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Energy Conservation and Conversion 8 th Grade Science Adapted from the Prentice Hall Science Explorer: Motion, Forces, and Energy.

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Presentation on theme: "Energy Conservation and Conversion 8 th Grade Science Adapted from the Prentice Hall Science Explorer: Motion, Forces, and Energy."— Presentation transcript:


2 Energy Conservation and Conversion 8 th Grade Science Adapted from the Prentice Hall Science Explorer: Motion, Forces, and Energy

3 Introduction to Energy Conversion: Niagara Falls, New York Niagara Falls is a spectacular natural phenomenon that attracts millions of tourists every year. It is located partially in New York state and partially in Canada. In addition to being a beautiful and spectacular sight to see, Niagara Falls is also the center of a network of electrical power lines. Water that is diverted above the falls is used to generate electricity for much of the neighboring region. Niagara Falls is a perfect example of how energy can be converted from potential energy to kinetic energy (electricity). Watch this link for more information about energy conversion and Niagara Falls. aQM Photo courtesy of:

4 So, what is energy conversion? In the example at Niagara Falls, moving water is converted, or transformed, into electrical energy. A change from one form of energy to another is called an energy conversion. It is important to remember that most forms of energy can be converted into other forms. The picture here is of a toaster. A toaster is an example of how electrical energy is converted to thermal energy. In other words, the toaster uses electrical energy to produce heat energy. Artwork courtesy of

5 What are some other examples of energy conversion? 1. In an electrical motor, electrical energy is converted to mechanical energy that can be used to run a machine. 2. Your body converts the chemical energy in food you eat to the mechanical energy you need to move your muscles. 3. Chemical energy in food is also converted to the thermal energy your body uses to maintain its temperature. 4. Chemical energy is even converted to the electrical energy your brain uses to think. Photo from

6 Often a series of energy conversions is needed to do a task. For example… 1. If you strike a match, the mechanical energy that is used to strike a match is converted to thermal (heat) energy. 2. The thermal energy causes the match to release stored chemical energy, which is converted to thermal energy and to the energy you see as light.

7 A car engine is another example of how a series of conversions occur. 1. Electrical energy produces a hot spark. 2. The thermal energy of the spark releases chemical energy in the fuel. 3. When the fuel burns, this chemical energy in turn becomes thermal energy. 4. Thermal energy is converted to mechanical energy used to move the car, and finally.. 5. To electrical energy that produces more sparks. Read more about internal and external combustion engines This diagram is an example of energy conversion in a hybrid engine.

8 Energy Conversions Between Potential and Kinetic Energy O For instance, in the example with the match… there is potential energy in the match and when it is struck it becomes kinetic energy. O The next slides are examples of conversions between just potential and kinetic energy…but, remember all of these examples also involve conversions between types of energy too (electrical, mechanical, chemical, etc.) The previous examples show conversions between specific kinds of energy. Keep in the mind, though, that all energy conversions are also conversions between potential and kinetic energy.

9 Energy Conversions Between Potential and Kinetic Energy: The Rubber Band 1. When you stretch a rubber band, you give it elastic potential energy. 2. If you let it go, the rubber band flies across the room. 3. When the rubber band is moving, it has kinetic energy. 4. The potential energy of the stretched rubber band is converted to the kinetic energy of the moving rubber band.

10 Energy Conversion in Juggling So, maybe we aren’t all jugglers, but it is a great example of kinetic and gravitational potential energy. When the ball moves, it has kinetic energy, when it rises, it slows down, so the kinetic energy decreases. When the ball is at its highest point, it stops moving for a fraction of a second where it has potential energy. This then converts to kinetic energy. The kinetic energy increases while the potential energy decreases. Who knew there was so much potential and kinetic energy at the circus? Maximum gravitational potential energy 50% potential energy 50% kinetic energy Maximum kinetic energy

11 Energy Conversion in a Waterfall Okay, let’s go back to Niagara Falls for a minute. There is conversion between potential and kinetic energy on a large scale at Niagara Falls. The water at the top of the falls has gravitational potential energy because it is higher than the bottom of the falls. But as the water falls, its height decreases and so it loses potential energy. At the same time, its kinetic energy increases. Photo courtesy of:

12 Energy Conversion in a Pole Vault Pole vaulting is a track and field event. As a pole vaulter runs, he has kinetic energy because he is moving. When he plants his pole to jump, the pole bends. His kinetic energy is converted to elastic potential energy in the pole. As the pole straightens out, the vaulter is lifted high into the air. The elastic potential energy of the pole is converted to the gravitational potential energy of the pole vaulter. Once over the bar, the vaulter’s gravitational potential energy is converted into kinetic energy as he falls to the safety cushion below. Whew! Got that?

