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B. inggris Sekolah Menengah Atas What You Need to Know Roller-coaster engineering is the branch of engineering concerned with designing, constructing, and testing rollercoaster cars and the paths they follow. Since part of the testing means these engineers have to actually ride on the roller coasters, you might think this would be a pretty fun job. In designing roller coasters, engineers try to create a ride that is thrilling and fun but also safe. When moving up hill on a roller-coaster track, the cars are moving against the pull of gravity. So the train of cars must be pulled up the first and generally the tallest hill of the track. At the top of the hill, the cars have potential energy (stored energy). The amount of potential energy of an object that is raised depends on its weight (force of gravity) and the height it is raised. The greater its weight and the higher it is raised, the greater the potential energy. Generally, the potential energy of the roller-coaster cars at the top of the first hill is their source of energy for the rest of the ride. This is because energy (ability to do work) can be changed from one form to another. Kinetic energy is the energy of a moving object. As gravity pulls the cars down the first hill, their potential energy begins to change to kinetic energy. The farther they move, the faster 27

they move and the more kinetic energy they have. They reach their fastest speed at the bottom of the hill. At this point, they have zero potential energy and maximum kinetic energy. The cars continue to move, climbing the second hill using kinetic energy. As they move up the hill, they are again moving against the pull of gravity, which decreases their speed and kinetic energy. However, their potential energy increases again as their height increases. At the top of the second hill, the cars have zero kinetic energy and maximum potential energy. But the amount of potential energy is less than the original amount. This is because some of the original potential energy was changed into other forms of energy such as heat and sound that do not cause the cars to move. As the total potential energy decreases, the total kinetic energy also decreases. As the kinetic energy decreases, the hills must be shorter. Some roller coasters include loops. Roller-coaster engineers have to design the loops so that the cars can stay on the track even when they are upside down. For the cars to move in a circular path, there must be a constant force pushing them toward the center of the curved path. This center-seeking force is called centripetal force. This action force is balanced by a center-fleeing reaction force called centrifugal force. While centripetal force is a real force acting on the moving cars, centrifugal force is an apparent force due to inertia. Inertiais the tendency of an object at rest to remain at rest and for an object in motion to continue in motion. If an object is going in a straight line, it tends to keep going in a straight line. This is what happens to a roller-coaster car. As the car goes up into the loop, the car keeps going in a straight line but the track pushes it toward the center of the loop. Inertia creates what seems like a force pushing the car outward from the cen

28 Engineering for Every Kid ter of the looped track. It is not a real force, instead, it is inertia trying to make the car go in a straight line. The faster the car moves, the greater its centripetal and centrifugal forces. The speed necessary to hold the car on the track depends on the shape of the loop. Roller-coaster engineers want a loop that makes the ride exciting, but it also has to be safe. If the loop were a perfect circle, the speed needed to keep the car on the track would create a force that would be harmful to the people riding the roller coaster.​

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