✔ 最佳答案
Linear momentum is a physical quantity defined as the product of mass and velocity. Because velocity is a vector quantitiy, linear momentum is thus a vector quantity.
Momentum plays an important role in physics. It can be shown that in an isolated system, the total momentum of the system remains constant. This is the Law of Conservation of Momentum.
2010-03-30 20:55:41 補充：
Answer ot your further question:
By default, momentum generally refers to linear momentum (i.e. applies to objects moving in a straight line, hence the word "linear"). For objects with rotational motion, there is an ANGULAR MOMENTUM. The momentum conservation law equally applies to angular momentum.
