An object of mass m is moving on a rough surface in the rightward direction. Work done by the friction on the object is:

CONCEPT:

• Work is said to be done by a force when the body is displaced actually through some distance in the direction of the applied force.
  • The capacity for doing work done is called energy.
• Since the body is being displaced in the direction of F, therefore work done by the force in displacing the body through a distance s is given by:

\(W = \vec F \cdot \vec s\)

Or, W = Fs cos θ

• Thus work done by a force is equal to the scalar or dot product of the force and the displacement of the body.
• Static Frictional Force is applied to the body when it is at rest is known as static friction.
• Friction acting on a body in motion, to resist the motion is called Kinetic Frictional Force.

EXPLANATION:

When an object is moving on a Rough surface Kinetic Frictional forces tries to resist the Movement.

• Here, the frictional force is opposite to the applied force and hence, is opposite to the displacement. Therefore the angle between the frictional force and displacement is 180°.

W = Fs cos 180° = Fs cos (90° + 90°)

W = - Fs sin 90° = -Fs

Work done by a frictional force is Negative.