Newton's Second Law of Motion

Newton's Second Law The relationship between an object's mass m, its acceleration a, and the applied force F is F = ma. Acceleration and force are vectors; in this law the direction of the force vector is the same as the direction of the acceleration vector.

This is the most powerful of Newton's three laws, because it allows quantitative calculations of dynamics (how do velocities change when forces are applied). Notice the fundamental difference between Newton's second law and the dynamics of Aristotle: according to Newton, a force causes only a change in velocity (an acceleration); it does not maintain the velocity as Aristotle held.

This is sometimes summarized by saying that according to Newton, F = ma, but according to Aristotle F = mv, where v is the velocity. Thus, according to Aristotle there is only a velocity if there is a force, but according to Newton an object with a certain velocity maintains that velocity unless a force acts on it to cause an acceleration (that is, a change in the velocity). So remember, F = ma (it's the law!).

Animation: Newton's second law