p = (mass) * (velocity)It is a vector quantity, and the total linear momentum of a bunch of objects will remain the same, before and after a collision.
impulse = (force) * (time)if the force has a constant magnitude during its action. If the force changes with time, then one must integrate to find the impulse:
/ impulse = | (force) dt /
(change in momentum) = (impulse) p - p = (force) * (time) final initial m*v - m*v = (force) * (time) final initial