Nature of Work Done
When a force acts on an object and the object actually moves in the direction of force, then the work is said to be done by the force. Work done by the force is equal to the product of the force and the displacement of the object in the direction of force.
Positive Work: Positive work means that force is parallel to displacement.
The positive work signifies that the external force favors the motion of the body.
Example: (i) When a person lifts a body from the ground, the work done by the lifting force is positive.
(ii) When a lawn roller is pulled by applying a force along the handle at an acute angle, work done by the applied force is positive.
(iii) When a spring is stretched work done by the external force is positive.
Maximum work: \({{W}_{\max }}=Force(F)\times Distance(S)\) ; when \(\cos \theta =\) maximum = 1 ; i.e., \(\theta ={{0}^{0}}\)
It means force does maximum work when angle between force and displacement is zero.
Negative Work: Negative work means that force is opposite to displacement.
The negative work signifies that the external force opposes the motion of the body.
Example: (i) When a person lifts a body from the ground, the work done by the force of gravity is negative.
(ii) When a body is made to slide over a rough surface, the work done by the frictional force is negative.
Minimum work: \({{W}_{\min }}=-Force\left( F \right)\times Distance(S)\)
When \(\cos \theta =\) minimum = -1 ; i.e., \(\theta ={{180}^{0}}\)
It means force does minimum work when angle between force and displacement is .
(iii) When a positive charge is moved towards another positive charge. The work done by electrostatic force between them is negative.