Which law states that force equals mass times acceleration?

The law stating that force equals mass times acceleration is Newton’s second law of motion. In its familiar form, F = ma, it says that an object’s acceleration depends on the net force acting on it and its mass.

Newton published his three laws of motion in Philosophiæ Naturalis Principia Mathematica in 1687. The modern F = ma formula is a special case of the more general second-law expression F = dp/dt, where force equals the rate of change of momentum. When mass remains constant, momentum is mass multiplied by velocity, giving F = ma.

The word “force” here means net force: all pushes and pulls must be combined as vectors, including their directions. If the net force is zero, acceleration is zero, so an object remains at rest or continues moving at constant velocity. This law is often confused with the first law, which describes inertia, or the law of gravitation, which describes one particular force rather than the general relationship between force, mass and acceleration.