Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: thedoc on 08/06/2015 18:50:02

Title: How does angular momentum work?
Post by: thedoc on 08/06/2015 18:50:02

Abdullah Moosa  asked the Naked Scientists:
   Question on conservation of angular momentum

Regarding the famous demonstration of conservation of angular momentum using a person on a turntable holding a spinning bicycle wheel,  what happens to the initial angular momentum from spinning in a vertical plane once the person flips the wheel horizontally so that the turntable begins to rotate in the opposite direction of the wheel, leaving angular momentum from horizontal spinning zero as it was before? If angular momentum is to be conserved, should there not be a torque (perhaps not big enough) oriented to rotate the system in a vertical plane to restore the initial angular momentum? Thank youAbdullah


   

What do you think?

Title: Re: How does angular momentum work?
Post by: Integza on 26/08/2015 21:46:49

Hi ;) I'm Integza.

To be honest i didn't really understand your question, so i think if you watch this video about gyroscopic precession you doubt about the subject:

If the doubt persist, i ask you to reformulate the question.

Hope it was helpful.

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https://www.facebook.com/thisisintegza

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https://twitter.com/Integza__

Title: Re: How does angular momentum work?
Post by: PmbPhy on 27/08/2015 01:30:14

Quote from: thedoc on 08/06/2015 18:50:02

Abdullah Moosa  asked the Naked Scientists:
   Question on conservation of angular momentum

Regarding the famous demonstration of conservation of angular momentum using a person on a turntable holding a spinning bicycle wheel,  what happens to the initial angular momentum from spinning in a vertical plane once the person flips the wheel horizontally so that the turntable begins to rotate in the opposite direction of the wheel, leaving angular momentum from horizontal spinning zero as it was before? If angular momentum is to be conserved, should there not be a torque (perhaps not big enough) oriented to rotate the system in a vertical plane to restore the initial angular momentum? Thank youAbdullah


   

What do you think?

Angular momentum is conserved only on an isolated system, i.e. when forces don't act on the object(s). When you exert a force on the object then in general you're exerting a torque and torque changes the angular momentum of an object. When the person flips the object he has to exert a torque on the object and in doing so he changed the angular momentum.