Re: pinhole Center of Mass?

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From: pauld@exploratorium.edu
Date: Wed Nov 13 2002 - 18:44:33 PST 

Message-Id: <200211140244.gAE2iWa21459@isaac.exploratorium.edu>
From: pauld@exploratorium.edu
Subject: Re: pinhole Center of Mass?
Date: Wed, 13 Nov 2002 18:44:32 US/Pacific

Hi Marc

It is a center of mass and torque demonstration.

Gravity acts downward through the center of mass.

A normal force acts upward on each wheel perpendicular to the inclined plane.

Friction forces act parallel to the surface and opposite the motion of the cart
through the centers of the contact areas of the two locked wheels.

Friction forces act on the rolling wheels but only in a direction parallel to the
axle.

These vector forces times their distance from any reference point gives a net
torque on the cart.

The torque twists the cart in the direction you describe.

More explanation requires a diagram, want more?

Paul D

> I should konw the answer to this but I seem to be
> drawing a blank. I have a video demonstration of a
> cart sliding down an inclined plane first with its
> back wheels locked (cart slides down normally) and
> then with its front wheels locked (cart skids around
> until the locked wheels are in back). What's going on?
> Is this a center of mass phenomenon?
>
> -Marc
>
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