What is mu in physics?

Hint:The ratio of the frictional force resisting motion of two surfaces in contact to the normal force pressing the two surfaces together is known as the coefficient of friction. The Greek letter mu $\left( \mu \right)$ is usually used to represent it. Friction is developed when one surface is in contact with the other. It can be defined as a force that will be retarding an object from moving.

Complete step-by-step solution:
1.Friction is created when one surface rubs against another. It's a force that can stop an object from moving.
2. The Greek letter "mu" $\left( \mu \right)$ is assigned to the coefficient of friction, and it is unit less. The normal force on an object is multiplied by the friction force.
3.The Newton is the unit of friction (N). For static friction and kinetic friction, the coefficient of friction has different values.
4.The frictional force resists the force applied to an object in static friction, and the object remains at rest until the static friction force is overcome. The frictional force resists an object's motion in kinetic friction.
The frictional force can be written as,
$\vec{f}=\mu \vec{N}$
The forces acting on a block is shown below,

Note: Friction is the force that opposes motion between any two surfaces that come into contact with one another. Static, sliding, rolling, and fluid friction are the four types of friction. Solid surfaces experience static, sliding, and rolling friction. The normal force is the force exerted by surfaces to keep solid objects from passing through them. A contact force is a normal force. If the surfaces of a table and a box are not in contact, they cannot exert normal forces on each other.