Question

Define coefficient of static friction.

Answer 1

Hint: In physics, Friction is a type of relative force that acts as resistance between two bodies that are in contact with each other. Or we can simply say that, when two bodies are in contact with each other there exists a contact force which opposes their relative motion.

Complete answer:
Let us first understand the concept of static frictional force. Static friction is force which keeps an object at rest. The friction experienced when a body tries to move on a surface, without actually happening any relative motion between the body and surface.

We also need to know about Normal Reaction force: A normal reaction force acts on a body when a body is in contact with the surface and it’s always perpendicular to the contact surface which is balanced by force of gravity and it’s denoted by $N$.

And the definition of coefficient of static friction states that “It’s the maximum ratio of applied force to the normal force acting on a body when no motion of the body takes place”. It’s denoted by ${\mu }_s$ and it’s given by,
${\mu }_s={\displaystyle \frac{{\overrightarrow{F}}_s}{{\overrightarrow{F}}_N}}$
Where, ${\overrightarrow{F}}_s$ is the applied force on the body and ${\overrightarrow{F}}_N$ is the normal force acting on the body.

Note:Remember, the coefficient of static friction is a unit less quantity. As it’s a ratio of two different forces, so it is also a dimensionless quantity. Sometimes, the roughness of the surface is measured by a parameter which is known as the coefficient of static friction.