Pearson Edexcel · GCSE · Physics
Course version: 1PH0 · Version from Sept 2016
Recall and use the equation to calculate the change in gravitational PE…
Full specification wording
Topic 8 – Energy – forces doing work: 8.8 Recall and use the equation to calculate the change in gravitational PE when an object is raised above the ground: change in gravitational potential energy (joule, J) = mass (kilogram, kg) × gravitational field strength (newton per kilogram, N/kg) × change in vertical height (metre, m) h g m GPE ∆ × × = ∆
This equation gives the energy transferred to an object's gravitational store when it is lifted.
Checked against the Pearson Edexcel 1PH0 specification (opens in a new tab) on .
- Point 8 of 15
Study notes
From the checked teaching notes for this specification point.
The idea
This equation gives the energy transferred to an object's gravitational store when it is lifted. Multiply the mass in kilograms by the gravitational field strength in newtons per kilogram by the change in vertical height in metres: ΔGPE = m × g × Δh. Near the Earth's surface g is about 9.8 N/kg, often rounded to 10 N/kg. Lifting a 2 kg box by 3 m gives ΔGPE = 2 × 10 × 3 = 60 J. Only the vertical change in height counts, so a load carried along a level floor gains no gravitational potential energy. Keep every quantity in its stated unit before multiplying, and remember the result is in joules.
What earns the marks
- Multiplies mass in kilograms by gravitational field strength in newtons per kilogram by the change in vertical height in metres.
- Uses only the vertical component of the height change when the object moves along a slope or a level path.
- States the answer in joules and keeps the mass, field strength and height in their stated units before multiplying.
- Applies a gravitational field strength of about 9.8 N/kg, or the rounded value of 10 N/kg, consistently within a calculation.
Common mistakes and how to put them right
Uses the total distance travelled instead of the vertical height change.
Put it right: Measure only the rise above the ground.
Adds the three quantities rather than multiplying them.
Put it right: Multiply mass, field strength and height together.
Forgets to convert grams to kilograms or centimetres to metres.
Put it right: Convert to kg and m before substituting.
Treats a horizontal movement as a gain in gravitational potential energy.
Put it right: Recognise that a level path gives zero change in height.
Exam tips
- Write the equation first, then substitute values with their units so the joule result is clear.
- Check whether the height given is vertical; if a slope length is quoted, use the vertical rise.
- Round g to 10 N/kg only when the question allows it, and say which value you used.
Try the lesson
The start of the Topic 8 – Energy – forces doing work: 8.8 Recall and use the equation to calculate the change in gravitational PE when an object is raised above the ground: change in gravitational potential energy (joule, J) = mass (kilogram, kg) × gravitational field strength (newton per kilogram, N/kg) × change in vertical height (metre, m) h g m GPE ∆ × × = ∆ lesson, made from checked teaching notes for this specification point.
Have a go first
A 2 kg book is lifted 3 m vertically. Using g = 10 N/kg, calculate the change in gravitational potential energy of the book.
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Test your understanding of Topic 8 – Energy – forces doing work: 8.8 Recall and use the equation to calculate the change in gravitational PE when an object is raised above the ground: change in gravitational potential energy (joule, J) = mass (kilogram, kg) × gravitational field strength (newton per kilogram, N/kg) × change in vertical height (metre, m) h g m GPE ∆ × × = ∆
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