What is the coefficient of static friction?
The force of static friction can be calculated by taking the coefficient of friction between the two surfaces and multiplying it by the normal force that the surface is applying to the object. On a flat surface, the normal force is equal to the force of gravity acting down on the object.
The coefficient of kinetic friction is the force between two objects when one object is moving, or if two objects are moving against one another. The coefficient of friction is dimensionless, meaning it does not have any units. It is a scalar, meaning the direction of the force does not affect the physical quantity.
- Measuring μ An easy way to measure the coefficient of static friction is to place two objects together and then tilt them until the top one slides. The angle at which one object starts to slip on the other is directly related to the coefficient. When the two objects are horizontal there is no frictional force.
- There are four types of friction: static, sliding, rolling, and fluid friction. Static, sliding, and rolling friction occur between solid surfaces. Static friction is strongest, followed by sliding friction, and then rolling friction, which is weakest. Fluid friction occurs in fluids, which are liquids or gases.
- This constant ratio is called the coefficient of friction and is usually symbolized by the Greek letter mu (μ). Mathematically, μ = F/L. Because both friction and load are measured in units of force (such as pounds or newtons), the coefficient of friction is dimensionless.
The Coefficient of friction is defined as the ratio of force of friction to the normal force, μ = F / N . Consider the following two Figures. Fk = Force of kinetic friction, μk = coefficient of kinetic friction, N = Normal force or the force perpendicular to the contacting surfaces.
- It must be overcome to start moving the object. Once an object is in motion, it experiences kinetic friction. If a small amount of force is applied to an object, the static friction has an equal magnitude in the opposite direction. The maximum force of static friction is μs times the normal force on an object.
- Kinetic friction is a force that acts between moving surfaces. An object that is being moved over a surface will experience a force in the opposite direction as its movement. The magnitude of the force depends on the coefficient of kinetic friction between the two kinds of material.
- angle of internal friction. It is the angle (φ), measured between the normal force (N) and resultant force (R), that is attained when failure just occurs in response to a shearing stress (S). Its tangent (S/N) is the coefficient of sliding friction. Its value is determined experimentally.
Sliding friction, kinetic friction or moving friction, is the force that is required to keep two surfaces moving relative to each other. The magnitude of this force depends on only two factors for non-microscopic situations: the coefficient of sliding friction between the two materials and the normal force.
- Sliding is a type of frictional motion between two surfaces in contact. This can be contrasted to rolling motion. Both types of motion may occur in bearings. The relative motion or tendency toward such motion between two surfaces is resisted by friction.
- The coefficient of kinetic friction is the force between two objects when one object is moving, or if two objects are moving against one another. The coefficient of friction is dimensionless, meaning it does not have any units. It is a scalar, meaning the direction of the force does not affect the physical quantity.
- σ is the standard deviation for a population, which is the same as “s” for the sample. μ is the mean for the population, which is the same as XBar in the sample. In other words, to find the coefficient of variation, divide the standard deviation by the mean and multiply by 100.
Updated: 16th October 2019