AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Changes in energy: g . p . e . = mass × gravitational f ield strength × height
Gravitational potential energy (g.p.e.) is the energy stored in an object because of its position in a gravitational field.
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Gravitational potential energy (g.p.e.) is the energy stored in an object because of its position in a gravitational field. You calculate it by multiplying three quantities: the object's mass in kilograms, the gravitational field strength in newtons per kilogram, and the vertical height in metres. For example, lifting a 2 kg book 1.5 m on Earth, where g = 9.8 N/kg, gives g.p.e. = 2 × 9.8 × 1.5 = 29.4 J. The height must be the vertical change, not the distance moved along a slope. Doubling any one factor doubles the energy stored. This relationship lets you compare energy transfers when objects are raised or lowered, and it links to kinetic energy and conservation of energy.
What earns the marks
- State that gravitational potential energy depends on mass, gravitational field strength and vertical height.
- Substitute values into g.p.e. = mass × gravitational field strength × height with correct units: kg, N/kg and m.
- Calculate the energy in joules, including correct use of g = 9.8 N/kg on Earth unless told otherwise.
- Recognise that height means vertical height change, not distance along a slope.
- Rearrange the equation to find mass, gravitational field strength or height when the other values are known.
- Explain that doubling mass or height doubles the gravitational potential energy stored.
Common mistakes and how to put them right
Using the distance along a slope instead of the vertical height.
Put it right by resolving or measuring the vertical height change.
Forgetting to convert grams to kilograms or centimetres to metres.
Put it right by converting all values to kg and m before substituting.
Using g = 10 N/kg when the question specifies 9.8 N/kg.
Put it right by using the value given in the question.
Exam tips
- Write the equation, substitute the values with units, then calculate and give the unit J.
- Check that height is vertical and measured in metres before substituting.
- If the question asks for height or mass, rearrange the equation carefully before putting numbers in.
Try the lesson
The start of the Changes in energy: g . p . e . = mass × gravitational f ield strength × height lesson, made from checked teaching notes for this specification point.
Have a go first
A book of mass 2 kg is lifted 3 m onto a shelf. The gravitational field strength is 9.8 N/kg. Calculate the gravitational potential energy gained by the book.
Listen
Gravitational potential energy (g.p.e.) is the energy stored in an object because of its position in a gravitational field. You calculate it by multiplying three quantities: the object's mass in kilograms, the gravitational field strength in newtons per kilogram, and the vertical height in metres. For example, lifting a 2 kg book 1.5 m on Earth, where g = 9.8 N/kg, gives g.p.e. = 2 × 9.8 × 1.5 = 29.4 J. The height must be the vertical change, not the distance moved along a slope. Doubling any one factor doubles the energy stored. This relationship lets you compare energy transfers when objects are raised or lowered, and it links to kinetic energy and conservation of energy. A strong answer earns marks for these points. State that gravitational potential energy depends on mass, gravitational field strength and vertical height. Substitute values into g.p.e. = mass × gravitational field strength × height with correct units: kg, N/kg and m. Calculate the energy in joules, including correct use of g = 9.8 N/kg on Earth unless told otherwise. Recognise that height means vertical height change, not distance along a slope. A common slip: Using the distance along a slope instead of the vertical height. Instead, resolving or measuring the vertical height change. Exam tip: Write the equation, substitute the values with units, then calculate and give the unit J.
Key words
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Gravitational potential energy
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Gravitational field strength
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Vertical height
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Conservation of energy
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See every definition
- Gravitational potential energy
- The energy stored in an object because of its position in a gravitational field.
- Gravitational field strength
- A quantity in newtons per kilogram that is multiplied by mass and vertical height to calculate gravitational potential energy.
- Vertical height
- The vertical change in position, not the distance moved along a slope, measured in metres.
- Conservation of energy
- A principle to which the relationship for gravitational potential energy links, alongside kinetic energy.
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