Coefficients of Friction

Materials	Coeff. of Static Friction _s	Coeff. of Kinetic Friction _k
Steel on Steel	0.74	0.57
Aluminum on Steel	0.61	0.47
Copper on Steel	0.53	0.36
Rubber on Concrete	1.0	0.8
Wood on Wood	0.25-0.5	0.2
Glass on Glass	0.94	0.4
Waxed wood on Wet snow	0.14	0.1
Waxed wood on Dry snow	-	0.04
Metal on Metal (lubricated)		0.06
Ice on Ice	0.1	0.03
Teflon on Teflon	0.04	0.04
Synovial joints in humans	0.01	0.003

Source: Serway Physics for Scientists and Engineers 4th edition (p. 126.)

'If you would be a real seeker after truth, it is necessary that at least once in your life you doubt, as far as possible, all things.'

René Descartes
(1596-1650)