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| Fig. 5-1 The roller coaster in the Ocean Park | |||
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Roller coaster I |
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Roller coaster II |
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Have you ever ridden the roller coaster in the Ocean Park? Taking sharp turns and high loops would certainly give you an exciting and thrilling experience. You may think that a motor is required to keep the roller coaster in going through turns and loops. However, this is not the case. After the roller coaster has been pulled by the machinery to the first hill of maximum height, it is released and let to fall and rise on its own. So what keeps it moving? The secret lies in the inter-conversion of potential energy and kinetic energy.
Let's explain the motion of the roller coaster by the energy consideration. When the cart runs down from the maximum height, its potential energy is being converted into kinetic energy. As a result, the cart moves faster and faster as it descends. If ideally no energy is lost by friction, the lost in potential energy will be exactly equal to the gain in kinetic energy, as according to the principle of conservation of energy. When the cart goes up another hill, kinetic energy is converted back to potential energy and so the cart loses speed. In the rises and falls, the potential energy and kinetic energy interchange continuously, but the total energy of the cart, i.e., the sum of potential energy and kinetic energy, remains unchanged.
In reality, however, friction always exists between the cart and the rail, so that energy is lost continuously as heat as the cart travels. That is why the first hill must be the highest one, otherwise the cart would not have enough energy to go through the following hills and loops.
Flash
animation: Motion of a roller coaster
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