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#The rate of change of an object's [[momentum]] is equal to the net force acting on it (<math> \vec F = d{\vec p}/dt </math>, sometimes written as <math> \vec F = m\ \vec a</math> when mass can be assumed to be constant).

#For every action there is an equal and opposite reaction; or, more precisely, the total momentum of any isolated system is always constant.

==Explanation==