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Calculating Changes in Energy

Physics: AQA GCSE Higher, topic 1.1.7

Calculating Changes in Energy

Energy can be stored in many different ways and the amount of energy stored can be calculated using the following equations:

Kinetic energy

Kinetic energy

  • Kinetic energy is the energy stored by an object's movement.
  • The equation for calculating kinetic energy stored is:
  • Kinetic energy = 1/2 × mass × velocity2
  • Ek = 1/2mv2
Units

Units

  • Kinetic energy is measured in joules (J).
  • Mass is measured in kilograms (kg).
  • Velocity is measured in metres per second (m/s).
Gravitational potential energy

Gravitational potential energy

  • Gravitational potential energy is the energy stored in objects raised above the Earth’s surface.
  • This energy exists because of the Earth’s gravitational field.
  • The equation for calculating gravitational potential energy stored is:
  • Change in gravitational potential energy = mass × gravitational field strength × change in height
  • ΔEp = mgΔh
Units

Units

  • Gravitational potential energy is measured in joules (J).
  • Mass is measured in kilograms (kg).
  • Gravitational field strength is measured in Newtons per kilogram (N\kg).
  • Height is measured in metres (m).
Elastic potential energy

Elastic potential energy

  • Elastic potential energy is the energy stored when an object is being stretched, compressed or squashed.
  • The equation for calculating elastic potential energy stored is:
  • Ee = 1/2ke2
  • Elastic potential energy = 1/2 × spring constant × extension2
Units

Units

  • Elastic potential energy is measured in joules (J).
  • The spring constant is measured in Newtons per metre (N/m).
  • Extension is measured in metres (m).

Test yourself on Calculating Changes in Energy

  • What is the equation for calculating kinetic energy?

  • An elastic band has a spring constant of 3 N/m and is extended by 20 cm. What is the elastic potential energy stored in the spring?

  • An elastic band has a spring constant of 6 N/m and is extended by 1.5 m. What is the elastic potential energy stored in the spring?

  • An elastic band has a spring constant of 20 N/m and is extended by 0.5 m. What is the elastic potential energy stored in the spring?

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