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Q & A: Momentum is Relative!

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Most recent answer: 07/15/2009
Q:
As I understand it, velocity is relative to the frame of reference. Does that mean that Momentum P (mass * velocity) is relative too?
- Matt Rogers (age 46)
Hollis, NH USA
A:
Yes Matt, you are correct.  Momentum is relative to the frame of reference.  A good example showing this is considering people throwing balls on a moving train.  Let's say the people on the train think that they are throwing the ball at a velocity of 20 meters per second.  Let's also assign some mass of one kilogram to the ball.  Therefore, according to the people on the train, the momentum of the ball is 20 kilogram*meters per second.  If the train is traveling by some people on the ground at, say, 10 meters per second, then the velocities would add and change the momentum.  I.e. to people on the ground, the ball would have a momentum of 30 kilogram*meters per second.

-Mark

(published on 07/15/2009)

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