AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Changes in energy: height, h, in metres, m
In calculations about gravitational potential energy, height is the vertical distance an object is raised or lowered, measured in metres (m).
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
In calculations about gravitational potential energy, height is the vertical distance an object is raised or lowered, measured in metres (m). It is not the distance along a slope and not the total height above sea level unless that is the reference chosen. For example, lifting a 2 kg box from the floor to a shelf 1.5 m above the floor gives h = 1.5 m, so the energy transferred to the gravitational store is about 2 × 9.8 × 1.5 = 29.4 J. If the box is moved sideways at constant height, h does not change, so no gravitational potential energy is added. Always identify the start and end heights, subtract to find the change, and convert centimetres or kilometres to metres before substituting into an equation.
What earns the marks
- Height is the vertical distance between the object's initial and final positions, measured in metres (m).
- The value used in an equation is the change in height, found by subtracting the lower height from the higher height.
- A horizontal movement at constant height gives a height change of zero, so no gravitational potential energy is transferred.
- Converting units correctly is essential: 1 cm = 0.01 m, 1 km = 1000 m, so 250 cm becomes 2.5 m.
- Height is a scalar quantity in this context; direction is not needed, only the size of the vertical change.
- When a ramp is used, the vertical height, not the length of the ramp, is the value substituted into the equation.
Common mistakes and how to put them right
Using the length of a slope instead of the vertical height.
Put it right by identifying the vertical distance between the start and end levels.
Forgetting to convert centimetres to metres.
Put it right by dividing by 100 before calculating.
Treating height above sea level as always required.
Put it right by using the change in height between the two positions in the question.
Exam tips
- Underline the words 'raised', 'lifted' or 'falls' to decide whether height increases or decreases.
- Write the height change as a subtraction, for example 1.8 m − 0.5 m = 1.3 m, before substituting values.
- Check that every length in the calculation is in metres, and show the conversion if the question gives cm or km.
Try the lesson
The start of the Changes in energy: height, h, in metres, m lesson, made from checked teaching notes for this specification point.
Have a go first
In the equation for gravitational potential energy, Ep = m × g × h, what does the symbol h represent?
Listen
In calculations about gravitational potential energy, height is the vertical distance an object is raised or lowered, measured in metres (m). It is not the distance along a slope and not the total height above sea level unless that is the reference chosen. For example, lifting a 2 kg box from the floor to a shelf 1.5 m above the floor gives h = 1.5 m, so the energy transferred to the gravitational store is about 2 × 9.8 × 1.5 = 29.4 J. If the box is moved sideways at constant height, h does not change, so no gravitational potential energy is added. Always identify the start and end heights, subtract to find the change, and convert centimetres or kilometres to metres before substituting into an equation. A strong answer earns marks for these points. Height is the vertical distance between the object's initial and final positions, measured in metres (m). The value used in an equation is the change in height, found by subtracting the lower height from the higher height. A horizontal movement at constant height gives a height change of zero, so no gravitational potential energy is transferred. Converting units correctly is essential: 1 cm = 0.01 m, 1 km = 1000 m, so 250 cm becomes 2.5 m. A common slip: Using the length of a slope instead of the vertical height. Instead, identifying the vertical distance between the start and end levels. Exam tip: Underline the words 'raised', 'lifted' or 'falls' to decide whether height increases or decreases.
Key words
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Height
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Change in height
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Converting units
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Gravitational potential energy
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See every definition
- Height
- The vertical distance an object is raised or lowered, measured in metres (m), not the distance along a slope.
- Change in height
- Found by identifying the start and end heights and subtracting the lower height from the higher height.
- Converting units
- Centimetres or kilometres must be converted to metres before substituting into an equation, for example 250 cm becomes 2.5 m.
- Gravitational potential energy
- Energy transferred to the gravitational store when an object is raised; a horizontal movement at constant height transfers none.
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