Newton’s three laws of motion ...
(quoted from Robert Resnick and David Halliday, Physics for Students of Science and Engineering, Part I (New York: John Wiley & Sons, 1962)
Every body persists in its state of rest or of uniform motion in a straight line unless it is compelled to change that state by forces acted upon it.
The acceleration caused by one or many forces acting on a body is proportional in magnitude to the resultant of the forces, and parallel to it in direction, and is inversely proportional to the mass of the body.
To every action there is always opposed an equal reaction.
