AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Forces and elasticity: extension, e, in metres, m
Extension is the increase in length of an elastic object when a stretching force acts on it.
Checked against the AQA 8464 specification (opens in a new tab) on .
- Point 9 of 19
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Extension is the increase in length of an elastic object when a stretching force acts on it. It is measured in metres, symbol m, and given the symbol e in equations such as force = spring constant × extension. To find e, measure the stretched length and subtract the original unstretched length: e = L − L₀. For example, a spring of original length 0.12 m stretched to 0.20 m has e = 0.20 m − 0.12 m = 0.08 m. Extension is not the same as total length, and it must be expressed in metres before substitution into an equation. A negative value would indicate compression rather than extension.
What earns the marks
- Defines extension as the increase in length of an elastic object when a stretching force is applied.
- States that extension is measured in metres, symbol m, and is represented by the symbol e.
- Shows the method e = stretched length − original length, using consistent units.
- Distinguishes extension from total length, recognising that total length includes the original length.
- Converts a length given in centimetres or millimetres to metres before using it in an equation.
- Interprets a negative extension value as compression rather than stretching.
Common mistakes and how to put them right
Using the total stretched length as the extension.
Put it right by subtracting the original length, e = L − L₀.
Substituting centimetres directly into an equation that requires metres.
Put it right by dividing by 100 to convert cm to m.
Confusing the symbol e with energy or with the base of natural logarithms.
Put it right by checking the context, since in elasticity e stands for extension in metres.
Exam tips
- Write the word equation first, then substitute values with units, so the examiner can see that extension is a difference between two lengths.
- Check that every length in a calculation is in metres before substituting; convert cm or mm first.
- If a question gives total length and original length, calculate e before using force = spring constant × extension.
Try the lesson
The start of the Forces and elasticity: extension, e, in metres, m lesson, made from checked teaching notes for this specification point.
Have a go first
A spring has a natural length of 12 cm. A student hangs a mass on the spring and measures its new length as 17 cm. What is the extension of the spring in metres?
Listen
Extension is the increase in length of an elastic object when a stretching force acts on it. It is measured in metres, symbol m, and given the symbol e in equations such as force = spring constant × extension. To find e, measure the stretched length and subtract the original unstretched length: e = L − L₀. For example, a spring of original length 0.12 m stretched to 0.20 m has e = 0.20 m − 0.12 m = 0.08 m. Extension is not the same as total length, and it must be expressed in metres before substitution into an equation. A negative value would indicate compression rather than extension. A strong answer earns marks for these points. Defines extension as the increase in length of an elastic object when a stretching force is applied. States that extension is measured in metres, symbol m, and is represented by the symbol e. Shows the method e = stretched length − original length, using consistent units. Distinguishes extension from total length, recognising that total length includes the original length. A common slip: Using the total stretched length as the extension. Instead, subtracting the original length, e = L − L₀. Exam tip: Write the word equation first, then substitute values with units, so the examiner can see that extension is a difference between two lengths.
See it
Key words
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Extension
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Measurement and units
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Practical measurement skills
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See every definition
- Extension
- The increase in length of an elastic object when a stretching force acts on it, measured in metres, symbol m, and represented by the symbol e.
- Measurement and units
- Extension must be expressed in metres before substitution into an equation, and a length given in centimetres or millimetres is converted to metres first.
- Practical measurement skills
- To find e, measure the stretched length and subtract the original unstretched length, using consistent units.
Label the diagram
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