Capacity to do work

The idea

An object that has the capacity to do work possesses energy; positive work done on an object gives it energy, which it can transfer by applying a force that moves another object.

Ball and wickets

A fielder throws a cricket ball and it hits the wickets, which fall. A ball lying still on the grass cannot knock them over.

What do you think the moving ball has that the still ball does not?

• The capacity to do work
• More weight
• A different colour

Follow the energy

Press Next step through the three pictures.

Energy comes from work

The ball got its energy from the work of the fielder, and then used that energy to move the wickets. The pot got its energy from the work done in raising it. An object that has the capacity to do work has energy.

An object having the capacity to do work possesses energy. When positive work is done on an object, it gains energy, which it can transfer to another object by applying a force that moves it.

Notes

Energy is the capacity to do work. Positive work on an object gives it energy, which it can transfer by moving another object.

Check yourself

An object that has the capacity to do work is said to possess…

A fielder throws a ball. Where does the ball get its energy from?

A raised flowerpot falls and damages an object below. Why could it do this?

A moving ball hits the wickets and they move. What has the ball done?

• energy — correct. Yes!
• force. A force is a push or a pull. The capacity to do work is called energy.
• displacement. Displacement is the change in position of an object. The capacity to do work is called energy.
• From the wickets it will hit. The wickets receive energy from the ball when it hits them, not the other way round.
• From the work done by the fielder in throwing it — correct. Yes!
• From the grass it was lying on. The energy comes from the work the fielder does on the ball.
• Because raising it made its mass larger. Raising a pot does not change its mass. The work done in raising it gave it energy.
• Because the object below had more energy. The pot damages the object because the pot itself has the capacity to do work.
• It gained the capacity to do work from the work done in raising it — correct. Yes!
• It transferred energy to the wickets — correct. Yes!
• It lost its mass to the wickets. Nothing is said to be lost from its mass. The ball transfers energy by applying a force that moves the wickets.
• It gained energy from the wickets. The ball applies the force and the wickets move, so the ball is the one that transfers energy.