Friction Calculator
Friction force from the coefficient and normal force.
The model
f = μ × N
Friction is proportional to how hard the surfaces press together, and, surprisingly, independent of contact area: wide tires don't grip more by area but by rubber chemistry. Static μ (before sliding) beats kinetic μ (while sliding), which is why ABS brakes that avoid lockup stop shorter.
Typical coefficients
Rubber on dry asphalt 0.7 (wet 0.4), steel on steel 0.6, wood on wood 0.35, waxed ski on snow 0.1, ice on ice 0.05, and teflon on anything about 0.04. That spread, times your weight, is the difference between walking normally and the penguin shuffle.