Stress
Internal force per unit cross-sectional area.
Formula
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Example
1000 N over 0.01 m² = 100 kPa
How it works
Stress tells you how concentrated a force is over a material's cross-sectional area. The same force can be harmless on a large area but very large on a small one, which is why stress is defined as force divided by area. This idea helps compare how hard different parts of a component are being loaded, regardless of their size.
When to use it
Use this formula when a load is acting on a material and you want to know how much internal force each unit area must carry. It is common in engineering, mechanics, and materials science for beams, rods, bolts, cables, and structural members.
Worked example, step by step
A steel rod carries a tensile force of 5000 N. Its cross-sectional area is 0.0025 m². Use σ = F / A. σ = 5000 / 0.0025 σ = 2,000,000 Pa σ = 2.0 MPa
Common mistakes to avoid
- Using the length of the object instead of the cross-sectional area
- Forgetting to convert units so force is in newtons and area is in square metres
- Confusing stress with strain, which measures deformation rather than force per area
Did You Know?
Stress determines whether a material will fail under load.
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