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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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