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Quoted:
Althought I just researched the answer and had no knowledge of it prior to this thread... I will agree with CSM based on what I have read in a the last few minutes.
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You ever doubted me? tsk. tsk. tsk.
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Ff=mu*F_normal.
This means the frictional force is equal to the coefficient of friction, denoted by lower case the greek letter mu, times the normal force. The normal force is always the force perpendicular to the surface. Think of it in terms of Newton's Third Law, every action has a reaction both equal in magnitude and opposite in direction. So if the block is sitting on a plane surface, and the mass of the block is 20kg, then the weight( a force quantity) is w=m*g, or 20kg*-9.8 m/s/s, which is about 196 Newtons. Now if there is a force of -196 newtons applied to the surface, but nothing is in motion, then the system is in equilibrium. This means that there must be an equal force of +196 Newtons acting upon the block by the surface, think of this as the normal force. It is a vector(a magnitude and direction) drawn perpendicular to the surface.
Sooooooo, this 196 Newtons is what we are interested in. In order for the block to move you need to overcome the frictional force, which we dont know, but we do know both elements required to calculate it, the coefficient of friction, and the normal force on the block. So all we have to do is multiply them. Ff= mu*Fn, or (.023)*(196Newtons). Notice that the coefficient of friction is a unitless quantity leaving us with a static frictional force of 4.508 Newtons, that must be over come before the object can move.
I can draw pictures or a free-body diagram if you require it.
It's more interesting if its on a slope.