Question

Define coefficient of frictional force. What are its unit?

Answer 1

A coefficient of a friction is a value that shows the relationship between the force of friction between two objects and the normal reaction between the objects that are involved.  It has no units.

Answer 2

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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.