Wheels Reduce Friction

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Sliding Friction

It is the frictional force that opposes the relative sliding motion between the two surfaces in contact. It simply means that if an object is in motion on a surface, the frictional force that is offered by the surface is called sliding friction.

The keywords here are sliding motion. The two surfaces have to be in relative motion with

each other. As there’s movement involved, this force is also called kinetic friction.

For example, when a box is moving on the table, it is in relative motion with respect to the table. The resistive force applied by the table when the box is moving is called sliding friction.

Rolling Friction

It is the resistive force offered by any surface which opposes the rolling motion of any object that rolls over it. It is a force associated with rotational motion.

The resistance offered by rolling friction is usually less than that offered by sliding friction. Therefore, it is easier to roll an object than to slide the same object.

It is difficult to drag or slide heavy luggage because of sliding friction. But when wheels are attached to the luggage it becomes easier to roll it because rolling friction is lesser than sliding friction.

Another example where the concept of rolling friction is used to reduce friction is the ball bearings. They are spherical metal balls used in many mechanical structures having moving parts. They’re generally made of stainless steel, brass or ceramic. They reduce friction to a great extent which in turn reduces the wear and tear of machine parts.

Summary