Answer:
A roller coaster uses physics by applying simple mechanical principles. This amusement ride is a gravity operated, fixed course, recreational vehicle. Let's see how it works.
A string of cars on a closed track is filled with riders. Those cars and riders have some amount of mass. The cars are engaged to a mechanism that pulls them up to a high point on the track, and this adds potential energy to the cars and riders. The cars are then released over top of that high point, and gravity pulls them down accelerating them. The cars gather speed, and their inertia carries them through some ups and downs and loops and corkscrews (or whatever else the ride is designed to do), and all of this with the energy that was put in by the lifting mechanism.
There are frictional losses throughout the ride, but the mass of the cars and riders is calculated so that there is plenty of energy added at the start to allow the car string and its riders to reach the end of the ride. There, the remaining energy is bled off using a braking system, and the cars are brought to a safe stop so the riders may disembark.