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.

Work is done when a force causes displacement in the direction of the force.

1. Suma is swimming in a pond – Work is done, as Suma applies force with her arms and legs to move forward, causing displacement.
2. A donkey is carrying a load on its back – No work is done by the donkey on the load in physics terms because the force (upward) and displacement (horizontal) are perpendicular.
3. A windmill is lifting water from a well – Work is done, as the windmill applies force to lift the water upward, causing displacement in the same direction.
4. A green plant is carrying out photosynthesis – No mechanical work is done, as there’s no displacement due to an applied mechanical force.
5. An engine is pulling a train – Work is done, as the engine exerts a force in the direction of the train’s motion, causing displacement.
6. Food grains are getting dried in the sun – No work is done in mechanical terms, as there is no force causing displacement.
7. A sailboat is moving due to wind energy – Work is done, as the wind applies force on the sails and moves the boat, causing displacement in the direction of force.