what is the theories of effects of friction?&example of effects of friction?

Answer 1

The important laws of friction also known as Coulomb's laws of friction are:

1. The frictional force is directly proportional to the normal force between the surface at which it acts.
(Force required for pulling a block, initially at rest, over a surface is double of that required for pulling another block, of mass twice as the former and initially at rest, over the same surface is double.)

2. Frictional force always acts in a direction opposite to the direction of motion or tendency of motion.
(If a body is moving relative to another body in contact, then the frictional force acts on both the bodies. It acts on each body in the direction opposite to that of its motion. As the two bodies are in relative motion so the direction of motion of the first with respect to the second and that of the second with respect to the first are always opposite. So the frictional force acts on the two bodies in opposite directions.)

3. The frictional force on a surface is always perpendicular to the normal force.
(A box can be held over a vertical wall by exerting a force in a direction perpendicular to the wall because the frictional force, perpendicular to normal force, acts in the vertically upward direction thus resisting the downward motion of the box.)

4. Fluid friction is less than solid friction.
(So liquid lubrication is done in bearings to minimize friction and hence to reduce wear.)

5. In solid friction, rolling friction is less than sliding friction.
(So it is dificult to pull a cycle with brakes on than without it as when the brakes are on the type of relative motion between the wheel and the road is of sliding type.)

6. The magnitude of frictional force is independant of the area of contact between the surfaces in relative motion.
(The force required to move two blocks, initially at rest, of different shapes and sizes but with same mass over a particular surface is same. But for two blocks, initially at rest, with different masses but same area of contact with the surface on which they move the force required to move the one with greater mass is more.)

7. Coefficient of solid friction is independent of temperature.
(The force required to pull a block resting on a surface does not change with temperature.)

8. Static friction is always greater than kinetic friction.
(The force required to move a body, initially at rest, over a surface is more than that to keep the same body, initially in motion over the same surface, in moving condition.)

Answer 2

Well, friction is the force that is encountered by any object that is in motion. The amount of force can be approximately calculated by taking the component of force that is acting 90º to a surface and multiplying it by some friction factor.

A common way that friction theories are used every day is in the investigation of traffic accidents. When a tire is locked and skidding, the only thing that is slowing it down is the force of friction. Thus, the length of skid marks is directly proportional to the speed of a vehicle. The speed of a vehicle involved in an accident is an important factor in deciding who is at fault and if they can be charged with more things in an accident.

Answer 3

You can study the effects of friction on many levels including tribology (by tribologists). Trials and tribulations deal with the friction between people but tribologists are generally interested in friction and lubrication. If you use a very powerful microscope to examine most material surfaces you will see an endless range of "mountains" in every direction. If you place two such surfaces together and move one relative to the other, the mountain peaks interfere and anctual shear each other off (or at least the hard mountains shear the soft ones). This causes an intense release of energy at the sheared mountain that is manifested as heat. Too much heat can cause increased destruction of the mountain peaks (perhaps by softening them). Lubrication (especially grease) fills the valleys between mountain peaks allowing the two surfaces to slide past each other on an ocean of large grease molecule that shear with very little resistance and minimal heat generation. Grease is usually a mixture of soap and oil and is much thicker than oil. Oil also provides good lubrication by adhering to the molecules of both surfaces such that oil molecules slide past oil molecules as the surfaces move. Often more heat is generated with oil than with grease (especially if the parts move more rapidly) and the oil can be circulated to an oil cooler to get rid of the excess heat.

Answer 4

Friction makes things not want to rub together so much. The get hot. If you make certain material really cold then they have no friction and stuff will simply fall through it, because there is no reactivitiy on the atomic level. There for eskimos do not make good bed mates