In our day to day lives, we frequently use the word ‘work’ to describe activities we do in the course of the day. Doing your homework, folding clothes, making a presentation on the computer, all these are considered as work in everyday language.
However, in Physics, work does not constitute any of these activities. In Physics, when force is applied on an object, due to which the object undergoes movement from its original place, only then do we say that work is done.
Thus, we can say that, ‘work is said to be done when a force is applied on an object and the object gets displaced under the influence of that force’.
Conditions under which work is said to be done-
Work is said to be done only when the following three conditions are met-
- A force is applied on the object
- There is a displacement in the position of the object, or there is a change in the shape or size of the object.
- The displacement or change is as a result of the force applied.
Conditions under which no work is done-
There is no work done in the following conditions-
- There is no force applied- such as when you’re lying on the couch and reading a book. Since no force is applied here, work done is zero
- There is no displacement, even if force has been applied- for example, when you push a heavy box with all your strength and it does not move. Here, you’re applying force, but there is no displacement. Hence, work done is said to be zero.
- There is application of force, there is also displacement of the object, but the object comes back to its original position- for example, if you push a trolley around a circular park, and come back to your original place after completing one round of the park. Here, you apply a pushing force on the trolley, due to which the trolley moves. However, net displacement is zero, since the trolley is back where it started. Hence, work done is said to be zero.
- If the force applied is at right angles to the displacement of the object. When the direction of the force applied, and the displacement of the object are at 90 degrees to each other, work done is said to be zero.
How is work measured?
Since work is a physical quantity that depends upon force applied and net displacement, we can say that ‘the amount of work done is equal to the product of the force applied on an object, and the displacement of that object as a result of that force.
Work = Force x Displacement
W = F x s
Unit Of Work-
The SI unit of work is newton-metre. Its symbol is Nm. A newton-metre is also called a joule. Its symbol is J
Thus, 1 joule of work is said to be done when a force of 1 newton causes a displacement of 1 metre in an object, in the direction of the applied force.
There is also a larger unit of work, called as kilojoule. Its symbol is kJ.
Properties of work-
- The greater the magnitude of the force applied, greater is the work done.
- The greater the displacement in an object, greater is the work done.
- If either the force applied or the magnitude of displacement changes, then work done will also change.