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April 23rd, 2017, 04:06 AM   #1
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rate of angular momentum of a point

Hi,

Does anyone know how to calculate the rate of angular momentum of a point,Q? Google is not helping me right now.

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April 23rd, 2017, 04:33 AM   #2
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Depends on the problem statement ... you have a specific one in mind?
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April 23rd, 2017, 05:05 AM   #3
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I need to find the rate of angular momentum of the centre of mass. Its for a biped robot.
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April 23rd, 2017, 06:17 AM   #4
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Quote:
Originally Posted by BrainFart View Post
I need to find the rate of angular momentum of the centre of mass. Its for a biped robot.
this is still a rather general statement ... angular momentum is usually measured relative to an axis of rotation or a specific position in space. In general, the angular momentum of a point mass relative to some other point is the cross product of the point mass's position vector and its linear momentum.

$\vec{L} = \vec{r} \times \vec{p} = \vec{r} \times m\vec{v}$

Also, you do understand that angular momentum and rate of change of angular momentum are two different things?
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April 23rd, 2017, 07:44 AM   #5
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I beg your pardon, I do mean the rate of change.

Am I right in thinking to get the rate of change you could take the derivative with regards to time of your above equation?
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April 23rd, 2017, 08:16 AM   #6
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the time rate of change of angular momentum is net torque ...

$\dfrac{dL}{dt}=\tau_{net}$
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April 23rd, 2017, 10:19 AM   #7
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Thank you
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