Quote:
Originally Posted by raaaid
wow thanks a lot outlaw as the goodie you are fighting for a bad cause you just gave it away:
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Everything you said is wrong.
The static friction coefficient (μ) between two solid surfaces is defined as the ratio of the tangential force (F) required to produce sliding divided by the normal force between the surfaces (N)
μ = F /N
So, the coefficient of friction is determined experimentally and DEPENDS ON THE SURFACES INVOLVED. That includes EVERYTHING about the surfaces and the bodies used in the aforementioned experiment.
The example coefficients of friction used in textbooks and even in industry are VERY BROAD. For example, for steel on steel sliding pipe supports we use a 0.3 coefficient of friction. This works because all of our supports conform to similar specifications AND they are about the same size. If we started using a support with a contact area on the order of 50'x50' instead of the order of 4"x6" we would need to look at our friction coefficients again.
So, THE EQUATION IS INDEPENDENT OF THE AREA OF CONTACT, but determining the coefficient of friction is not.
That is why, as I said before, the rolling and sliding friction equations are gross simplifications and must be used within their limitations.
--Outlaw.