper, it s not really recommended since physics is based in real-world observations and experiments! Here s the list of materials you need in order to complete all the experiments in this unit. Please note: you do not have to do ALL the experiments in the course to have an outstanding science education. Simply pick and choose the ones you have the interest, time and budget for. Several balls of different weights (golf ball, racket ball, ping pong ball, marble etc. are good choices) Mixing bowl Flour, corn starch, or any kind of light powder Apple Meter or yardstick Shelled peanut Small pair of pliers Match or lighter Rubber band Toy cars (or anything that rolls like a skate) A board, book or car track Measuring tape Short dowel or cardboard tube from a coat hanger Tape Can with a lid Heavy rock or large nut 2 paper clips String A washer or a weight of some kind Set of magnets (at least 6, but more is better) Potatoes Clear, strong plastic (like acrylic) tube Wooden dowel Washer (this is your hand-saver ) Aluminum foil Marbles (at least four the same size) Long tube (gift wrapping tube or the clear protective tube that covers fluorescent lighting is great) Masking tape 3/4 pipe foam insulation (NOT neoprene and NOT the kind with built-in adhesive tape) Note: Materials for Gravity Go-Karts is listed with the experiment itself. Please watch video for shopping list and material specifications Supercharged Science Page 4

5 INTRODUCTION Energy is the mover and shaker of the universe. Heat from the Sun, sounds from your radio, riding a bike and watching a movie are all expressions of different forms of energy. As you sit there reading this, there is energy flowing all around you in the form of light waves, sound waves, radio waves, heat and more. You are constantly being bombarded by energy. Energy is everywhere, all the time. The physics problems we ve solved on paper so far have made good use of Newton s Laws of Motion to figure out how a parachutist falls, how fast the airplane goes, or how high a pitcher throws the baseball. But sometimes, Newton s Laws of Motion break when we apply them to certain problems, such as particles moving near the speed of light, or describing the motion of an electron in an atom. Since there s more than one way to climb a mountain, we re going to look at solving physics problems using energy. Physicists are kind of strange sometimes they ll spend more time figuring out a faster way to solve the problem if it s neater, slicker, and more fun to do. Which is where this new model of looking at the energy transfer between objects comes in. We re going to look at the different forms of energy and how it changes to figure out the same sorts of things we did with Newton s Laws of Motion, so now you ll have two different ways to solve the same problem. This is important because sometimes, you can t use Newton s Laws because you have too many unknown variables (thus making the problem unsolvable), but if you come at the problem from the Energy side, everything works out (and sometimes the math is easier too!). Be sure to take out a notebook and copy down each example problem right along with me so you take good notes as you go along. It s a totally different experience when you are actively involved by writing down and working through each problem rather than passively sitting back and watching Supercharged Science Page 5

6 WHAT IS ENERGY? Energy is the ability to do work. Work happens when something moves a distance against a force. Although it seems a little hard to comprehend, this is truly one of the most useful concepts in physics. I m willing to bet you spend a lot of your time moving things a distance against a force. Do you ever climb stairs, walk, ride a bicycle, or lift a fork to your mouth to eat? Of course you do. Each one of those things requires you to move something a distance against a force. You re using energy and you re doing work Supercharged Science Page 6

7 WHAT IS WORK? Work is not that hard it s force that can be difficult. Imagine getting up a 10-step flight of stairs without a set of stairs. Your legs don t have the strength or force for you to jump up you d have to climb up or find a ladder or a rope. The stairs allow you to, slowly but surely, lift yourself from the bottom to the top. Now imagine you are riding your bike and a friend of yours is running beside you. Who s got the tougher job? Your friend, right? You could go for many miles on your bike but your friend will tire out after only a few miles. The bike is easier (requires less force) to do as much work as the runner has to do. Now here s an important point, you and your friend do about the same amount of work. You also do the same amount of work when you go up the stairs versus climbing up the rope. The work is the same, but the force needed to make it happen is much different. Don t worry if that doesn t make sense now. As we move forward, it will become clearer. Before we start solving physics problems, we first have to accurately define a couple of terms we re going to be using a lot that you might already have a different definition for. Here are three concepts we re going to be working with in this section: Work Energy Power Energy is the ability to do work. Work is done on an object when a force acts on it so the object moves somewhere. It can be a large or small displacement, but as long as it s not in its original position when it s done, work is said to be done on the object. An example of work is when an apple falls off the tree and hits the ground. The apple falls because the gravitational force is acting on it, and it went from the tree to the ground. If you carry a heavy box up a flight of stairs, you are doing work on the box. An example of what is not work is if you push really hard against a brick wall. The wall didn t go anywhere, so you didn t do any work at all (even though your muscles may not agree!). Mathematically, work is a vector, and is defined as the force multiplied by the distance like this: W = F d If there s an angle between the force and displacement vectors, then you ll need to also multiply by the cosine of the angle between the two vectors. This is an important concept: Notice that the force has to cause the displacement. If you re carrying a heavy box across the room (no stairs) at a constant speed, then you are not doing work on the box. The box is traveling in the horizontal direction at a constant speed. You are holding the heavy box up in the vertical direction. The force you are applying to the box is not causing it to be displaced in the same direction. There has to be a component of the force in the horizontal direction if you re doing work on the box ((Remember F=ma? Constant speed means no acceleration!) Mathematically, the work equation would have angle between the force and the displacement vectors at 90 degrees, and the cosine of 90 degrees is zero, thus cancelling the work out to zero Supercharged Science Page 7

