Date: Fri, 25 Oct 2002 13:27:57 -0500

Author: "Karl I. Trappe"

Subject: Re: Rolling Objects and size

Post:

One of the problems with comparing like shaped objects (for example,
solid cylinders)to observe that their speed does not depend on the
radius is that you've got to decide what part of the object you are
comparing.

Generally, you start two objects with their centers of mass aligned
(a finger on top of each), then let them race to the bottom.
Whichever crosses the finish line first was going the
fastest...whoops...that means you observed the one with the larger
radius as getting there first (since in actuality it started out
ahead by the difference in radii. Generally a starting board that is
taller than the largest radius will take care of this.

Another potential pitfall is that the rolling friction may be
different because of the way the surfaces contact at sharper or more
shallow radii. It may also be different because you chose different
materials in order to get the "different masses" for showing that
mass was not a consideration, ie, you made a 2 inch cylinder of
brass, aluminum and steel bar stock.

Karl

--
Dr. Karl I. Trappe Desk (512) 471-4152
Lecture Demonstration Office Office (512) 471-5411
Physics Department, Mail Stop C-1600 Home (512) 264-1616
The University of Texas at Austin
Austin, Texas 78712-1081

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