Newton's third law: for every action there is an equal and opposite reaction. Here is an example : If object A pushes on B, then object B pushes on A just as hard but in the opposite direction, always. Here is another one : suppose the tires of roller Coaster push against the track while the track pushes back on the tires—the tires and road simultaneously push against each other.Thus the reactive force of track pushes the Coaster ahead.
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