Energy Conservation and Conversion. 8 th Grade Science Adapted from the Prentice Hall Science Explorer: Motion, Forces, and Energy. Introduction to Energy Conversion: Niagara Falls, New York.
8th Grade Science
Adapted from the Prentice Hall Science Explorer: Motion, Forces, and Energy
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.
Photo courtesy of: niagara.ettractions.com
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 alispagnola.blogspot.com
In an electrical motor, electrical energy is converted to mechanical energy that can be used to run a machine.
Your body converts the chemical energy in food you eat to the mechanical energy you need to move your muscles.
Chemical energy in food is also converted to the thermal energy your body uses to maintain its temperature.
Chemical energy is even converted to the electrical energy your brain uses to think.
Photo from homeworkoutpros.com
If you strike a match, the mechanical energy that is used to strike a match is converted to thermal (heat) energy.
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.
Read more about internal and external combustion engines here.
Electrical energy produces a hot spark.
The thermal energy of the spark releases chemical energy in the fuel.
When the fuel burns, this chemical energy in turn becomes thermal energy.
Thermal energy is converted to mechanical energy used to move the car, and finally..
To electrical energy that produces more sparks.
This diagram is an example of energy conversion in a hybrid engine.
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.
When you stretch a rubber band, you give it elastic potential energy.
If you let it go, the rubber band flies across the room.
When the rubber band is moving, it has kinetic energy.
The potential energy of the stretched rubber band is converted to the kinetic energy of the moving rubber band.
Maximum gravitational potential energy Rubber BandEnergy Conversion in Juggling
50% potential energy
50% kinetic energy
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 kinetic energy
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: niagara.ettractions.com
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?
fphoto.photoshelter.com Rubber BandEnergy Conversion in a Pendulum
Maximum potential energy
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 kinetic energy
Here are a few important points to remember:
If use the example of the pendulum from before, if you set that pendulum in motion, will it remain in motion forever?
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.
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.
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.
under normal circumstances;
however it is important to remember that there is one example of when energy can be created by destroying matter.
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 here.
Want more on Einstein’s Theory of Relativity?
Click here and click here to see how nuclear power works.
don’t confuse energy conservation with energy conservation.
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.
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!