8 UNITS FOR ENERGY We ll cover power in a little bit, but first we need to have a unit of measurement for work. The units for work and energy are the same, but note that energy and work are not the same. (Remember, energy is the ability to do work.) For energy, a couple of units are the Joule (J) and the calorie (cal or Cal). A Joule is the energy needed to lift one Newton one meter. A Newton is a unit of force. One Newton is about the amount of force it takes to lift 100 grams or 4 ounces or an apple. It takes about 66 Newtons to lift a 15-pound bowling ball and it would take a 250-pound linebacker about 1000 Newtons to lift himself up the stairs! So, if you lifted an apple one meter (about 3 feet) into the air you would have exerted one Joule of energy to do it. The calorie is generally used to talk about heat energy, and you may be a bit more familiar with it due to food and exercise. A calorie is the amount of energy it takes to heat one gram of water one degree Celsius. Four Joules are about one calorie. A 100-gram object takes about one Newton of force to lift. Since it took one Newton of force to lift that object, how much work did we do? Remember work = force x distance so in this case work = 1 Newton x 20 meters or work = 20 Joules Supercharged Science Page 8

9 MOVING AGAINST A FORCE You may ask, But didn t we move it 40 meters, 20 meters up and 20 down? That s true, but work is moving something against a force. When you moved the object down you were moving the object with a force, the force of gravity. Only in lifting it up are you actually moving it against a force and doing work. Four Joules are about 1 calorie, so we did 5 calories of work. Wow, I can lift an apple 20 times and burn 5 calories! Helloooo weight loss! Well not so fast there Richard Simmons. When we talk about calories in nutrition we are really talking about kilo calories. In other words, every calorie in that potato chip is really 1000 calories in physics. So as far as diet and exercise goes, lifting that apple actually only burned.005 calories of energy (rats!). It is interesting to think of calories as the unit of energy for humans or as the fuel we use. The average human uses about 2000 calories (food calories that is, 2,000,000 actual calories) a day of energy. Running, jumping, sleeping, and eating all use calories/energy. Running 15 minutes uses 225 calories. Playing soccer for 15 minutes uses 140 calories. (Remember those are food calories, multiply by 1000 to get physics calories). Everything we eat refuels that energy tank. All food has calories in it and our body takes those calories and converts them to calories/energy for us to use. How did the food get the energy in it? From the sun! The sun s energy gives energy to the plants, and when the animals eat the plants they get the energy from the sun as well. So, if you eat a carrot or a burger you are getting energy from the sun! Eating broccoli gives you about 50 calories. Eating a hamburger gives you about 450 calories! We use energy to do things and we get energy from food. The problem comes when we eat more energy than we can use. When we do that, our body converts the energy to fat, our body s reserve fuel tank. If you use more energy then you ve taken in, then your body converts fat to energy. That s why exercise and diet can help reduce your weight. Did you know that eating a single peanut will power your brain for 30 minutes? 2017 Supercharged Science Page 9

10 What s a Joule? Overview: Energy shows up in all kinds of ways. We ll see how today through a simple lesson. What to Learn: Energy is the ability to do work. You ll get practice playing with units and learning about how we measure energy and the forms it take. Materials Something that weighs around 100 grams or 4 ounces, about the same as an apple A meter or yard stick Lab Time 1. Grab your 100-gram object, put it on a table. 2. Now lift it off the table straight up until you lift it one meter (one yard). 3. Lift it up and down 20 times. 4. Record your observations in the worksheet. Joule Observations 1. Describe the energy in your object before you do anything to it. Is there more than one way to say this, in terms of units? 2. When you move the object over one meter, what are you doing? 3. When you do this 20 times, use math to say how many Joules of work you are doing. 4. How many Joules of work do you do if you lift the apple 50 times? Reading If we wish to talk about energy further, we need to have a unit of measurement. For energy, a couple of units are the Joule and the calorie. A Joule is the energy needed to lift one Newton one meter. A Newton is a unit of force. One Newton is about the amount of force it takes to lift 100 grams or 4 ounces or an apple Supercharged Science Page 10

