Strain
Relative deformation of a material.
Formula
Variables
Example
A 2 m rod stretched by 1 mm has strain ε = 0.001/2 = 0.0005.
How it works
Strain measures how much an object changes length compared with its starting length, so it is a ratio rather than a length by itself. The formula b5 = 94L / L0 works because it compares the extension or compression to the original size, making the result dimensionless and easy to compare across different materials and objects. A larger strain means a bigger proportional deformation, even if the actual change in length is small.
When to use it
Use this formula when analysing how much a bar, wire, spring, or structural member stretches or shortens under load. It is common in mechanics, materials testing, and engineering design when checking whether deformation is small, safe, or within limits.
Worked example, step by step
A steel wire has an original length of 4 m and stretches by 2 mm under load. Convert the change in length to metres: 94L = 2 mm = 0.002 m Use the strain formula: b5 = 94L / L0 Substitute the values: b5 = 0.002 / 4 Calculate: b5 = 0.0005 Final answer: the strain is 0.0005 (dimensionless)
Common mistakes to avoid
- Using the final length instead of the original length in the denominator
- Forgetting to convert units so 94L and L0 are in the same units
- Writing strain with units, even though it is a ratio and has no units
Did You Know?
Strain is dimensionless — a pure ratio of how much something stretches relative to its length.
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