Work Done (Edexcel IGCSE Physics: Double Science)

What is work done?

• 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

Work done and energy transfer

• 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 done pushing a box

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

• 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 done

• 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

Work done on a ball

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

Work done by a bird

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

The work done equation

• The amount of work that is done is related to the magnitude 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 work done equation 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)

Work done formula triangle

Work, force, distance formula triangle

• For help with how to use formula triangles, see the revision note on Speed