11 It takes about 66 Newtons to lift a 15-pound bowling ball and it would take a 250-pound linebacker about 1000 Newtons to lift himself up the stairs! So, if you lifted an apple one meter (about 3 feet) into the air you would have exerted one Joule of energy to do it. The calorie is generally used to talk about heat energy, and you may be a bit more familiar with it due to food and exercise. A calorie is the amount of energy it takes to heat one gram of water one degree Celsius. Four Joules are about one calorie. A 100-gram object takes about one Newton of force to lift. Since it took one Newton of force to lift that object, how much work did we do? Remember work = force x distance so in this case work = 1 Newton x 20 meters or work = 20 Joules. You may ask, But didn t we move it 40 meters, 20 meters up and 20 down? That s true, but work is moving something against a force. When you moved the object down you were moving the object with a force, the force of gravity. Only in lifting it up are you actually moving it against a force and doing work. Four Joules are about 1 calorie, so we did 5 calories of work. Wow, I can lift an apple 20 times and burn 5 calories! Helloooo weight loss! Well not so fast there Richard Simmons. When we talk about calories in nutrition we are really talking about kilo calories. In other words, every calorie in that potato chip is really 1000 calories in physics. So as far as diet and exercise goes, lifting that apple actually only burned.005 calories of energy rats. It is interesting to think of calories as the unit of energy for humans or as the fuel we use. The average human uses about 2000 calories (food calories that is, 2,000,000 actual calories) a day of energy. Running, jumping, sleeping, and eating all use calories/energy. Running 15 minutes uses 225 calories. Playing soccer for 15 minutes uses 140 calories. (Remember those are food calories, multiply by 1000 to get physics calories). This web site has a nice chart for more information: Calories used in exercise. Everything we eat refuels that energy tank. All food has calories in it and our body takes those calories and converts them to calories/energy for us to use. How did the food get the energy in it? From the sun! The sun s energy gives energy to the plants, and when the animals eat the plants they get the energy from the sun as well. So, if you eat a carrot or a burger you are getting energy from the sun! Eating broccoli gives you about 50 calories. Eating a hamburger gives you about 450 calories! We use energy to do things and we get energy from food. The problem comes when we eat more energy than we can use. When we do that, our body converts the energy to fat, our body s reserve fuel tank. If you use more energy then you ve taken in, then your body converts fat to energy. That s why exercise and diet can help reduce your weight Supercharged Science Page 11

12 Exercises Answer the questions below: 1. If something has a weight of 2 Newtons and is moved half a meter, how many Joules of energy are used? Show your work. 2. What is the source of all this energy we re working with here? 3. It doesn t count as work when you move the apple back down. Why not? 2017 Supercharged Science Page 12

13 Answers to Exercises: What s a Joule? 1. If something has a weight of 2 Newtons and is moved half a meter, how many Joules of energy are expended? (1 Joule) 2. What is the source of all this energy we re working with here? (the sun) 3. It doesn t count as work when you move the apple back down. Why not? (The force of gravity does the work, not your arm.) 2017 Supercharged Science Page 13

14 ENERGY OF FOOD The energy in a peanut also produces a large amount of energy when burned in a flame, which can be used to boil water and measure energy. We re going to learn how to release the energy inside a peanut and how to measure it. Here s a cool experiment you can do with a single peanut, a paperclip, pliers, and a candle: So did all the energy from the peanut go straight to the water, or did it leak somewhere else, too? The heat actually warmed up the nearby air, too, but we weren t able to measure that easily Supercharged Science Page 14

15 Do Plants Store Energy? Overview: Put your safety goggles on for today s lab, because we re working with fire! You ll be measuring how much energy a peanut holds by setting it aflame. What to Learn: All our energy needs on earth come from somewhere. We cannot make our own food, but plants can. We are all connected to the plants and soils that they grow in because they provide our very basic needs, as well as some of our more modern needs. Materials Goggles 2 shelled peanuts Small pair of pliers Match or lighter Sink Timer Lab Time 1. Today we re working with fire, so follow all special instructions about working with flames today. 2. Close the drain with a sink stopper, and fill the sink with around an inch of water. 3. Put on safety goggles. Using a small pair of pliers, hold the peanut over the sink and ask your adult helper to light the peanut with the lighter until it catches fire. Have your data recorder ready with the timer. 4. Upon ignition (when the peanut is burning by itself and doesn t need the lighter), start the timer and run it until the peanut stops burning. Record the time on the worksheet. The adult remains present for the entire duration that the peanut is one fire. 5. Drop the peanut into the sink once finished to ensure all flames are out. Allow it to cool as you record additional observations in the worksheet and complete the exercises Supercharged Science Page 15

16 Do Plants Store Energy? Data and Observations Peanut Time burned (write in seconds): 1 2 Observations: Does the peanut burn with a clean flame or a sooty flame? What color is the flame? What color does the peanut turn when it burns? 2017 Supercharged Science Page 16

