Gravitational Potential Energy (Edexcel IGCSE Physics)

• Energy in the gravitational potential store of an object is defined as:

The energy an object has due to its height in a gravitational field

• This means:
  • If an object is lifted up, energy will be transferred to its gravitational store 
  • If an object falls, energy will be transferred away from its gravitational store 

The gravitational potential energy equation

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

• Where:
  • GPE = 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)

The gravitational potential energy equation applied to a person lifting a mass

Energy is transferred to the mass's gravitational store as it is lifted above the ground

Gravitational field strength

• The gravitational field strength (g) on the Earth is approximately 10 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

Some values for g on the different objects in the Solar System

• The two graphs below show how GPE changes with height for a ball being thrown up in the air and when falling down

Graphs showing the linear relationship between GPE and height