What is friction? Explain static frictional force.

(N/A) Friction is the force that opposes the relative motion or the tendency of relative motion between two surfaces in contact.
As shown in the figure,an object is placed on a horizontal surface. The weight $(W)$ and the normal force $(N)$ balance each other. Let a horizontal force $F$ be applied to the object.
If $F$ were the only force acting on the body,even for a very small value,the object would accelerate with $a = F/m$ in the direction of the force. However,since the object remains at rest,there must be an opposing force that makes the resultant force zero.
The force acting parallel to the contact surface is called the frictional force $(f_s)$. This force comes into action when an external force is applied to the object.
As the external force $(F)$ increases,the static frictional force also increases up to a certain limit to keep the object stationary. Frictional force opposes impending motion,which is the motion that would have occurred if friction were not present.
Since the frictional force adjusts its value as the external force increases,it is called a self-adjusting force. When the object is on the verge of moving,the frictional force reaches its maximum value,called the maximum static frictional force $(f_{s,max})$.
Laws of static friction:
$(1)$ The maximum static frictional force does not depend on the area of contact between the surfaces.
$(2)$ The maximum static frictional force is proportional to the normal force $(N)$.
Therefore,$f_{s,max} \propto N$,which gives $f_{s,max} = \mu_s N$,where $\mu_s$ is the coefficient of static friction.
The value of $\mu_s$ depends on the nature of the surfaces in contact,the material,and the temperature. It is a unitless and dimensionless quantity,typically ranging from $0.01$ to $1.5$. If the object does not move,then $f_s \leq \mu_s N$.