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N

Newton's Third Law of Motion

Whenever a first object exerts a force on a second object, the first object experiences a force equal in magnitude but opposite in direction to the force that it exerts. Forces always occur in pairs.

Normal force

The force a surface exerts on an object, perpendicular to the surface, to support the object's weight. On a horizontal surface, it is equal in magnitude to the object's weight but opposite in direction. (N = mg)