Three laws in dynamics, formulated by Sir Isaac Newton - (a) first law: a body continues in a state of rest or of motion with constant velocity in a straight line unless acted upon by some external force; (b) second law: change in momentum is proportional to the force causing the change and to the time during which it acts, and takes place in the same direction as the force; (c) third law: to every action there is an equal and opposite reaction.

【理】牛顿的三个运动定律：惯性定律(静者恒静，动者恒动)；运动定律(动量的改变和力的大小和作用的时间成正比，且和力的方向相同)；反作用定律(对每一个力而言，都有一个与作用力相等，方向相反的反作用力)。