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# Physics/Calculating static friction

Question
Hello Steve,

Thanks for volunteering on this site.
This is not a homework question - I am 36, and I am just interested in this for my own learning.
I am interested in calculating how much force is required to move an object and I am interested in friction in particular.
I found the following information on this website
http://easycalculation.com/physics/classical-physics/learn-static-friction.php

"A mass is resting on a flat surface which has a normal force of 98N, with a coefficient of  static friction of 0.35. What force would it take to move the object?  N = 98N, μs = 0.35

0.35 x 98N = 34.3N"

I think I have understood the general idea but I am just wondering about the friction coefficient. There are two objects involved here, and if each object has a different friction coefficient how is the value in this equation for the coefficient of static friction determined?
I already know the coefficient of friction given for materials in data sheets for the material each object is made of, but I can't seem to work out how to find the friction between the two objects.

Any advice you could help me with would be much appreciated!

Eddie

An 18 year old can tell me they're 36 here.  I'll judge for myself if it's a homework question based on the question and not your age.  Fortunately, this appears to not be a homework problem, but a misunderstanding.

There is one contact between the objects.  They have the same friction coefficient.  This is essential in one of Newton's laws, objects exert equal and opposite forces  upon one another.  There is no way to work out the coefficient of friction between two dissimilar objects, it must be measured.  The coefficient of friction for contact between objects made of material 1 might be one value, and between surfaces of material 2 might be another value...but neither value has much bearing on the coefficient of friction between materials 1 and 2.  Also, those values in the tables will depend on the condition of the surfaces, so don't trust them.

Physics

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#### Dr. Stephen O. Nelson

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