# How to find the coefficient of static friction.

1. Oct 23, 2012

### mateye10

1. The problem statement, all variables and given/known data
In order to hold a book of mass m stationary against a wall, you must push horizontally with a force of at least P.
a. make a force diagram and find the coefficient of static friction
b. calculate the coefficient of static friction for the wall and book when at least a 35-N horizontal push is needed to hold a 1.2-kg book steadily at rest against the wall.

2. Relevant equations
F=ma
F_n=mg
F_f=μF_net
3. The attempt at a solution
I find it difficult to grasp the concept that, somehow, there is still friction between the wall and the book even though there is no velocity. My best guess would be:

F_f = F_net so μ would have to equal 1. help would be greatly appreciated.

2. Oct 23, 2012

### Flipmeister

If there is no velocity and no acceleration, the system is in equilibrium. Try drawing the force diagram without the static friction and then you'll see how friction plays a role.

3. Oct 23, 2012

### mateye10

so is friction equal to weight?

4. Oct 23, 2012

### Flipmeister

Yes, and knowing that and the basic equation of static friction (f=μ*n), you can now calculate μ.

5. Oct 23, 2012

### mateye10

great, I see. thank you so much.