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Coefficient of Friction
Name: Steve
Status: student
Age: 20s
Location: N/A
Country: N/A
Date: 2000-2001
Question:
I am currently enrolled in a College Level physics
class. The professor was talking about the coefficient of friction. I
asked if it could ever be greater than 1. He said it could. It didn't
make sense to me that this could be true, so I asked him to explain
it. He then ASSIGNED a value for M (coefficient of friction) of 5 and
put it into the formula N=Mf. I said he couldn't just insert a value for
M. He said he could. I asked him how could he derive such a value, he
got frustrated and said class was over and slammed his book closed. Can
you please give a detailed (and mathematical) explanation as to why the
coefficient of friction can't go above 1. (You may edit this question as
you see fit, as long as I receive a detailed answer.) THANK YOU VERY MUCH
Replies:
Perhaps it would be a more instructive exercise for you to try to prove that
a coefficient of friction CAN'T be greater than 1. All that such a number
would mean is that the frictional force resisting movement of an object
tangentially to a surface is greater than the force pushing the object into
the surface. Why doesn't it make sense to you that this is possible?
Richard E. Barrans Jr., Ph.D.
Assistant Director
PG Research Foundation, Darien, Illinois
The coefficient of friction CAN be more than one.
Friction is a force relating to molecular structure of two surfaces
touching each other. Molecules from one surface link with molecules from
the other. If you press the objects together more tightly, you push the
surfaces closer together, joining more molecules. This is why friction is
proportional to the "normal force", how tightly the surfaces have to push on
each other to keep from breaking. This proportion is the coefficient of
friction.
Molecules on adjoining surfaces just don't cling to each other strongly
enough to have a huge friction coefficient. Solid molecules prefer to cling
to each other rather than other solid materials. This is pretty much what
makes them solid. In theory, there may be some solid materials that cling
to each other strongly enough to have a huge coefficient of friction. I
just don't know of any.
Mellendorf
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