Re: moment of inertia

From: Uncle Al (UncleAl0_at_hate.spam.net)
Date: 02/08/05 

Date: Tue, 08 Feb 2005 09:07:10 -0800

Bluethunder wrote:
>
> ok, it's me again, the guy who hasn't touched physics for 30 years and I am
> not shy in asking questions.....
> Can someone give me a hint of what moment of inertia is? I know it is mr^2.

The exact expression depends on the shape of the rotating body and
where the axis of rotation is located and oriented. Consider a long
thin rod rotating about its long axis, off-center; normal to its long
axis at its center of mass, attached at its far end...
 
> I just don't know (or don't remember) what it is. Does it help something
> spin faster or does it prevents something from spinning faster? When a
> skater brings her arms in and she spins faster (with smaller radius). Is it
> the moment of inertia that helps her go faster? Why is it then, the radius
> is smaller? A ring will has greater M-o-I while a solid disk of the same
> radius has smaller M-o-I. But a solid disk will roll down a hill faster
> than a ring. So, it seems M-o-I prevents something from spinning faster.
> Am I wrong here?

   1) Energy is conserved.
   2) Linear and angular momenta are conserved.
   3) As a given system is deformed non-conserved quantities will vary
to be consistent with (1) and (2). 

-- 
Uncle Al
http://www.mazepath.com/uncleal/
 (Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf

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