A roller coaster is similar to a slide except it is longer and you ride in a train car rather than on the seat of your pants. 4 Force is a push or pull. Balanced forces are equal forces that are applied in opposite directions and result in no change in velocity. 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.