Angular acceleration

  • Thread starter MHR-Love
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Main Question or Discussion Point

Hi guys,
supposing there is a collar which can freely move along a rod. If the rod is rotating with a certain angular velocity, the rod will move away from the rotating point (it can never move towards the point). The acceleration of the collar has a radial component toward the point, hence the radial force acting on the collar has a direction toward the rotating point.
My question is why are their directions towards the point while the motion of the collar is out??
when I pull a box, the box's acceleration will have the same direction as the my pulling force and so does its motion. What makes the collar analysis different?
Thnx
 

Answers and Replies

  • #2
nvn
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The two scenarios you mentioned are not different. They are the same. When you pull on the box, the box exerts a reaction force in the opposite direction, pulling back on you. Likewise, when you rotate the rod and collar, you are pulling on them toward the center point of rotation; and the rod and collar exert a reaction force in the opposite direction, pulling away from the center of rotation.

If you stop pulling on the box or the rod and collar, all of these objects will continue moving in a straight line, unless other forces change or stop them. Therefore, the box keeps moving toward you, and the rod and collar keep moving perpendicular to you, which is away from you.
 
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  • #3
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The two scenarios you mentioned are not different. They are the same. When you pull on the box, the box exerts a reaction force in the opposite direction, pulling back on you. Likewise, when you rotate the rod and collar, you are pulling on them toward the center point of rotation; and the rod and collar exert a reaction force in the opposite direction, pulling away from the center of rotation.

If you stop pulling on the box or the rod and collar, all of these objects will continue moving in a straight line, unless other forces change or stop them. Therefore, the box keeps moving toward you, and the rod and collar keep moving perpendicular to you, which is away from you.
Thnx for replying, I thought of your answer by imagining that I am rotating a ball of mass m using a string attached to it, so I feel like my hand is pushed away because of this reaction. Thnx and happy day
 

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