17 Did the size of the peanut change after it had burned for several minutes? Reading A peanut is not a nut, but actually a seed. In addition to containing protein, a peanut is rich in fats and carbohydrates. Fats and carbohydrates are the major sources of energy for plants and animals. The energy contained in the peanut actually came from the sun. Green plants absorb solar energy and use it in photosynthesis. During photosynthesis, carbon dioxide and water are combined to make glucose. Glucose is a simple sugar that is a type of carbohydrate. Oxygen gas is also made during photosynthesis. The glucose made during photosynthesis is used by plants to make other important chemical substances needed for living and growing. Some of the chemical substances made from glucose include fats, carbohydrates (such as various sugars, starch, and cellulose), and proteins. Photosynthesis is the way in which green plants make their food, and ultimately all the food available on earth. All animals and non-green plants (such as fungi and bacteria) depend on the stored energy of green plants to live. Photosynthesis is the most important way animals obtain energy from the sun. Oil squeezed from nuts and seeds is a potential source of fuel. In some parts of the world, oil squeezed from seeds-- particularly sunflower seeds--is burned as a motor fuel in some farm equipment. In the United States and elsewhere, some people have modified diesel cars and trucks to run on vegetable oils. Fuels from vegetable oils are particularly attractive because, unlike fossil fuels, these fuels are renewable. They come from plants that can be grown in a reasonable amount of time. Fossil fuels are nonrenewable fuels because they are formed over a long period of time Supercharged Science Page 17

18 Exercises Answer the questions below: 1. What is the process called where plants get food from the sun? Osteoporosis Photosynthesis Chlorophyll Metamorphosis 2. Where does all life on the planet get its food? 3. List two ways that we could use the energy in a peanut: a. b Supercharged Science Page 18

19 Answers to Exercises: Do Plants Store Energy: 1. What is the process called in which plants get food from the sun? (photosynthesis) 2. Where does all life on the planet get its food? (plants, and the sun) 3. What can people use a peanut s energy for? (fuel for cars, food) 2017 Supercharged Science Page 19

20 BOMB CALORIMETER If you were a food scientist, you d use a nifty little device known as a bomb calorimeter to measure calorie content. It s basically a well-insulated, well-sealed device that catches nearly all the energy and flows it to the water, so you get a much more accurate temperature reading. (Using a bomb calorimeter, you d get Calories of energy from one peanut!) For those of you who have a test tube and a stand, you can do this experiment a little more accurately and calculate the energy of a peanut like this (don t use a wood clothespin like I did make sure you re using glassware or metal equipment!): 2017 Supercharged Science Page 20

21 Peanut Energy Overview: Put your safety goggles on for today s lab we ll be looking at fire again. You ll be measuring how much energy a peanut holds by setting it on fire and measuring an increase in water temperature. What to Learn: All our energy needs on earth come from somewhere. We cannot make our own food, but plants can. We are all connected to the plants and soils that they grow in because they provide our very basic needs, as well as some of our more modern needs. Materials Goggles 2 shelled peanuts Small pair of pliers Match or lighter Test tube in wire test tube holders (these look like pliers that are designed to hold a test tube) Scale Thermometer Lab Time 1. Today we re working with fire, so follow all special instructions provided about working with fire today. 2. Measure your test tube on the scale when it s empty: grams 3. Fill up your test tube with about 10 grams of water and weigh it again: grams 4. Measure the initial temperature of the water: oc 5. Put on safety goggles. 6. Using a small pair of pliers, hold the peanut and ask an adult to light the peanut with the lighter until it catches fire. 7. Upon ignition (when the peanut is burning by itself and doesn t need the lighter), hold the peanut under the water close to the bottom of the test tube until the peanut stops burning. 8. Quickly measure the final temperature of the water: oc 9. Record your results on the worksheet. 10. Allow the peanut to cool as you record your observations and complete the data tables. Let's take an example measurement. Suppose you measured a temperature increase from 20 C to 100 C for 10 grams of water, and boiled off 2 grams. We need to break this problem down into two parts - the first part deals with the temperature increase, and the second deals with the water escaping as vapor Supercharged Science Page 21

22 The first basic heat equation is this: Q = m c T Q is the heat flow (in calories) m is the mass of the water (in grams) c is the specific heat of water (which is 1 degree per calorie per gram) and T is the temperature change (in degrees) So our equation becomes: Q = 10 * 1 * 80 = 800 calories. If you measured that we boiled off 2 grams of water, your equation would look like this for heat energy: Q = L m L is the latent heat of vaporization of water (L= 540 calories per gram) m is the mass of the water (in grams) So our equation becomes: Q = 540 * 2 = 1080 calories. The total energy needed is the sum of these two: Q = 800 calories calories = 1880 calories. Reading Did you know that eating a single peanut will power your brain for 30 minutes? The energy in a peanut also produces a large amount of energy when burned in a flame, which can be used to boil water and measure energy. Peanuts are part of the bean family, and actually grow underground (not from trees like almonds or walnuts). In addition to your lunchtime sandwich, peanuts are also used in woman's cosmetics, certain plastics, paint dyes, and also when making nitroglycerin. What makes up a peanut? Inside you'll find a lot of fats (most of them unsaturated) and antioxidants (as much as found in berries). And more than half of all the peanuts Americans eat are produced in Alabama. We're going to learn how to release the energy inside a peanut and how to measure it. There's chemical energy stored inside a peanut, which gets transformed into heat energy when you ignite it. This heat flows to raise the water temperature, which you can measure with a thermometer. You should find that your peanut contains calories of energy! Now don't panic - this isn't the same as the number of calories you're allowed to eat in a day. The average person aims to eat around 2,000 Calories (with a capital "C"). 1 Calorie = 1,000 calories. So each peanut contains Calories of energy (the kind you eat in a day). Do you see the difference? So did all the energy from the peanut go straight to the water, or did it leak somewhere else, too? The heat actually warmed up the nearby air, too, but we weren't able to measure that. If you were a food scientist, you'd use a nifty little device known as a bomb calorimeter to measure calorie content. It's 2017 Supercharged Science Page 22