13 Energy Conversion in a Pendulum You can find pendulums in a clock, but the motion of a pendulum can be found anytime you swing an object back and forth (like a tetherball or even swinging your shoes from your shoelaces). A continuous conversion between kinetic energy and potential energy takes place in a pendulum. At the highest point in its swing, the pendulum has only gravitational potential energy. As the pendulum starts to swing downward, it speeds up and its gravitational potential energy changes to kinetic energy. At the bottom of its swing, all its energy is kinetic energy. Then, as it swings, to the other side, and slows down, it regains gravitational potential energy, and at the same time loses kinetic energy. At the top of its swing on the other side it again has only gravitational potential energy. And so the pattern of energy conversion continues. Maximum potential energy Maximum kinetic energy

14 Do you feel you understand energy conversion now? O Energy conversion can also be called energy transformation. When you think of transformation, you think of change, so… O Energy conversion is a change from one form of energy to another. O Most forms of energy can be converted into other forms. O The most common conversions of energy happen between potential energy and kinetic energy. Here are a few important points to remember:

15 So, what is energy conservation? If use the example of the pendulum from before, if you set that pendulum in motion, will it remain in motion forever?

16 No, the pendulum will not stay in motion forever. O According to the Law of Conservation of Energy, energy cannot be created or destroyed. O The total amount of energy is the same before and after any process. O All energy can be accounted for. Does that mean that the energy is destroyed over time? The answer is no. The law of conservation of energy states that when one form of energy is converted to another, no energy is destroyed in the process.

17 Energy and Friction O The energy is not destroyed, it simply changes form. So, what happens to the kinetic energy of the pendulum? As the pendulum moves, it encounters friction at the pivot of the string and from the air through which it moves. When an object experiences friction, the motion (thus, kinetic energy) decreases. This means its thermal energy increases. So the mechanical energy of the moving pendulum is converted to thermal energy. The pendulum slows down, but the energy is not destroyed.

18 Energy and Friction continued… In the pendulum example, friction converted mechanical energy to thermal energy. Another example of this is when you rub your hands together to warm them up. The mechanical energy of rubbing your hands together is converted to thermal (heat) energy.

19 Energy and matter cannot be created or destroyed… under normal circumstances; however it is important to remember that there is one example of when energy can be created by destroying matter.

20 The Theory of Relativity Maybe you’ve heard of this man? Albert Einstein explained that energy can sometimes be created– by destroying matter! This process is not important for most of the energy conversions we have talked about, but it is very important in nuclear reactions, where huge amounts of energy are produced by destroying tiny amounts of matter. This discovery means that in some situations energy alone is not conserved. Just as different forms of energy can be converted from one form to another, matter can sometimes be converted to energy. Want more on Einstein? Click here, or Want more on Einstein’s Theory of Relativity? Click here and click here to see how nuclear power

21 And, on a last note… O Energy conservation can mean what we’ve been talking about– energy cannot be created or destroyed (under normal circumstances), but can be converted. O At the same time, energy conservation can mean saving energy by turning off lights, using less gas, etc. But, that is another discussion for another date in time! (soon!) don’t confuse energy conservation with energy conservation. What?

22 Follow Up Assignment O You will also have a quiz at a later date on this information. O Please go to the next slide to get information about this! In order to assess your understanding of energy conversion, you will complete an activity that asks you to analyze the energy conversions that are taking place in different activities. Please refer to your Science Homepage for more details.

23 Are you ready to be quizzed? O What is energy conversion? O How is eating something an example of energy conversion? O What does it mean when I say “often a series of energy conversions is needed to complete a task”? O What is the most common type of energy conversions? O Be able to explain the energy conversions that take place in 2 of the following: car engine, juggling, waterfalls, pole vaulting, or pendulums. O What does the law of conservation of energy state? The following information will be on a quiz. Use the questions on this page to quiz yourself before you take the real thing. If you need to go back and review something, please do so because once you have the quiz you will not be allowed to go back to this PowerPoint!

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