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12.2: Energy Conservation

Difficulty Level: Basic Created by: CK-12
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What can a roller coaster tell us about energy?

This string of cars is about to change energy from potential to kinetic. The energy is not lost; it just changes forms. The cars are pulled to the top of the first hill. The rest of the ride runs on the potential energy the cars had at that time.

Conservation of Energy

In this section, we're not talking about saving energy. This section is about how energy cannot be created or destroyed. Energy can only change forms. So we say that energy is conserved. Energy changes form when something happens. But the total amount of energy always stays the same. The Law of Conservation of Energy says that energy cannot be created or destroyed. Scientists observed that energy could change from one form to another. They also observed that the overall amount of energy did not change.

Energy Changes

Here is an example of how energy changes form: kicking a soccer ball. Your body gets energy from food. Where does the food get its energy? If you're eating a plant, then the energy comes directly from the sun. If you're eating an animal, then the energy comes from a plant that got its energy from the sun.

Your body breaks down the food. It converts the food to chemical energy and stores it. When you are about to kick the ball, the energy must be changed again. Potential energy has the potential to do work. When your leg is poised to kick the ball but is not yet moving, your leg has potential energy. A ball at the top of a hill has the potential energy of location.

Kinetic energy is the energy of anything in motion. Your muscles move your leg, your foot kicks the ball, and the ball gains kinetic energy ( Figure below ). The kinetic energy was converted from potential energy that was in your leg before the kick. The action of kicking the ball is energy changing forms. The same is true for anything that involves change.

Kicking a soccer ball takes energy from your food and gives it to the soccer ball.

Vocabulary

• chemical energy : Energy that is stored in the chemical bonds in molecules.
• kinetic energy : The energy that an object in motion has because of its motion.
• potential energy : Energy stored within a physical system that has the potential to do work.

Summary

• Energy cannot be created or destroyed. This is the Law of Conservation of Energy.
• Energy changes from one form to another.
• Some types of energy are chemical, kinetic and potential.

Practice

Use this resource to answer the questions that follow.

How Energy Changes at http://www.youtube.com/watch?v=A7Mab_NHXRE (1:51)

1. What types of energy is released when a light bulb is turned on?
2. What type of energy turns on the light bulb?
3. List the types of energy involved in a baseball being hit by a bat.
4. List the types of energy involved in releasing an arrow from a bow.
5. List the types of energy involved in making electricity.

Review

1. Compare and contrast potential energy and kinetic energy.
2. What does it mean to say that energy cannot be created or destroyed.
3. Think about riding a bike up and down a hill. Where does energy change form in each step of the process?

Basic

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Jan 04, 2013

Aug 25, 2014