23 basically a well-insulated, well-sealed device that catches nearly all the energy and flows it to the water, so you get a much more accurate temperature reading. (Using a bomb calorimeter, you'd get Calories of energy from one peanut!) 2017 Supercharged Science Page 23

24 Peanut Energy Data and Observations Trial # Mass of Water Temperature Increase Heat Energy 1 (calories) (grams) (oc) Sample 10 grams 80 oc = (10 grams) x (1 degree per cal per gram) x 80 (oc) = 800 calories Trial # Mass of Water Boiled Off (grams) Heat Energy 2 (calories) Sample 2 grams =542calories per gram x 2 grams = 1080 calories 2017 Supercharged Science Page 24

25 Trial # Heat Energy 1(calories) Heat Energy 2(calories) Total Energy Produced(calories) Sample 800 cal 1080 cal 1880 Calories 2017 Supercharged Science Page 25

26 BACK TO WORK! We re going to learn how to calculate the amount of work done by forces by looking at how the force acts on the object, and if it causes a displacement. Have you spotted the three things you need to know in order to calculate the work done? Force Displacement Angle between the force and displacement vector (called theta) The easiest way to do this is to show you by working a set of physics problems. So take out your notebook and a pencil, and do these problems right along with me. Here we go! 2017 Supercharged Science Page 26

27 WORK DONE BY FRICTION How do we calculate the work done by friction? Here s a classic problem that shows you how to handle friction forces in your physics problems Supercharged Science Page 27

28 HOW MUCH WORK IN CLIMBING STAIRS? Ever get out of breath while climbing stairs? How much work do you think you did? Let s find out 2017 Supercharged Science Page 28

29 NON-CONSERVATIVE FORCES Work done by friction is never conserved, since it s turned into heat or sound, and we can t get that back. It s a non-conservative force. Other forces like gravity and speed are said to be conservative, since we can transfer that energy to a different form for a useful purpose. When you pull back a swing and then let go, you re using the energy created by the gravitational force on the swing and transforming it into the forward motion of the swing as it moves through its arc. Energy from friction forces cannot be recovered, so we say that it s an external energy, or work done by an external force Supercharged Science Page 29

30 KINETIC ENERGY All the different forms of energy (heat, electrical, nuclear, sound, and so forth) can be broken down into two main categories: potential and kinetic energy. Kinetic energy is the energy of motion. Kinetic energy is an expression of the fact that a moving object can do work on anything it hits; it describes the amount of work the object could do as a result of its motion. Whether something is zooming, racing, spinning, rotating, speeding, flying, or diving if it s moving, it has kinetic energy. How much energy it has depends on two important things: how fast it s going and how much it weighs. A bowling ball cruising at 100 mph has a lot more kinetic energy than a cotton ball moving at the same speed Supercharged Science Page 30

31 BOW AND ARROW PROBLEM Imagine an arrow is shot from a bow and by the time it hits an apple it is traveling with 10 Joules of kinetic energy (kinetic energy is the energy of motion). What s meant by kinetic energy is that when it hits something, it can do that much work on whatever is hit. Soooo, back to the arrow if the arrow hits that apple it can exert 10 Joules of energy on that apple. It takes about 1 Newton of force to move that apple so the arrow can move the apple 10 meters. One Joule equals one Newton x one meter so 10 Joules would equal one Newton x 10 meters. It could also exert a force of 10 Newtons over one meter or any other mathematical calculation you d like to play with there. (This, by the way, is completely hypothetical. With the apple example we are conveniently ignoring a bunch of stuff like the fact that the arrow would actually pierce the apple, and that there s friction, heat, sound, and a variety of other forces and energies that would take place here.) 2017 Supercharged Science Page 31

32 FREEFALL PENNIES Here s a fun experiment that uses a penny in free fall to practice calculating kinetic energy. Energy changes to other forms of energy all the time. The electrical energy coming out of a wall socket transfers to light energy in the lamp. The chemical energy in a battery transfers to electrical energy which transfers to sound energy in your personal stereo. In the case of the ball falling, gravitational potential energy transfers to kinetic energy, the energy of motion Supercharged Science Page 32

33 POTENTIAL ENERGY Think of potential energy as the could energy. The battery could power the flashlight. The light could turn on. I could make a sound. That ball could fall off the wall. That candy bar could give me energy. Potential energy is the energy that something has that can be released. Objects can store energy as a result of their position Supercharged Science Page 33

