# Friction for different contacts

1. Feb 26, 2013

### sriram123

Hi all,
I know this is a very basic question and has been discussed in various threads.Anyway i would i like to ask this.

If the value of friction only depends on coefficient of friction and normal force, why is rolling friction less than sliding friction? Is it because the value of Rn the reaction force changes?

I know this is very elementary but I thought it would make my understanding better.

2. Feb 26, 2013

### tiny-tim

hi sriram123!
"rolling friction" isn't actually friction, it's a loss of energy caused by continual deformation of the wheel where it meets the surface

from the pf library:
Friction:

Friction at the point of contact of a rolling body is static friction.

There is also a rolling resistance, or "rolling friction": an additional small force, caused by deformation of the body (in exam questions it can usually be ignored).

Friction at the point of contact of a sliding body is of course dynamic friction.