Things only move when they are forced to move! A bicycle only moves when a force is applied in the form of pedaling. A cloud on the sky only moves when a force is applied in the form of a storm or a wind. A soccer ball only flies into the goal net when a force in the form of a beautiful and precise shot from Peter Møller or another great soccer player is applied. Thus all sorts of transport only take place when a force, called a driving force, is applied. This is also the case when we are talking about transport of other things than bicycles, clouds and soccer balls.