• id: JME-08-N08
• title: Poisson's Ratio
• tags: poisson, lateral-strain, cork, rubber

Poisson's ratio ($\nu$) is the ratio of lateral strain to longitudinal strain (with a negative sign): $\nu = -\frac{\Delta d/d}{\Delta L/L}$ It is dimensionless. Theoretical range: $-1 \leq \nu \leq 0.5$. Practical range for most materials: $0.2$ to $0.5$. Key values: Rubber $\approx 0.5$ (nearly incompressible — large lateral contraction), Cork $\approx 0$ (very little lateral change — ideal for sealing bottles), Steel $\approx 0.29$, Copper $\approx 0.34$. If $\nu = 0.5$, the material is perfectly incompressible (no volume change on stretching).