Newton’s law of motion
First law: Everybody continues in its state to rest or of uniform motion in a straight line except in so far as it is compelled by an external force to change that state.
Second law: The rate of change of momentum of a body is directly to proportion to its force and change of momentum takes place along the direction of the force.
Third law: To every action the is an equal and opposite reaction.
∴ F = – F