Work Done (Cambridge (CIE) IGCSE Physics): Revision Note

Work done & energy transfers

• Mechanical work is done when an object is moved over a distance by a force applied in the direction of its displacement

  • It is said that the force does work on the object

  • If a force is applied to an object but does not result in any movement, no work is done

• When work is done, energy is transferred

• Work done and energy transferred are equivalent quantities

Work is done when a force is used to move an object over a distance, and energy is transferred from the person to the box

Work done equation

• The formula for work done is:

$W=Fd=∆E$

• Where:

  • $W$ = work done, measured in joules (J)

  • $F$ = force applied, measured in newtons (N)

  • $d$ = distance moved in the direction of the force, measured in metres (m)

  • $∆E$ = energy transferred, measured in joules (J)

• Mechanical work done and electrical work done are equivalent to energy transferred

$\mathrm{work}\mathrm{done}=\mathrm{energy}\mathrm{transferred}$

• Work done can also have units of newton-metres since:

$1\mathrm{N}\mathrm{m}=1\mathrm{J}$

Examples of work done

• Work is done on a ball when it is lifted to a height: 

  • A force is required to lift the ball

  • Work is done against the weight force to lift the ball through the gravitational field

  • Energy is transferred as work done

Work done lifting a ball

Work is done against the ball's weight as it is lifted, transferring energy to its gravitational potential store 

• Work is done when a bird flies through the air

  • A force is required to overcome the drag force

  • Work is done against the drag force as the bird flies over a distance

  • Energy is transferred as work is done

Work done by a bird

The bird does work against air resistance (drag) as it flies through the air