Strain
Fractional deformation under load.
Formula
Variables
Example
1 mm over 1 m = 0.001
How it works
Strain measures how much a material stretches or compresses compared with its original length. It is defined as the change in length divided by the starting length, so it gives a unitless ratio that lets you compare deformation in objects of different sizes. The formula works because the same absolute change means very different things for short and long pieces, and strain captures that relative effect.
When to use it
Use this formula when checking how much a beam, rod, wire, or structural member deforms under a load. It is common in materials testing, civil engineering, and mechanics whenever you need a size-independent measure of deformation.
Worked example, step by step
A steel bar is 2.5 m long before loading. After the load is applied, it lengthens by 2.0 mm. Convert the change in length to metres: 2.0 mm = 0.0020 m Use the formula: ε = ΔL / L0 Substitute the values: ε = 0.0020 / 2.5 Calculate: ε = 0.0008 Final answer: the strain is 0.0008 (or 8 × 10^-4)
Common mistakes to avoid
- Using the final length instead of the original length in the denominator
- Forgetting to convert units so ΔL and L0 are in the same units
- Giving strain units even though it is a dimensionless ratio
Did You Know?
Strain is dimensionless.
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