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I've $3F.r + 2F.2r - F . r = 6Fr$ momentum. is this momentum at clockwise or counter clockwise? And why? sorry for these questions because I'm new at here. Thanks!

  • what do you mean? –  May 03 '17 at 13:13
  • this is solution of a momentum question. But couldn't find clock wise or counter clockwise. –  May 03 '17 at 13:18
  • I just wonder is it clock wise or counter clock wise? and why? –  May 03 '17 at 13:28
  • Help me... please –  May 03 '17 at 13:54
  • If you want any further explanation you must give much more detail about the problem you are trying to solve. Not just one equation, but all the information about what each thing in the equation means and what larger problem this is supposed to solve. Also, to write the formulas so that people can understand them, start here: https://math.stackexchange.com/help/notation – David K May 03 '17 at 13:58
  • Does anyone help me? –  May 03 '17 at 17:14

1 Answers1

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Momentum is usually defined as $$ M = r \times F $$ where $M$, $r$ and $F$ are vectors and $\times$ is the vector product.

$M$ is the resulting momentum vector, it is normal to the plane of a resulting movement, where a force $F$ acts on a point at a position given by the radial vector $r$.

animation

(Source: Wikipedia)

Right hand rule: Your thumb points in the direction of the vector $M$, your fingers show the direction of the resulting movement.

right hand rule

(Source: Wikipedia)

In the animation above you see the radial vector $r$ (red arrow), the attacking force $F$ (blue arrow), the resulting momentum $M$ (light blue arrow, pointing upwards=counter clockwise movement or pointing downwards=clockwise).

Further linear momentum $p$ (green arrow) and the angular momentum $L$ (light green arrow).

mvw
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