When a material is elongated in a given axial direction there will be some corresponding elongation in the transverse direction. The ratio of lateral to axial [[Strain|strain]] is referred to as Poisson’s ratio, $\nu$, and is a property dependent on the material. $\nu=-\dfrac{d\varepsilon_{transverse}}{d\varepsilon_{axial}}$ ![[poisson.png|center|400]]