What Two Forces Are at Work to Cause the Motion of the Roller Coaster?

Gravity

• In physics, gravity is what causes objects to be attracted or pulled towards one another. The amount of attraction depends on the mass of the objects. Because the Earth's mass is much larger than anything on its surface, everything around us is constantly being pulled towards it. On a roller coaster, you feel the effects of gravity the moment you are released from the top of the first lift hill. The coaster lets gravity take over: it pulls your coaster's train back towards the surface.

Energy

• On a roller coaster, you experience two types of energy: potential and kinetic. Potential energy is also known as stored energy. When your coaster train is slowly climbing the first lift hill, it is building up energy. Because energy can only be converted into another form and cannot be destroyed (unless other forces, such as friction, are involved), the moment the train starts down the hill it begins to release that energy. At that point, the potential energy becomes kinetic energy. When your train climbs another hill, the kinetic energy again becomes potential energy and the cycle is repeated until the coaster ride is finished.

Friction

• Although friction does not contribute to the excitement of the roller coaster ride, you wouldn't be able to enjoy a coaster without it. Friction works against motions by moving in the opposite direction. This opposing force causes the moving object to release its potential or kinetic energy. On a coaster, friction is used in the braking system to slow down the train or to bring it to a complete stop by draining off the kinetic energy that would, otherwise, keep it looping through the track indefinitely.

Weightlessness

• Some roller coasters give riders the sense of temporary weightlessness. Our sense of weight is actually our recognition of gravity pulling against our mass. That means if you weigh 120 pounds gravity is exerting 120 g's of force on your body. When you are seated on a roller coaster, the seat and your body are pushing against one another thanks to gravity and this keeps you aware of your weight. However, at some points in the ride the force from the seat is removed, usually because the ride's movement causes you to be lifted out of your seat. Without that force from the seat, you don't feel your own weight and, therefore, experience weightlessness.