This becomes obvious when one draws the lines of action for all of the forces on the yo-yo. String tension, gravity, normal force, and friction. For a demo, I would use a partially filled spool of wire (the larger the better) --much easier for students to see than a yo-yo.
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From: phys-l-bounces@carnot.physics.buffalo.edu [phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of Bill Nettles [bnettles@uu.edu]
Sent: Friday, September 10, 2010 11:23 AM
To: Forum for Physics Educators
Subject: Re: [Phys-l] line of action
Also, choose an instantaneous axis of rotation at the contact point of the yo-yo with the surface. The only torque about this point is provided by the tension of the string. Basically the same as your line of action.
-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of Quist, Oren
Sent: Thursday, September 09, 2010 1:36 PM
To: Forum for Physics Educators
Subject: Re: [Phys-l] line of action
"line of action" is the way to solve this problem. It has always been one of my favorite problems and demonstrations.
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