7 Coaster designers also take advantage of friction to slow the coaster and bring it to a safe stop when breaks are applied at the end of the ride. Friction is a force that works in the opposite direction of an object that is moving along a surface. Friction can come in many forms, but it always resists motion. The amount of friction depends mainly on the materials involved. The most interesting and significant force that acts on a roller coaster is the force of gravity.
Gravity is the force that pulls all objects in the universe toward one another.
If a body, for example a roller coaster, is standing still, it won't want to move unless some force pushes or pulls it. This resistance of the roller coaster to move is called inertia. The more mass a body has the more inertia it has. If the roller coaster is moving, it will want to keep moving, along the direction of motion, unless something causes it to speed up or slow down. This resistance of the moving roller coaster to changing its velocity is another example of its inertia.