# Coefficient of friction

1. Feb 3, 2010

### zubbylight

1. The problem statement, all variables and given/known data
Why do brakes and clutches need high coefficient of friction?

2. Relevant equations

Pls give applications where engineers need to have materials having low values for the coefficient of friction

3. The attempt at a solution

2. Feb 3, 2010

### poporo

Friction is very important for both Brakes and clutch pads. Given that friction is a measure of how hard it is to slide one object over another, brake pads slow the speed of wheels down by pushing against a spinning disc. The higher the coefficient of friction, the harder it is for the disc to continue spinning against the pad. Therefore if no more work is put into spinning the disc (lifting one's foot off the gas pedal), friction will cause the disc to stop spinning when the brake pad is applied. The higher the coeff. of friction, the faster the car can brake.

I'm not too keen on how clutches work, but this article should explain everything just fine: http://auto.howstuffworks.com/clutch1.htm

3. Feb 3, 2010

### zubbylight

thank you all for ur contributions... really appreciate it.
Cheers

4. Feb 4, 2010

### pongo38

some bridge bearings need to be sliding joints, requiring a low coefficient of friction. PTFE is often used.