what are the units
2006-08-12 04:30:10 · 10 answers · asked by Anonymous in Science & Mathematics ➔ Engineering
Hi, the unit is μ pronounced Meuw
The resistance to lateral motion when one attempts to slide the surface of one object over another surface is called friction or traction. The force of friction depends on the normal force, which is the force pressing the two surfaces together. It also depends on the types of materials from which the surfaces are formed--some materials are more slippery than others. The coefficient of friction is a measure of the slipperiness between two surfaces: the larger the coefficient of friction, the less slippery the surfaces. For example, pulling a heavy wooden block (large normal force) across the floor requires more force than does pulling a light one (small normal force); and pulling the wooden block along on a surface of rubber (large coefficient of friction) requires more force than pulling the same block along on a surface of ice (small coefficient of friction).
For a given pair of surfaces, there are two types of friction coefficient. The coefficient of static friction, μs, applies when the surfaces are at rest with respect to one another, while the coefficient of kinetic friction, μk, applies when one surface is sliding across the other.
The maximum possible friction force between two surfaces before sliding begins is the product of the coefficient of static friction and the normal force: Fmax = μsN. It is important to realize that when sliding is not occurring, the friction force can have any value from zero up to Fmax. Any force smaller than Fmax attempting to slide one surface over the other will be opposed by a frictional force of equal magnitude and opposite direction. Any force larger than Fmax will overcome friction and cause sliding to occur.
When one surface is sliding over the other, the friction force between them is always the same, and is given by the product of the coefficient of kinetic friction and the normal force: F = μkN. The coefficient of static friction is larger than the coefficient of kinetic friction: it takes more force to make surfaces start sliding over each other than it does to keep them sliding once started.
These empirical relationships are only approximations: they do not hold exactly. For example, the friction between surfaces sliding over each other may depend to some extent on the contact area, or on the sliding velocity. The friction force is electromagnetic in origin: atoms of one surface "stick" to atoms of the other briefly before snapping apart, causing atomic vibrations, and thus transforming the work needed to maintain the sliding into heat. However, despite the complexity of the fundamental physics behind friction, the relationships are accurate enough to be useful in many applications.
2006-08-12 04:42:48 · answer #1 · answered by Dean C 2 · 2⤊ 0⤋
The coefficient of friction (also known as the frictional coefficient) is a dimensionless scalar value which describes the ratio of the force of friction between two bodies and the force pressing them together. The coefficient of friction depends on the materials used -- for example, ice on metal has a low coefficient of friction (they slide past each other easily), while rubber on pavement has a high coefficient of friction (they do not slide past each other easily). Coefficients of friction need not be less than 1 - under good conditions, a tire on concrete may have a coefficient of friction of 1.7. Magnetically attractive surfaces can have very large friction coefficients, and glued or welded together surfaces have infinite friction coefficients.
For more see :
http://en.wikipedia.org/wiki/Friction
2006-08-12 11:37:08 · answer #2 · answered by fred 055 4 · 0⤊ 0⤋
in addition to the almost perfect answer of DeanC:
If the motion is tumbling (trundling), for example, a hard ball rolling over more deformable surface. Then, the kinetic coefficient of this new type of friction is:
µr = M / N with units of (meters).
N – the normal force; M – the momentum of N
µr depends on the elastic properties of the surface and has a clear geometrical interpretation due to unequal deformations in the front and the back of the rolling sphere.
2006-08-12 13:22:00 · answer #3 · answered by kaned 2 · 0⤊ 0⤋
One thig that should be added: The coefficient of motional friction is usually much lower than the coefficient of static friction.
Doug
2006-08-12 11:50:34 · answer #4 · answered by doug_donaghue 7 · 0⤊ 0⤋
It is dimensionless. It basically tells you the magnitude of the amount of friction you can expect when you multiply it by a normal force component.
2006-08-12 14:17:28 · answer #5 · answered by ObliqueShock_Aerospace_Eng 2 · 0⤊ 0⤋
no unit.
It describes the surface's tendency to cause friction. A slippery surface will have a lower value than a rigid, rugged one.
2006-08-12 11:38:52 · answer #6 · answered by D Gyroscope 2 · 0⤊ 0⤋
there are no units for the coefficent of friction.
2006-08-12 11:35:22 · answer #7 · answered by sportsmess 3 · 0⤊ 1⤋
http://en.wikipedia.org/wiki/Coefficient_of_friction
2006-08-12 11:37:59 · answer #8 · answered by weegleajeems 2 · 0⤊ 0⤋
its different for different surfaces.
2006-08-13 07:46:14 · answer #9 · answered by babloo 3 · 0⤊ 1⤋
I'll think about it.
2006-08-12 12:02:36 · answer #10 · answered by Ahab 5 · 0⤊ 3⤋