# Explain friction problems?

1. Dec 4, 2003

### curlydafatboy

could sum1 PLEASE explain friction problems? (hs level) for example: a 10 N block is sliding down a ramp at 30 degrees, wat is da force of frction (approx) PLEASE help, i got test 2 morrow

2. Dec 4, 2003

### chroot

Staff Emeritus
The force due to friction is

$$F = \mu_k N$$

where $\mu_k$ is the coefficient of kinetic friction and N is the normal foce -- the component of the weight of the object pushing down on the ramp vertically. When the ramp is horizontal, all the weight of the object pushes on it. As the ramp gets steeper and steeper, less of the weight of the object pushes on it, and thus there is a smaller friction force.

The normal force between a mass of m kilograms on a plane at an angle $\theta$ to the horizontal is

$$N = m g \cos \theta$$

Thus the force due to friction for a mass m on a plane at angle $\theta$ to the horizontal is

$$F = \mu_k m g \cos \theta$$

- Warren

3. Dec 4, 2003

### curlydafatboy

thank u so much

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