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#1 2007-10-30 13:42:32

fusilli_jerry89
Member
Registered: 2006-06-23
Posts: 86

Quick Question About Vectors - Takes 2 seconds...maybe more

l = r x p for a rotating object

angular momentum = radius times perpendicular momentum

dl/dt = (dr/dt) x p + (dp/dt) x r
The book then says dr/dt equals the instantaneous velocity at that point, but how can the change in distance from the axis of rotation be the same as the change in circular distance?

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#2 2007-10-30 13:57:40

JaneFairfax
Member
Registered: 2007-02-23
Posts: 6,868

Re: Quick Question About Vectors - Takes 2 seconds...maybe more

r is a vector, not a scalar. If r has a fixed magnitude, its direction will still be changing; hence it still makes sense to talk of the rate of change of r with respect to t (change of direction if not of magnitude).

NB: In the equation l = r × p, × is vector product, not ordinary multiplication. Vector product is only defined for vectors, not scalars.

Last edited by JaneFairfax (2007-10-30 14:02:06)

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#3 2007-10-30 14:47:09

fusilli_jerry89
Member
Registered: 2006-06-23
Posts: 86

Re: Quick Question About Vectors - Takes 2 seconds...maybe more

Thanks!

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