Momentum reflects the tendency of a object to continue in the direction of its current velocity. To derive momentum and impulse, begin with Newton's Second Law
ma = m dv/dt
and then integrate with respect to time,
This equation may be easier to deal with if it is re-written as
If this equation is analyzed using rectangular coordinates, it can be expressed as three scalar equations,
These equations state that the impulse applied to an object equals its change in linear momentum. If the external forces acting on an object are known as a function of time, the change in velocity can be determined.