Work

WORK:

What is work?

There is a difference in the term ‘work’ in day-to-day life and it in science. To make this point clear let us consider an example .You climb up the steps of a staircase and reach the second floor of a building just to see outside from there.  If we apply the scientific concept these activities involve a lot of work.

Scientific Concept of Work??

Let us consider some situations-

Rema pulls a box and the box moves through a distance. The girl has exerted a force on the box and it is displaced. Therefore, work is done. Lift a book through a height. To do this you must apply a force. The book rises up. There is a force applied on the book and the book has moved. Hence, work is done.

The two conditions need to be satisfied for work to be done:

(i) A force should act on an object,

(ii) The object must be displaced. If any one of the above conditions does not exist, work is not done. This is the way we view work in science.

Definition of work:

  • The product of the force applied on an object and displacement caused due to the applied force in the direction of the force.
  • Work is a scalar quantity. It has no direction of its own but a magnitude.
  • Work done = Force * Displacement
  • SI unit of Work: N-m or J (Joule)
  • 1 Joule is the amount of work done on an object when a force of 1 N displaces it by 1 m along the line of action of the force.

Nature of Work Done:

 

 1. Positive Work: If a force displaces the object in its direction, then the work done is positive. The example of this kind of work done is motion of ball falling towards ground where displacement of ball is in the direction of force of gravity.

 

2. Negative Work: If the force and the displacement are in opposite directions, then the work is said to be negative. For example if a ball is thrown in upwards direction, its displacement would be in upwards direction but the force due to earth’s gravity is in the downward direction.

 

3. Zero Work: If the directions of force and the displacement are perpendicular to each other, the work done by the force on the object is zero.

For example, when we push hard against a wall, the force we are exerting on the wall does no work, because in this case the displacement of the wall is d = 0. However, in this process, our muscles are using our internal energy and as a result we get tired.