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Come On People!
The problem is for a freshman level physics class.
"A ball rolls down an inclined plane without slipping. Given the
from which it starts, find the speed of the ball at the bottom of
In your attempts to be "absolutely perfect" you wish to include the
"internal friction" energy dissipation,
"ADHESION of the wheel with the table makes a difference".
"Also, if the rolling object and the flat surface are both
as the object rolls along, we'd see "electrification by contact."
rolling object would aquire a constantly increasing surface charge,
would leave behind a trail of opposite surface charge. Some of the
work going into the "rolling friction" would be stored as
No one has mentioned "air resistance" yet, but that's about all
Do wish to use a velocity squared resistance, or cubed, or some
We wonder why students see physics as hard. Yet, some insist on
very simple problem and then making is so complicated that the
freshman student throws up his hands and decides to major in
A student with a stopwatch, ball, and inclined plane will never
effects. Even a computerized timer of some kind will not allow
enough measurements to be sure. Don't take a nice simple experiment
complicate it to a degree that can only frustrate the student.
Physics is a "science of approximations." We can be as accurate and
as we want to be. But, we should not be more accurate than has
a specific case. Students need to see the simplicity and elegance
physics without getting totally bogged down in unneeded details.
these for the more advanced classes.
I don't know if anyone is still reading, but I know I feel better
this off my chest.
Oren Quist, SDSU
From: kowalskil [mailto:kowalskil@MAIL.MONTCLAIR.EDU]
Sent: Thursday, June 28, 2001 11:58 AM
Subject: Re: Conservation of ME and nonconservative forces
I remember seeing the following argument about rolling
friction. Consider a wire which is bent and unbent many
times. Its temperature goes up. A rolling object is not
perfectly rigid; it is compressed and decompressed
constantly along diameters as they become parallel to
the normal reaction force. The so-called "internal
friction" is a dissipation mechanism to be considered.
William Beaty wrote:
On Wed, 27 Jun 2001, Paul O. Johnson wrote:
There is indeed no slipping, Oren, so there is no KINETIC
rolling. Itit seems to me that there must be STATIC friction to cause
indeedalso seems to me that the instantaneous point of contact is
train, butmoving down the plane, opposite to the static frictional force.
Therefore, the frictional force does negative work, converting
potential energy to thermal energy.
I don't know if it would be significant for something like a
for small tabletop objects the ADHESION of the wheel with thetable makes
a difference. Imagine trying to roll a steel ball across a glassinsulators, then
tabletop. Now imagine that the glass has a very thin coating of
half-dried rubber cement...
Also, if the rolling object and the flat surface are both
as the object rolls along, we'd see "electrification by contact."The
rolling object would aquire a constantly increasing surfacecharge, and it
would leave behind a trail of opposite surface charge. Some ofthe
work going into the "rolling friction" would be stored ase-fields.
((((((((((((((((((((( ( ( ( ( (O) ) ) ) )
William J. Beaty SCIENCE HOBBYISTwebsite
EE/programmer/sci-exhibits science projects, tesla, weirdscience
Seattle, WA 206-789-0775 freenrg-L taoshum-L vortex-Lwebhead-L