Unbalanced forces are forces that are not equal and opposite, and they result in a change in velocity. 5 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. No surface is perfectly smooth.
Surface pressure is another condition that affects friction.
A heavy object has more friction than a lighter one. However some of the energy is changed into friction. Coaster designers know that friction plays a part in the ride. Therefore, they make each successive hill lower so that the coaster will be able to make it over each peak. 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.