Scientific concept of work:
- To understand the way we view work and define work from the point of view of science, let us consider some situations:
- Push a pebble lying on a surface. The pebble moves through a distance. You exerted a force on the pebble and the pebble got displaced. In this situation work is done.
- A girl pulls a trolley and the trolley moves through a distance. The girl has exerted a force on the trolley 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.
A closer look at the above situations reveals that two conditions need to be satisfied for work to be done:
(i) a force should act on an object, and
(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.
Can there be displacement of an object in the absence of any force acting on it? Think. Discuss this question with your friends and teacher.
Look at the activities listed below. Reason out whether or not work is done in the light of your understanding of the term ‘work’.
- Suma is swimming in a pond.
- A donkey is carrying a load on its back.
- A wind mill is lifting water from a well.
- A green plant is carrying out photosynthesis.
- An engine is pulling a train.
- Food grains are getting dried in the sun.
- A sailboat is moving due to wind energy.
A person of mass 50 kg climbs a tower of height 72 metres. Calculate the work done. (g = 9.8 m s−2).