34 ELASTIC ENERGY A simple way to demonstrate elastic energy is to stretch a rubber band without releasing it. The stretch in the rubber band is your potential energy. When you let go of the rubber band, you are releasing the potential energy, and when you aim it toward a wall, it s converted into motion (kinetic energy) Supercharged Science Page 34

35 ENERGY TRANSFORMS The rubber band can also show how every is converted from one form to another. If you place the rubber band against a part of you that is sensitive to temperature changes (like a cheek or upper lip), you can sense when the band heats up. Simply stretch and release the rubber band over and over, testing the temperature as you go. Does it feel warmer in certain spots, or in just one location? There are other ways to store potential energy. For example, the battery has the potential energy to light the bulb of the flashlight if the flashlight is turned on and the energy is released from the battery. Your legs have the potential energy to make you hop up and down if you want to release that energy (like you do whenever it s time to do science!). The fuel in a gas tank has the potential energy to make the car move. Those are all ways to store potential energy Supercharged Science Page 35

36 WACKAPOW! Are you ready to drop objects and make a mess? Here s a fun experiment where you can calculate the potential energy and kinetic energy of a system using flour and golf balls 2017 Supercharged Science Page 36

37 POWER We didn t finish with our three concepts of energy, work, and power yet! The important concept of Power is work done over time, and is measured in watts (W), which is a Joule per second (J/s). Work doesn t have anything to do with time, but power does. Sometimes work is done slow, and other times faster. Someone hiking a mountain can reach the peak way before a rock climber, even though they are both traveling the same vertical distance. A hiker in our example has a higher power rating than a rock climber. Power is the rate that work is done Supercharged Science Page 37

38 Measuring Power Overview: Today you ll measure power and have some handy tools to be able to record and interpret data. We use the same materials as last lesson, but introduce an important concept: that of power. Power is work done over time and is measured in watts, which is a Joule per second. What to Learn: You ll be able to have hands-on experience and understand a working definition of energy, work, and power. Materials Meter or yard stick A stopwatch or timer Object Lab Time 1. Grab your 100-gram object and put it on a table. 2. Now lift it off the table straight up until you lift it one meter (one yard). 3. Start the timer and at the same time start lifting the object up and down 20 times. 4. Stop the timer when you re done with the 20 lifts. 5. So, do you have the power of the Dodge Viper? Hmmm, probably not, but let s take a look. 6. First of all, figure out how much work you did. Work = force x distance, so take the force you used and multiply that by the distance you moved it. In this case, you can multiply 1 Newton x 20 meters and get 20 Joules of work. 7. Now figure out how much power you used. Power is work divided by time so take your work (20 Joules) and divide it by how much time it took you to do that work. For example, if you lifted the block 20 times (doing 20 Joules of work) in 5 seconds, you did 20 Joules/5 seconds = 4 Watts of power. To convert Watts to horsepower we multiply by.001 so in this example, you did 4 x.001 =.004 horsepower. 8. Show your calculations in the worksheet below Supercharged Science Page 38

39 Measuring Power Calculations 1. How much work did you do? Show your work. (No pun intended!) 2. How much power did you use? Show your work Supercharged Science Page 39

40 Exercises Answer the questions below: 1. What is work? a. Force divided by distance b. Force times distance c. Energy required for power d. Kinetic and potential energy 2. What is power? a. Work divided by time b. Work multiplied by time c. Energy used in an exercise d. Calories over time 3. How do we measure work? Name one unit. 4. How do we measure power? Name one unit Supercharged Science Page 40

41 Answers to Exercises: Measuring Power 1. What is work? (force times distance) 2. What is power? (work over time) 3. How do we measure work? Name one unit. (Joule, calorie) 4. How do we measure power? Name one unit. (Watt, horsepower) 2017 Supercharged Science Page 41

42 POWER IS SCALAR Is power a vector or a scalar quantity? Power is a scalar, but it s made up of two vector quantities of force and velocity like this: 2017 Supercharged Science Page 42

43 WHAT SIZE ENGINE DO YOU NEED? What if you re wanting to get a motor for a winch on the front of your jeep? What size motor do you need? Here s how to calculate the minimum power so you don t spend more cash than you need to for a motor that will still do the job. (Near the end of the video below, I ll show you how to convert watts to horsepower.) I love to water ski (no kidding!). Here s a neat problem about how to determine some things about the boat and deal with weird units like knots in your calculations Supercharged Science Page 43

44 WORK-ENERGY RELATIONSHIP We ve already studied the different types of forces and learned how to draw free body diagrams. We re going to use those concepts to put forces into two different categories: internal and external forces. Internal forces include forces due to gravity, magnetism, electricity, and springs. External forces include applied, normal, tension, friction, drag and air resistance forces Supercharged Science Page 44

