A rollercoaster is an amusement park ride that consists of a light railroad track with many tight turns and steep slopes, where people ride in small, fast, open cars.

There are several components that make rollercoasters work safely.

The chain lift pulls the car up hills.

The catapult launcher lift is another way of moving the car, using energy and compressed air. 

The brake is a safety mechanism that can slow down or stop the ride for the safety of the riders.

Gravitational potential energy is greatest at the highest point of the rollercoaster and least at the lowest point.

Potential energy is the energy of a particle, body, or system that is determined by its position or structure.

Gravity is the force by which all objects in the universe are attracted to each other.

The maximum kinetic energy is at the point when the car passes through the bottom of a loop.

Kinetic energy is energy resulting from motion.

Each loop is slightly lower than the previous one because the car loses energy as it goes.

Force from a circular path provided by the track pushing against the car allows it to "loop the loop".

The car has less energy at the end of the ride than at the start due to friction and air resistance.

Ultimately, rollercoasters are build very carefully to ensure safety.

Gravity and friction are used to make the rollercoaster work.