What Forces Are at Work During a Roller Coaster Ride?

Gravitational Force

The force that gravity applies on the rider remains constant throughout the ride regardless of the segment. This force represents the rider's weight, or his mass multiplied by the acceleration of gravity, measured at approximately 9.80 meters per second squared. Despite the apparent feelings of weightlessness and weightiness, the gravitational force on the rider remains unchanged throughout the ride. Those feelings are the result of the other forces.

The second force acting directly on the rider is the normal force. This is the force of the seat pressing against the rider. The direction and magnitude of this force change constantly as the orientation of the car on the track changes with each bend, loop and hill. The change in direction and magnitude during a dip is what gives the feeling of weightlessness, as it is essentially a momentary free fall.

Centripetal force is the net inward force as a result of the normal and gravitational forces during a loop or arc. As the car enters the loop or arc, the net force pushes inward, creating the heavy feeling as the body pushes back against the seat. At the top of the loop, however, the normal force and consequently the centripetal force have smaller magnitudes, creating the feeling of weightlessness.

While the motion in a loop is described as circular motion, the loops in modern roller coasters are not exactly circular. Rather, they are clothoid, or teardrop-shaped. This is because truly circular loops cause extreme normal forces that can -- and did when circular loops were used -- cause whiplash, broken bones and even death. The clothoid loop causes a change in acceleration, decreasing the magnitude of the normal force felt by the rider.