mo·men·tum /moˈmɛntəm, mə-/
  動力,要素
  mo·men·tum /moˈmɛntəm, məˈmɛnt-/ 名詞
  momentum
  動量
  Mo·men·tum n.; pl. L. Momenta F. Momentums
  1. Mech. The quantity of motion in a moving body, being always proportioned to the quantity of matter multiplied by the velocity; impetus.
  2. Essential element, or constituent element.
     I shall state the several momenta of the distinction in separate propositions.   --Sir W. Hamilton.
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  momentum
       n 1: an impelling force or strength; "the car's momentum carried
            it off the road" [syn: impulse]
       2: the product of a body's mass and its velocity; "the momentum
          of the particles was deduced from meteoritic velocities"
       [also: momenta (pl)]