# Potential and Kinetic Energy

Potential energy is energy that is stored in an object. If you stretch a rubber band, you will give it potential energy. The more you stretch the rubber band, the more potential energy it gains. As the rubber band is released, potential energy is changed to motion.

Kinetic energy is energy of motion. A rubber band flying through the air has kinetic energy. When you are walking or running, your body is exhibiting kinetic energy. Typically, potential energy is converted into kinetic energy and vice versa.

Before the yo-yo begins its fall, it has stored energy due to its position. At the top, the yo-yo has its maximum potential energy. As it starts to fall, the potential energy begins to be changed into kinetic energy. At the bottom, its potential energy has been converted into kinetic energy so that it now has its maximum kinetic energy. As the yo-yo returns to your hand, it converts the kinetic energy back into potential energy.

A waterfall, like in the QuickTime video above, has both potential and kinetic energy. In the movie above, water at the top of Bridal Veil Falls has stored potential energy. When the water begins to fall, its potential energy is changed into kinetic energy. This change in energy also happens at Niagara Falls where it is used to provide electricity to parts of the Northeastern United States through the transformation of mechanical energy into and electromagnetic energy.
 Amusement parks use the concept of converting between potential and kinetic energy. An example of this is the freefall ride shown at the left. Notice that kinetic energy is used to bring the ride to the top. Once the car is at the top, it pauses - held by the ride. When the ride releases the car, it rushes downward much like the yo-yo mentioned earlier. Notice, the potential energy at the top is now transformed into kinetic energy as the car falls. Many other amusement park rides include this same concept. Imagine going to your favorite amusement park and riding the rides. Can you remember any rides where the thrill was based on converting potential energy into kinetic energy and back again?

Analysis:

1. What ride is your favorite at an amusement park?
• Where on this ride is the maximum potential energy?
• Where on the ride is the minimum kinetic energy?
• Where on the ride did you feel a conversion between potential and kinetic energy?
2. What ride was your least favorite?
• How is your opinion of this ride related to converting between potential and kinetic energy?

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