Gravitational Potential Energy (Oxford AQA IGCSE Combined Science Double Award)

Revision Note

Gravitational Potential Energy

  • An object gains energy in its gravitational potential store when it is raised vertically through a gravitational field

  • Work is done against the weight of the object, therefore energy is transferred

  • This means:

    • If an object is lifted, energy is transferred to its gravitational potential store 

    • If an object falls, energy will be transferred away from its gravitational potential store

Calculating gravitational potential energy

  • The amount of energy in an object's gravitational potential store, Ep, can be calculated using the equation:

Ep = m × g × h

  • Where:

    • Ep = gravitational potential energy, in joules (J)

    • m = mass, in kilograms (kg)

    • g = gravitational field strength in newtons per kilogram (N/kg)

    • h = height in metres (m)

Gravitational potential energy of a mass lifted through a height

Man lifting a mass, for IGCSE & GCSE Physics revision notes
The mass gains energy in its gravitational potential store as it is lifted through a height

Gravitational field strength

  • The gravitational field strength (g) on the Earth is approximately 9.8 N/kg

  • The gravitational field strength on the surface of the Moon is less than on the Earth

    • This means it would be easier to lift a mass on the Moon than on the Earth

  • The gravitational field strength on the surface of the gas giants (eg. Jupiter and Saturn) is more than on the Earth

    • This means it would be harder to lift a mass on the gas giants than on the Earth

Gravitational field strength on different bodies of the solar system

g on the Sun is 293 newtons per kilogram, g on Jupiter is 24.7 newtons per kilogram,  g on Saturn is 10.5 newtons per kilogram,  g on Uranus is 9 newtons per kilogram,  g on Mars is 3.7 newtons per kilogram,  and g on the moon is 1.7 newtons per kilogram, for IGCSE & GCSE Physics revision notes
The gravitational field strength is different on various bodies in the Solar System
  • Remember that mass is not dependent upon gravitational field strength but weight is

Worked Example

A man of mass 70 kg climbs a flight of stairs 3 m higher than the floor. Gravitational field strength is approximately 9.8 N/kg.

Calculate the energy transferred to the man's gravitational potential energy store.

Answer:

Step 1: List the known quantities

  • Mass of the man, m = 70 kg

  • Gravitational field strength, g = 9.8 N/kg

  • Height, Δh = 3 m

Step 2: Write down the equation for gravitational potential energy

ΔEP = mgΔh

Step 3: Calculate the gravitational potential energy

ΔEP = 70 × 9.8 × 3

ΔEP  = 2058 J

Examiner Tips and Tricks

You do not need to know the gravitational field strength values, even for Earth. You will be given the values if required in the exam.

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