Gravitational Potential Energy (Edexcel IGCSE Physics)

Revision Note

Leander Oates

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Gravitational potential energy

  • 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:

G P E space equals space m space cross times space g space cross times space h

  • 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

gpe man, IGCSE & GCSE Physics revision notes

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

Gravitational field strength diagram, downloadable AS & A Level Physics revision notes

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

GPE graphs, downloadable AS & A Level Physics revision notes

Graphs showing the linear relationship between GPE and height

Worked Example

A man of mass 70 kg climbs a flight of stairs that is 3 m higher than the floor.

Gravitational field strength is approximately 10 N/kg.

Calculate the increase in energy transferred to his gravitational potential store.

Answer: 

Step 1: List the known quantities

  • Mass of the man, m = 70 kg

  • Gravitational field strength, g = 10 N/kg

  • Height, h = 3 m

Step 2: Write down the gravitational potential energy equation

G P E space equals space m space cross times space g space cross times space h 

Step 3: Calculate the gravitational potential energy

G P E space equals space 70 space cross times space 10 space cross times space 3

G P E space equals space 2100 space straight J

Estimating Physical Quantities, downloadable AS & A Level Physics revision notes

 

Examiner Tips and Tricks

When doing calculations involving gravitational field strength, g, don't panic, you will always be told the value of g in your equation sheet in your exam!

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Leander Oates

Author: Leander Oates

Expertise: Physics

Leander graduated with First-class honours in Science and Education from Sheffield Hallam University. She won the prestigious Lord Robert Winston Solomon Lipson Prize in recognition of her dedication to science and teaching excellence. After teaching and tutoring both science and maths students, Leander now brings this passion for helping young people reach their potential to her work at SME.