Where does the coefficient of friction come from?

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coefficient of friction, ratio of the frictional force resisting the motion of two surfaces in contact to the normal force pressing the two surfaces together. It is usually symbolized by the Greek letter mu (μ). Mathematically, μ = F/N, where F is the frictional force and N is the normal force. Because both F and N are measured in units of force (such as newtons or pounds), the coefficient of friction is dimensionless. The coefficient of friction has different values for static friction and kinetic friction. In static friction, the frictional force resists force that is applied to an object, and the object remains at rest until the force of static friction is overcome. In kinetic friction, the frictional force resists the motion of an object. For the case of a brick sliding on a clean wooden table, the coefficient of kinetic friction is about 0.5, which implies that a force equal to half the weight of the bricks is required just to overcome friction in keeping the bricks moving along at a constant speed, and the coefficient of static friction is about 0.6. The frictional force itself is directed oppositely to the motion of the object.

A coefficient of friction is a value that shows the relationship between two objects and the normal reaction between the objects that are involved. It is a value that is sometimes used in physics to find an object's normal force or frictional force when other methods are unavailable.

The coefficient of friction is shown by F f = μ F n {\displaystyle F_{f}=\mu F_{n}\,} . In that equation, F f {\displaystyle F_{f}} is the frictional force, μ {\displaystyle \mu } is the coefficient of friction, and F n {\displaystyle F_{n}\,} is the normal force.

The coefficient μ {\displaystyle \mu } can be two different things. It is either the coefficient of static friction μ s {\displaystyle \mu _{s}} , or the coefficient of Dynamic friction μ k {\displaystyle \mu _{k}} .The coefficient of static friction is the friction force between two objects when neither of the objects is moving. The coefficient of dynamic 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 and it does not have any unit. It is a scalar, meaning the direction of the force does not affect the physical quantity.

The coefficient of friction depends on the objects that are causing friction. The value is usually between 0 and 1 but can be greater than 1. A value of 0 means there is no friction at all between the objects; such is possible with Superfluidity. All objects, otherwise, will have some friction when they touch each other. A value of 1 means the frictional force is equal to the normal force. It is a misconception that the coefficient of friction is limited to values between zero and one. A coefficient of friction that is more than one just means that the frictional force is stronger than the normal force. An object such as silicone rubber, for example, can have a coefficient of friction much greater than one.

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The friction force is the force exerted by a surface when an object moves across it - or makes an effort to move across it.

The frictional force or force of friction (static or kinetic) can be expressed as

F f = μ N {\displaystyle F_{f}=\mu N} (1)

where

F f {\displaystyle F_{f}} is the frictional force (in Newtons),

μ {\displaystyle \mu } is the static ( μ s {\displaystyle \mu _{s}} ) or kinetic ( μ k {\displaystyle \mu _{k}} ) frictional coefficient (dimensionless) and

N {\displaystyle N} is the normal force (in Newtons).

It could also be known as a friction. It is represented as (f).

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