three laws of mechanics describing the motion of a body. The first law states that a body remains at rest or in uniform motion in a straight line unless acted upon by a force. The second law states that a body's rate of change of momentum is proportional to the force causing it. The third law states that when a force acts on a body due to another body, then an equal and opposite force acts simultaneously on that body
Newton's laws of motion The three laws proposed by Sir Isaac Newton concerning relations between force, motion, acceleration, mass, and inertia. These laws form the basis of classical mechanics and were elemental in solidifying the concepts of force, mass, and inertia. ◇ Newton's first law states that a body at rest will remain at rest, and a body in motion will remain in motion with a constant velocity, unless acted upon by a force. This law is also called the law of inertia. ◇ Newton's second law states that a force acting on a body is equal to the acceleration of that body times its mass. Expressed mathematically, F = ma, where F is the force in Newtons, m is the mass of the body in kilograms, and a is the acceleration in meters per second per second. ◇ Newton's third law states that for every action there is an equal and opposite reaction. Thus, if one body exerts a force F on a second body, the first body also undergoes a force of the same strength but in the opposite direction. This law lies behind the design of rocket propulsion, in which matter forced out of a burner at high speeds creates an equal force driving the rocket forward.
The three laws that govern the motion of material objects. They were first written down by Isaac Newton in the seventeenth century and gave rise to a general view of nature known as the clockwork universe. The laws are: (1) Every object moves in a straight line unless acted upon by a force. (2) The acceleration of an object is directly proportional to the net force exerted and inversely proportional to the object's mass. (3) For every action, there is an equal and opposite reaction.
Note: Until the beginning of the twentieth century, these three laws, together with the laws of thermodynamics and Maxwell's equations, were thought to explain the entire physical universe.