45 MECHANICAL ENERGY RELATIONSHIP The reason why we put the forces into two different categories will be obvious when we start solving physics problems, but for now, you can think of it like this: when total amount of work is done on an object is done by only internal forces, energy will change forms (like going from kinetic to potential energy), and the total amount of mechanical energy is conserved, and the forces are also conserved. When the total amount of work done is done by an external force, the forces are not conserved and the object with either gain or lose energy. As Phillip holds the ball at the top of the building, the ball has 100 Joules of potential energy (the number is just an example). When he drops it, the potential energy of the ball drops since the height of the ball gets less and less. At the same time, however, kinetic energy increases because the speed of the ball increases. All the way down, the sum of the two energies equals 100. No energy gets lost, it only gets transferred. Energy is conserved. Now here s a question you may be asking yourself, If energy is neither created or destroyed in a closed system then why doesn t a pendulum swing forever? That s a very good question. Energy is neither created or destroyed, but it can be transferred into non- useful energy. In the case of a pendulum, every swing loses a little bit of energy,which is why each swing goes slightly less high (achieves slightly less PE) than the swing before it. Where does that energy go? To heat. The second law of thermodynamics states basically that eventually all energy ends up as heat. If you could measure it, you d find that the string, and the weight have a slightly higher temperature then they did when they started due to friction. The energy of your pendulum is lost to heat! If you could prevent the loss of energy to useless energy, you could create a perpetual motion machine. A machine that works forever! There have been a lot of folks who have spent a lot of time trying to make a perpetual motion machine. So far, they have all failed. A perpetual motion machine is one that is said to be 100% energy efficient. In other words all the energy that goes into it goes to useful energy. Your pendulum could be said to be about 90% efficient. Very little energy is converted into useless energy. In most systems, energy is converted to useless heat and sound energy Supercharged Science Page 45

46 ENERGY EXCHANGE BETWEEN KINETIC AND POTENTIAL ENERGY This is an experiment that focuses on the energy transfer of rolling cars. You ll be placing objects and moving them about to gather information about the potential and kinetic energy. All you need are a couple of cars, a ruler, and a propped up table or a plank to roll them down. As you lifted the car onto the track in today s lab, you gave the car potential energy. As the car went down the track and reached the floor, it lost potential energy and gained kinetic energy. When the car hit the floor it no longer had any potential energy, only kinetic. If the car was 100% energy efficient, the car would keep going forever. It would never have any energy transferred to useless energy. Your cars didn t go forever, did they? Nope, they stopped and some stopped before others. The ones that went farther were more energy efficient. Less of their energy was transferred to useless energy than the cars that went less far. Where did the energy go? It went to heat energy, created by the friction of the wheels, and to sound energy. Was energy lost? No, it was only changed. If you could capture the heat energy and the sound energy and add it to the kinetic energy, the sum would be equal to the original amount of energy the car had when it was sitting on top of the ramp Supercharged Science Page 46

47 Go Go Go! Overview: This experiment focuses on the energy transfer of rolling cars. You ll be placing objects and moving them about to gather information about the potential and kinetic energy. What to Learn: This will help us get in touch with the fundamentals of energy transfer, specifically how kinetic and potential energy are related to one another. Materials a few toy cars (or anything that rolls like a skate) a board, book or car track measuring tape Lab Time 1. Set up the track (board or book so that there s a nice slant to the floor). 2. Put a car on the track. 3. Let the car go. 4. Mark or measure how far it went. 5. Experiment with different track configurations. Does this make a difference? Record your results on the data worksheet below. Go Go Go! Data Table Configuration: Description: Distance Traveled: Supercharged Science Page 47

48 Reading As you lifted the car onto the track in today s lab, you gave the car potential energy. As the car went down the track and reached the floor, it lost potential energy and gained kinetic energy. When the car hit the floor it no longer had any potential energy, only kinetic. If the car was 100% energy efficient, the car would keep going forever. It would never have any energy transferred to useless energy. Your cars didn t go forever, did they? Nope, they stopped and some stopped before others. The ones that went farther were more energy efficient. Less of their energy was transferred to useless energy than the cars that went less far. Where did the energy go? It went to heat energy, created by the friction of the wheels, and to sound energy. Was energy lost? No, it was only changed. If you could capture the heat energy and the sound energy and add it to the kinetic energy, the sum would be equal to the original amount of energy the car had when it was sitting on top of the ramp. Exercises Answer the questions below: 1. Where is the potential energy greatest? 2. Where is the kinetic energy greatest? 3. Where is potential energy lowest? 2017 Supercharged Science Page 48

49 4. Where is kinetic energy lowest? 5. Where is KE increasing, and PE is decreasing? 6. Where is PE increasing and KE decreasing? 2017 Supercharged Science Page 49

50 Answers to Exercises: Go Go Go! 1. Where is the potential energy greatest? (A) 2. Where is the kinetic energy greatest? (C) 3. Where is potential energy lowest? (C) 4. Where is kinetic energy lowest? (A) 5. Where is KE increasing, and PE is decreasing? (B) 6. Where is PE increasing and KE decreasing? (D) 2017 Supercharged Science Page 50

