Newton's second law relates the net force acting on an object to its mass and the acceleration it feels. Mathematically the net force is equal to the product of the mass and the acceleration. Remember this is the net force, which is the sum of all applied forces. In some cases (like most of the videos presented here) only one or two forces acts on an object. In that case the net force is just that one force, or the vector sum of those two forces. Newton's second law is a natural extension of what we learned about Newton's first law, that objects will move with constant (possibly zero) velocity unless a force acts to change that velocity. Newton's second law tells us how a force changes velocity by way of the relationship between velocity and acceleration.
© 2008 Kansas State University Physics Education Research Group.