# Coefficient of friction

1. Jun 2, 2005

### darnone

hi, im doing a physics project in which im building a hovercraft. i want to show mathematically how the craft lowers the friction, however, i cannot find the coefficent of friction for air. i found the coefficient of friction for concret on rubber to be roughly 0.8.... any ideas on air? thanks alot for any help.

2. Jun 3, 2005

### OlderDan

You probably will not find it. Coefficient of friction applies to solid materials in contact with one onother. When fluids are involved, resistance effects are more likely to fall in the realm of viscosity. "Thick" liquids pour slowly, and they resist motion more than thin liquids. Gasses offer far less resistance than liquids. The resistance force on a solid moving through a fluid depends on the speed of motion. The reason a skydiver reaches a terminal velocity is because of the viscosity of air. You might do some searching for information related to that term.

3. Jun 3, 2005

### morry

Yep, a fluid dynamics text book would be very handy here. Perhaps you could find some data on google.