Fundamental Equation Newton's Law

The basic relation between mass, acceleration,
and force is contained in Newton’s second law of motion. As
applied to a particle of mass, F 5 ma, force 5 mass 3 acceleration.
This equation is a vector equation, since the direction of F must be the
direction of a, as well as having F equal in magnitude to ma. An alternative
form of Newton’s second law states that the resultant force is
equal to the time rate of change of momentum, F 5 d(mv)/dt.