Explain why there is an equal and opposite reaction to every action?

Newton described the relationship between forces acting on a body and its motion in response to these forces in his three laws of motion. His third law describes what happens when two bodies each exert force on the other. When these forces are exerted, they are equal in magnitude but opposite in direction. For example, a person walks and pushes against the floor and the floor, pushes against the person. This is also referred to as the action-reaction law. Whenever a first body exerts a force F on a second body, the second body exerts an opposite force -F on the first body. If two people collide into eachother, each is exerting a force on the other.
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