# Friction and gravity

1. Jun 25, 2013

### nil1996

What is the relation between friction and gravity?Is friction independent of gravity?

2. Jun 25, 2013

### genxium

Would you please make the statement more clear? If the question is involving high school physics problems, I would say that $\text{friction is proportional to pressure not gravity, given a certain coefficient of friction} \; \mu.$

3. Jun 25, 2013

### CWatters

Friction is pretty complicated. Several assumptions are usually made to try and simplify it. For example..

Friction is independent of velocity
Friction is independent of surface area
Friction is proportional to the normal reaction force (eg weight)

The normal force is the mass * acceleration due to gravity so in short yes, the max friction force depends on gravity.

EDIT: Astronauts using a treadmill in space have to be pulled down onto it using springs/elastic.

Last edited: Jun 25, 2013
4. Jun 25, 2013

### CWatters

5. Jun 25, 2013

### nil1996

thanks

thanks for all your replies.You are helping me a lot.