The term “coefficient of friction” refers to a dimensionless constant that represents the ratio of the force of friction between two bodies to the force pressing them together. There are two main types of coefficients of friction:
Coefficient of Static Friction (μs):
- This coefficient represents the ratio of the force of static friction to the normal force when two objects are at rest and an external force is applied, trying to initiate motion.
- The formula for static friction is Fs≤μsN, where Fs is the force of static friction, μs is the coefficient of static friction, and N is the normal force.
Coefficient of Kinetic Friction (μk):
- This coefficient represents the ratio of the force of kinetic friction to the normal force when two objects are already in motion.
- The formula for kinetic friction is Fk=μkN, where Fk is the force of kinetic friction, μk is the coefficient of kinetic friction, and N is the normal force.
Daily Life Examples of Coefficient of Friction
| Material Pair | Static Friction (μs) | Kinetic Friction (μk) |
|---|---|---|
| Rubber on Dry Concrete | 0.7 – 1.0 | 0.6 – 0.8 |
| Wood on Wood (Dry) | 0.3 | 0.2 |
| Metal on Metal (Lubricated) | 0.15 | 0.06 |
| Ice on Ice | 0.1 | 0.03 |
| Glass on Glass (Dry) | 0.9 | 0.4 |
| Teflon on Teflon | 0.04 | 0.04 |
| Aluminum on Steel (Dry) | 0.61 | 0.47 |
| Cork on Wood | 0.4 | 0.3 |
| Leather on Wood | 0.5 | 0.4 |
| Concrete on Concrete | 0.6 | 0.5 |
