laws of motion

GNU Webster's 1913

1. n. (Physics) three laws defined by Sir Isaac Newton: (1) Every body perseveres in its state of rest or of moving uniformly in a straight line, except so far as it is made to change that state by external force. (2) Change of motion is proportional to the impressed force, and takes place in the direction in which the force is impressed. (3) Reaction is always equal and opposite to action, that is to say, the actions of two bodies upon each other are always equal and in opposite directions.