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Getting to Know: Kinetic Energy The motion of a rollercoaster thrills riders as they fly down hills, twist around corners, and even wind up topsy-turvy as they pass through loops of track. You may have noticed that rollercoaster cars are pulled up the first hill by a motor and chain, but once they reach the top, the cars roll through the remainder of the ride without any help from outside forces. It’s easy to imagine that gravity pulls the cars down the hill, but how do they get up the next hill or through the loops? The answer is in the energy of the cars as they roll through the ride. What is energy? People use the words “energy” and “work” in a lot of different ways, but in science, energy is the ability to do work and work is moving a mass over a distance. Energy comes in many forms and can change from one form to another. Kinetic energy is the energy that a moving object has as a result of its mass and its motion. The kinetic energy of an object is equal to one-half of its mass times the square of its velocity. Velocity is a measurement that accounts for both speed and direction. The A rollercoaster works because energy rollercoaster cars have kinetic energy as they move continually changes form between potential and kinetic energy. along the track. The cars also have potential energy, which is stored energy that can be released to do work. Potential energy increases with height above Earth’s surface because the force of gravity will move an object downward once the object is released from its position. During the ride, the energy of the rollercoaster cars continually changes between potential and kinetic. Misconception 1: Isn’t energy the same thing as force? No, energy and force are two different things. A force is a push or a pull. For example, a chain exerts force on the rollercoaster cars when it pulls them up to the top of the first hill. The force of gravity pulls the rollercoaster cars down the tracks. However, the rollercoaster cars have energy—the ability to do work. In this case, the work is moving the mass of the cars and the riders over the distance of the track. Concept: Kinetic Energy Getting to Know www.discoveryeducation.com 1 © Discovery Education. All rights reserved. Discovery Education is a subsidiary of Discovery Communications, LLC. How does energy change forms? On the rollercoaster ride, energy changes forms between potential and kinetic every time the cars move up or down. At the top of the first hill, the cars have a lot of potential energy. As the cars move down the hill, some of that potential energy changes to kinetic energy. A car’s kinetic energy carries it up the next hill, and kinetic energy changes to potential energy as the car moves upward. As a car crests the hill and starts moving downward again, some of its potential energy changes back to kinetic energy. These changes continue throughout the ride. Misconception 2: Some energy is destroyed as it changes from one form to another. That’s why the rollercoaster slows on each hill and eventually comes to a stop. Actually, energy can never be created or destroyed; it can only change form. The rollercoaster cars slow as they lose kinetic energy, but that kinetic energy isn’t destroyed; it simply changes to another form of energy. The rollercoaster slows as some of its kinetic energy changes to heat energy as a result of friction. Friction is the force caused by objects rubbing together. Friction causes objects that rub together to heat up. Can kinetic energy transfer from one object to another? It can! Remember that energy is the ability to do work or to move a mass over a distance. When one moving object comes into contact with another object, it applies a force that can move that object. When the second object moves, it gains kinetic energy from the first object—energy transfer has occurred. Think about hitting a ball with a bat. The swinging bat has kinetic energy. When the bat hits the ball, it applies force that moves the ball in the direction of the swing. Some of the bat’s kinetic energy has transferred to the ball. Now that you know a little more about kinetic energy, let’s get started with our lesson! When the batter hits the ball, the kinetic energy of the swinging bat transfers to the ball and the ball flies through the air. Concept: Kinetic Energy Getting to Know www.discoveryeducation.com 2 © Discovery Education. All rights reserved. Discovery Education is a subsidiary of Discovery Communications, LLC.