Work Done (CIE IGCSE Physics: Co-ordinated Sciences (Double Award))

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

• When work is done, energy is transferred
• Work done and energy transferred are equivalent quantities

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

Work done equation

• The formula for work done is:

 

• Where:
  • = work done, measured in newton-metres (N m)
  • = force applied, measured in newtons (N)
  • = distance in metres (m)
  • = energy transferred, measured in joules (J)

Formula triangle for work done, force and distance

To use a formula triangle, simply cover up the quantity you wish calculate and the structure of the equation is revealed

• Using formula triangles is covered in more detail in the revision note on Speed & velocity

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

• Therefore:

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 in done

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
  • 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