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Methods of Diminishing Friction

When the two surfaces are in contact with one another, one should be made harder than the other. Where there is much wear, it is customary to make one of the bearing surfaces of a material harder than the other. Thus the crank pins on steam engines are made of polished steel and turn in brass boxes, the friction between the brass and steel being less than it would be between two parts of steel.

Crank Pins on Steam Engine


Rolling friction is very much less than sliding friction, therefore, wheels are used on carriages, vehicles etc. It depends on some extent on the diameter of the wheels, friction being less when the diameter is greater.

 Wheels Reducing Friction



Did you know?

Static friction is ten times that of rolling friction.


But even when wheels are used there is sliding friction in the hubs. The resistance to the motion of the vehicle due to this sliding friction is diminished by making the axles of small diameter, but the length of its bearing surface does not affect the frictional resistance.



To avoid the friction due to the sliding between wheel and axle, ball bearings are used; but even in these bearings there is some sliding friction where adjoining balls rub against each other.

Ball Bearings


In some cases the axle is made to rest on the rims of two smaller wheels which are called friction wheels. This is a common practice in mounting grindstones.

Friction is greatly diminished by the use of lubricants, of which those most in use are oil, grease, soap and black lead. The substance used as lubricants covers or wets the surfaces so that the rubbing takes place between the original surfaces. When the bearing surfaces are subjected to great pressure, as in heavy machinery, a thick oil is used that is not driven out by the pressure; in very light machinery, as in clocks and watches, a very thin oil is used. If oil were used on wooden bearings it would only increase the friction, for it would soak into and swell the wood; dry soap or paraffin may be used as a lubricant for wood surfaces.

Lubricants Used in Wheels

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