Newton's third law states that for every action, there is an equal and opposite reaction, with forces acting on different objects. Examples include a ball hanging from a string, where the ball pulls down while the string pulls up, and a person pulling the Earth towards them as the Earth pulls back with equal force. Kicking a soccer ball demonstrates this law, as the force exerted on the ball is matched by the force the ball exerts back on the kicker. Pressing a keyboard key also illustrates the principle, as the key pushes back against the finger. Additionally, when walking, the backward force applied to the Earth results in a forward motion due to the reaction force.