The following laws of sliding friction have been established experimentally:
1. Total friction is propotional to normal pressure.
This means that force of friction comprises a certain part of normal pressure and can be expressed by the equation
F/Q=f,or F=fQ
The factor f represents the coefficient of sliding friction, or the coefficient of friction of the first type.
2. The force of friction does not depend on the area of contact.
Also, the force of sliding friction does not depend on the specific pressure.
3. If normal pressure is unchanged, total friction will depend on the material of the contacting bodies, the finish of their surfaces and the nature and amount of lubrication.
4. Total friction does not depend on the sliding velocity, although the force necessary at the start of sliding is greater than when momentum (retained motion) has been achieved.
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