Work Done (Edexcel IGCSE Physics: Double Science)

• 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 doesn’t result in any movement, no work is done

• When work is done on an object, energy is transferred
• The amount of energy transferred (in joules) is equal to the work done (also in joules)

energy transferred (J) = work done (J)

Work is done when a force is used to move an object

• If a force acts in the direction that an object is moving, then the object will gain energy (usually to its kinetic energy store)
• If the force acts in the opposite direction to the movement then the object will lose energy (dissipated to the surroundings usually by heating)

Examples of Work

• Work is done on a ball when it is lifted to a height 
  • The energy is transferred mechanically from the ball's kinetic energy store to its gravitational potential energy store

The weight on the ball produced by the gravitational field does work on the ball over a distance 

• Work is done when a bird flies through the air
  • The bird must travel against air resistance, therefore energy is transferred from the bird's kinetic store to its thermal store and dissipated to the thermal store of the surroundings

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

• The amount of work that is done is related to the size of the force and the distance moved by the object in the direction of the force
• To calculate the amount of work done on an object by a force the following formula is used

W = f × d

• Where:
  • W = work done in joules (J) or newton-metres (N m)
  • F = force in newtons (N)
  • d = distance in metres (m)

• This equation can be rearranged with the help of a formula triangle:

Work, force, distance formula triangle