Air Resistance is the force that opposes the motion of objects through air. The amount of air resistance acting on an object depends on the size, shape, and speed of the object. Air resistance affects a flat sheet of paper more then a crumpled one. Acceleration stops at the Terminal velocity. The upward force of air resistance continues to increase until it is equal to the downward force of gravity. The net force is 0 N and the object stops accelerating. Free Fall occurs when there is no air resistance. Skydivers are often described as being in free fall before they open their parachutes. However, air resistance is always acting on the skydiver not the parachute. Because air resistance is a force, free fall can occur only where there is no air.