Elasticity & Young's Modulus
Stretch materials, see stress-strain. Builds on Hooke's Law & Springs.
You hang a 10 kg weight from a 1-meter steel wire (cross-section 1 mm²). The wire stretches by 0.5 mm. Now you replace the wire with one that has DOUBLE the cross-sectional area (2 mm²) but the same length and material.
How much does the thicker wire stretch?
Half the stretch! Double the area means half the stress, which means half the strain. It's 0.25 mm.
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Pull on different materials and watch the stress-strain curve build. Notice the linear region, the yield point, and the break!
σ = E · ε (F/A = E · ΔL/L)
Each material has its own stiffness E. Steel is 20,000× stiffer than rubber.
Steel cables must stretch slightly under load — engineers use E to calculate exact deflection
Bone has E ≈ 15 GPa — strong enough to support your body, flexible enough to absorb impacts
Different materials and thicknesses give different tension and tone — all governed by Young's modulus
“Every material has a personality: how much it stretches, when it yields, and when it breaks.”
Materials Tester
Pull on different materials and watch them deform. Compare stress-strain curves for steel, aluminum, rubber, and glass.
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Pull rubber until it's 5× its length — notice it springs back! Now try glass — it snaps with almost no deformation. Which stores more energy before breaking?
The area under the stress-strain curve is the energy absorbed before failure. Rubber absorbs enormous energy; glass absorbs almost none (brittle failure).