Chapter 6 Friction focuses on another type of force, known as frictional force. It stops objects from sliding over one another. The electromagnetic forces between two bodies in contact act between the charged particles present on their surfaces. Thus, each body experiences a force of contact..
The direction of the force of contact acting on a particular body is not necessarily perpendicular to the contact surface. However, it can be resolved into two components, one perpendicular to the contact surface and the other parallel.
The perpendicular component of frictional force is called the normal contact force or normal force; the parallel component is called friction. It can be divided into types, namely, static and kinetic frictional force.
Frictional forces can act between two bodies that are not sliding over each other but are in contact. The friction produced in such cases is called static friction. The direction in which static friction acts so that the total force acting on the body keeps it at rest with respect to the body in contact. There exists a law of friction.
If the bodies slip with respect to each other, the force of friction is given by
fk = µkN Here, N is the normal contact force, and µk is the coefficient of kinetic friction between the bodies.
The direction in which kinetic friction acts on a body is the opposite of its velocity with respect to the body applying the force of friction. The frictional force fk or fs is independent of the area of contact as long as the normal force N is constant. Laboratory methods like the Horizontal Table Method and the Inclined Table Method can measure the coefficient of friction.