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Re: Favorite Test Questions

On Thu, 12 Mar 1998, Dr. William Newbolt wrote:

Date: Wed, 11 Mar 1998 19:20:37 -0500
Reply-to: phys-l@mailer.uwf.edu
From: Jerome Epstein <jerepst@worldnet.att.net>
To: phys-l@atlantis.uwf.edu
Subject: Re: Favorite Test Questions


The spinning wheels AT THE STARTING LINE undergo kinetic
friction from the time that they start spinning until
that race car comes to a full stop at the end of the
drag race.

I'm afraid this is just not true.

Kinetic friction is involved with the rear tires as long as they are
slipping. The do slip for a large fraction of the trip. Furthermore, the
coefficient of kinetic friction is greater than 1!


J. Epstein
There is a lot of good physics here. If nothing else, this
problem can give us an appreciation for the limitations of
the empirical law of friction. An example: The wide
tread used on dragsters gives me the feeling that they
don't really believe that the force of friction
is independent of the area of contact.

I don't know whether the force of friction is dependent on the area, but
the amout of wear certainly is. The tread of a narrow tire would have to
be much thicker than on a wide tire not to be worn through during a single
run.


In my opinion we need to point out that the laws of
friction are empirical laws which are frequently useful for
modeling a particular mechanical system.
Barlow Newbolt

There is a huge amount of physics and engineering in auto racing and drag
racing in particular. Does anyone know where we can get data (I believe
it exists, but the owners may not want to share it!) such as acceleration,
speed, torque, horsepower, down force due to spoiler, etc. as a function
of time for a highest performing dragster? I once tried briefly searching
the web for such info. but came up empty.

bob
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