Whenever one surface moves over another, a force is set up which resist the movement.This force, which we call friction always opposes motion.It exists in every machine.It can be reduced by lubrication but never completely removed.In general, the force opposing motion is slightly greater before one surface starts moving over another surface than after movement has started.This slightly greater force is called static friction.The force which must be overcome to keep one surface moving over another is known as sliding friction.Static friction is greater than sliding friction.
The value of sliding friction depends on the nature of the two surfaces which touch each other.Thus friction between two rough planks can be lessened if they are made smooth.Sliding friction is independent of the area of surface in contact.In theory a small brake pad will exert as much braking force as a large one of greater surface area.In practice a small pad will wear down more quickly and therefore is not used.One other law of friction should be noted.We can make normal reaction between two surfaces in contact twice as large by doubling the mass carried by one surface.If we do so we find that sliding friction between the surface is also doubled.If we halve the mass carried, sliding friction is also halved.This shows that sliding friction is proportional to the reaction between the surface in contact.
Hiç yorum yok:
Yorum Gönder