Re: [Phys-l] Turning effects of a moving bike

["Bob Sciamanda" <trebor@winbeam.com>]

It is easily shown (see any intermediate mechanics text) that the 
"Torque=dL/dt" theorem, applied to a system, holds for the CM of a system as 
origin, regardless of the motion of the CM.

Bob Sciamanda
Physics, Edinboro Univ of PA (Em)
trebor@winbeam.com
http://www.winbeam.com/~trebor/
----- Original Message ----- 
From: "John Denker" <jsd@av8n.com>
To: "Forum for Physics Educators" <phys-l@carnot.physics.buffalo.edu>
Sent: Tuesday, August 19, 2008 2:41 PM
Subject: Re: [Phys-l] Turning effects of a moving bike


> On 08/19/2008 08:35 AM, Bob Sciamanda wrote:
>
> > The point of contact between tire and road is NOT an inertial origin.
> > Torques relative to this accelerating origin are not equal to the time 
> > rate
> > of change of system angular momentum.
>
> That's all true, and it's good advice in general ... but I don't see
> how it answers the question.
>
> The way I read the question, it asked why using the center of mass
> was /different/ from using the contact point as the datum.  I don't
> see how mentioning "non inertial" explains the /difference/.  Neither
> the CM nor the contact point is inertial.
>
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