51 INCLINED PLANE That ramp is an inclined plane. Inclined planes are simple machines that have played important roles throughout history. Many of the wonders of the world were built using the aid of ramps and other inclined planes (not to mention handy pulleys and levers) to help laborers host the stones that built the pyramids, Great Wall of China, and other feats of engineering. The Assyrians used these ramps to allow their siege engines to tear down an enemy city s walls, and the Romans copied suit. Screws were used by the Greeks and Romans alike, creating fanciful ways to transfer energy, pump water, and even attack enemy troops. Leonardo da Vinci even used a creative screw shape to devise the earliest design for a helicopter! Where are other not-so-obvious places to find an inclined plane? Jar lids, spiral staircases, light bulbs, and key rings are all examples of inclined planes that wind around themselves. Some inclined planes are used to lower and raise things (like a jack or ramp), but they can also used to hold objects together (like jar lids or light bulb threads). Here s a quick experiment you can do to show yourself how something straight, like a ramp, is really the same as a spiral staircase. This making the force less thing is where simple machines come in. Way back when, folks needed to move stuff. Long before there were cranes and bulldozers. They needed to move heavy stuff, rocks, boulders, logs, boats, etc. These clever folks discovered machines. A machine, in science language, is any device that transmits or modifies energy. In other words, energy is put into the machine and comes out of the machine, but along the way the energy does work, changes direction, changes form or all of the above. Most folks say that there are six simple machines. These are the inclined plane, the wheel and axle, the lever, the pulley, the wedge, and the screw. Every machine with moving parts, from a tape player to a car, from a computer to a freight train, is made up of simple machines. Learn more about simple machines here Supercharged Science Page 51

52 Inclined Plane Overview: Energy allows us to do work. We ve had to come up with ways to allow us to do this more easily with things called simple machines. The inclined plane is one example of a simple machine. We ll learn why this is important. What to Learn: You will learn how simple machines help us to do work, as well as some of the ways that they help us in our everyday life. Materials Sheet of paper Short dowel or cardboard tube from a coat hanger Tape Lab Time 1. Cut a right triangle out of paper so that the two sides of the right angle are 11 and 5 ½ (the hypotenuse the side opposite the right angle will be longer than either of these). 2. Find a short dowel or use a cardboard tube from a coat hanger. Roll the triangular paper around the tube beginning at the short side and roll toward the triangle point, keeping the base even as it rolls. 3. Notice that the inclined plane (hypotenuse) spirals up as a tread as you roll. Remind you of screw threads? Those are inclined planes. 1. How does this help you do work? Observations 2. Draw a picture of the inclined plane (left) and then how it is the same as a screw (right) Supercharged Science Page 52

53 Inclined planes have played important roles throughout history. Many of the wonders of the world were built using the aid of ramps and other inclined planes (not to mention handy pulleys and levers) to help laborers host the stones that built the pyramids, Great Wall of China, and other feats of engineering. The Assyrians used these ramps to allow their siege engines to tear down an enemy city s walls, and the Romans copied suit. Screws were used by the Greeks and Romans alike, creating fanciful ways to transfer energy, pump water, and even attack enemy troops. Leonardo da Vinci even used a creative screw shape to devise the earliest design for a helicopter! Reading Energy is the ability to do work. Simple machines enable us to do work over distance. Work happens when something moves a distance against a force. Although it seems a little hard to comprehend, this is truly one of the most useful concepts in physics. I m willing to bet you spend a lot of your time moving things a distance against a force. Do you ever climb stairs, walk, ride a bicycle, or lift a fork to your mouth to eat? Of course you do. Each one of those things requires you to move something a distance against a force. You re using energy and you re doing work. Work is not that hard it s force that can be difficult. Imagine getting up a 10-step flight of stairs without a set of stairs. Your legs don t have the strength/force for you to jump up, you d have to climb up or find a ladder or a rope. The stairs allow you to, slowly but surely, lift yourself from the bottom to the top. Now imagine you are riding your bike and a friend of yours is running beside you. Who s got the tougher job? Your friend, right? You could go for many miles on your bike but your friend will tire out after only a few miles. The bike is easier (requires less force) to do as much work as the runner has to do. Now here s an important point, you and your friend do about the same amount of work. You also do the same amount of work when you go up the stairs versus climbing up the rope. The work is the same, but the force needed to make it happen is much different. Don t worry if that doesn t make sense now. As we move forward, it will become clearer. This making the force less thing is where simple machines come in. Way back when, folks needed to move stuff. Long before there were cranes and bulldozers. They needed to move heavy stuff, rocks, boulders, logs, boats, etc. These clever folks discovered machines. A machine, in science language, is any device that transmits or modifies energy. In other words, energy is put into the machine and comes out of the machine, but along the way the energy does work, changes direction, changes form or all of the above. We re going to focus on the fact that machines can allow you to use less force to do work. Most folks say that there are six simple machines. These are the inclined plane, the wheel and axle, the lever, the pulley, the wedge, and the screw. Every machine with moving parts, from a tape player to a car, from a computer to a freight train, is made up of simple machines. We are going to spend time with two of the simple machines. By learning how they work you will get a nice 2017 Supercharged Science Page 53