# Homework Help: Static friction at its maximum in relation to the magnitude of the applied force?

1. Jan 9, 2012

### celiachu

1. The problem statement, all variables and given/known data

Which of the following statements are true about Fs, max in the equation mu=Fs, max/Fnormal?

I. Fs, max is exerted perpendicular to the surfaces in contact.
II. Fs, max represents the maximum value of the force of static friction.
III. On a level surface, the magnitude of the Fs, max equals the magnitude of the applied force that starts the object moving.

2. Relevant equations

mu=Fs, max/Fnormal?

3. The attempt at a solution

Well, I know that Friction is parallel to the surface and opposite to the direction of the force on the object, so I is out of the picture, and II seems a bit obvious, so that's one true answer. I'm not understanding the third one, though. Help? I just need an explanation to III to know if it is true or false.

2. Jan 9, 2012

### sandy.bridge

The maximum static friction will be at the instant just before the object starts to move. For example, if
$$F_{S, max}=12.000000000$$, then I would assume $$F=12.000000001$$ would be suffice to induce movement, which is essentially 12.