# Kinetic friction problems

1. Mar 10, 2008

### Brainv2.1beta

I am trying to create a 3d physics simulation and the first "problem" I have encountered is implementing realistic friction. Now, I was told by some professor that the faster an object is traveling the less friction that it has, however, I have not been able to find the appropriate equation/s on the net. I know the basic friction equation, F=uN. However, this is only useful for static applications; I need to learn the formula for kinetic friction, and how to apply it to non-static variables (eg. speed-=frictionequation.)

2. Mar 10, 2008

### Staff: Mentor

In the usual ("standard" or Coulomb) model for dry friction between surfaces, kinetic friction is given by $\mu_k N$ and is independent of velocity. When you start adding in air resistance you'll quickly get speed-dependent forces.

3. Mar 10, 2008

### Brainv2.1beta

So your saying that professor I mentioned was incorrect? At least this makes coding easier.

By the way, I am making rolling sphere physics.

Last edited: Mar 10, 2008
4. Mar 10, 2008

### Staff: Mentor

Why don't you ask the professor what he meant?

5. Mar 10, 2008

### Brainv2.1beta

Can't, I talked with him last at a science convention overseas.

6. Mar 10, 2008

### Staff: Mentor

Then pick up any freshman physics book and read what it says about kinetic friction.

7. Mar 10, 2008

### Brainv2.1beta

Yeah yeah I'm not in school anymore though and the library's a long walk...google doesn't really count...