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# Mechanics 1: When to use Fmax and when to use just F (friction)? watch

1. I'm currently studying "Dynamics of a particle moving in a straight line", chapter 3 in my M1 Edexcel textbook.

Anyways, when should I be showing that I am calculating Fmax or F?

I know Fmax = uR (where u is 'myoo').

Am I right in saying, in an exam, I should show that I am calculating Fmax when there is acceleration of the particle in the opposite direction, or when the opposing force (e.g. tension) is equal to Fmax? So tension is equal to the limiting value:

Fmax >= uR

Is that right?

Thank you
2. The magnitude of the frictional force can take a range of values. F<=μR
If an object is in limiting equilibrium - it means that the object is on the verge of moving - it is staying still but the frictional force is at a maximum and any more forward force will overcome the frictional force and the object will start moving/accelerating. If an object is moving then the frictional force will be at a maximum.
In an exam you could state that since an object is not stationary then you know that the friction takes a maximum value.

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Updated: October 27, 2015
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