# Explain the principle of belt friction?

Belts are used to mechanically link two or more rotating items. They may be used as a source of motion, to transmit power at up to 98% efficiency between two points, or to track relative movement.

As a source of motion, a conveyor belt is one application where the belt is adapted to continually carry a load between two points. A belt may also be looped (or crossed) between two points so that the direction of rotation is reversed at the other point.

Power transmission is achieved by specially designed belts and pulleys. The demands on a belt drive transmission system are large and this has led to many variations on the theme.

Friction is the force that opposes the relative motion or tendency toward such motion of two surfaces in contact. It is not a fundamental force, as it is made up of electromagnetic forces between atoms. When contacting surfaces move relative to each other, the friction between the two objects converts kinetic energy into thermal energy, or heat. Friction between solid objects and fluids (gases or liquids) is called drag.

Kinetic (or dynamic) friction occurs when two objects are moving relative to each other and rub together (like a sled on the ground). The coefficient of kinetic friction is typically denoted as μk, and is usually less than the coefficient of static friction. From the mathematical point of view, however, the difference between static and kinetic friction is of minor importance: Let us have a coefficient of friction which depends on the sliding velocity and is such that its value at 0 (the static friction μs ) is the limit of the kinetic friction μk for the velocity tending to zero. Then a solution of the contact problem with such Coulomb friction solves also the problem with the original μk and any static friction greater than that limit.

Since friction is exerted in a direction that opposes movement, kinetic friction usually does negative work, typically slowing something down. There are exceptions however, if the surface itself is under acceleration. One can see this by placing a heavy box on a rug, then pulling on the rug quickly. In this case, the box slides backwards relative to the rug, but moves forward relative to the floor. Thus, the kinetic friction between the box and rug accelerates the box in the same direction that the box moves, doing positive work.
In the fictional universe of Robert E. Howard's Conan the Barbarian, Bêlit is a pirate queen who has a romantic relationship with Conan. Her name may have been taken from Bel, god of thieves in her native land of Shem. She appears in Howard's Conan novelette "Queen of the Black Coast", first published in Weird Tales 23 5 (May 1934).

The character Valeria featured in the 1982 movie Conan the Barbarian borrowed some aspects of Howard's Bêlit, such as vowing to return from the dead to save Conan..

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