Conservation of Angular Momentum

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Angular momentum is conserved about point A because the effects of external forces, like gravity, are negligible during the brief duration of a collision. The integral of the moment of forces about point A is zero, indicating no net external torque acts during this short time. Therefore, the angular momentum before the impact equals the angular momentum after the impact. This assumption allows for simplifications in analyzing the system. The discussion highlights the importance of time scales in the conservation of angular momentum.
eurekameh
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Why is angular momentum conserved about point A? I know that integral(M,A dt) = H,2A - H,1A, where M,A is the moment of all forces about point A, H,2A is the angular momentum about point A after the impact and H,1A is the angular momentum about point A before the impact. If angular momentum was conserved, it would mean that integral(M,O dt) = 0. In the problem, however, there is a weight that is causing a moment about point A. Why is this ignored?
 
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eurekameh said:
In the problem, however, there is a weight that is causing a moment about point A. Why is this ignored?
They are assuming that the collision takes only a very short time--so any effect of gravity can be ignored during the collision. The angular momentum about A immediately before the collision equals the angular momentum about A immediately after the collision.
 

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