Work Done (SQA National 5 Physics): Revision Note

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

• When work is done, energy is transferred

• Work done is equal to the amount of energy transferred

• If a force acts in the same direction as the object's movement, then the object gains energy

• If a force acts in the opposite direction to the object's movement, then the object loses energy

Work done pushing a box

Calculating work done

• The relationship between work done, force, and distance is:

• Where:

  • = work done, or energy transferred, measured in joules (J) or newton-metres (N m)

    • 

  • = force applied, measured in newtons (N)

  • = distance in metres (m)

Relationship triangle for work done, force and distance

• Using relationship triangles is covered in more detail in the revision note on motion relationships

Examples of work done

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

  • 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 is done

• 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