If Object 1 exerts a force F1 on Object 2, then Object 2 exerts a force F2 on Object 1. These forces have the same magnitude but act in opposite directions (F1 = -F2) and act on different objects. These two forces form an action-reaction pair. For every action, there is an equal but opposite reaction. However, the effects of these equal-strength forces can be different. For example, imagine a collision between a bus and a pedestrian. Both the bus and the pedestrian experience equal force, but the pedestrian has less mass and so will undergo more acceleration. The bus will undergo very little acceleration.