A-level Maths Mechanics Question
Hi, Can someone please explain why mu, the coefficient of friction, has a range of values? I thought it was constant? I understand F max is the maximum frictional force between two surfaces, and mu*R finds this, but I still don't understand the range of values. Any help greatly appreciated. Sorry I accidentally named the files the wrong way round.
(edited 1 year ago)
Original post by mqb2766
48//61 will be the limiting value, but if its larger than that then equilibrium will still be maintained.
As you say muR is the maximum frictional force, so if this maximum is larger than the required force, its still in equilibrium.
As you say muR is the maximum frictional force, so if this maximum is larger than the required force, its still in equilibrium.
But surely we can say that because the body is in equilibrium, the horizontal forces must be equal, and therefore we can say that we know the value of mu? I'm still a bit confused though - surely mu and R would be constant and wouldn't change as the opposing force changes? But one or both must change because Friction, mu*R, changes
(edited 1 year ago)
Original post by Har6547
But surely we can say that because the body is in equilibrium, the horizontal forces must be equal, and therefore we can say that we know the value of mu? I'm still a bit confused though - surely mu and R would be constant and wouldn't change as the opposing force changes? But one or both must change because Friction, mu*R, changes
The net force is zero because the body is in equilibrium, however friction is like a sponge:
|friction force| <= mu R
Equality only holds in the limiting case. You could think of the required frictional force necessary to maintian equilbirium as being the difference (signed sum) of the other forces, so overall they would sum to zero.
So as long as muR is greater than or equal to the (magnitude of the) required frictional force to maintain equilibrium, it will be in equilibrium. Just think that if the plane/peg was wood say and it was in (limiting) equilbirum, but then the wood was replaced with rubber which has a much greater coeff of friction, youd still be in equilibrium. So as long as the coefficient of friction is greater than or equal to the limiting case, it will still be in equilbrium.
(edited 1 year ago)
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