What Is Poissons Ratio?
Poisson’s ratio deals with the way stretching or compressing an object in one direction causes it to compress or stretch in the other direction. The ratio measures the extent of this effect in a particular substance. This can vary considerably, and the ratio can even be negative, usually in man-made substances. The technical definition of Poisson’s ratio is “the ratio of transverse contraction strain to longitudinal expansion strain.” This sounds complicated, but describes a fairly simple effect. To picture it, imagine a piece of rubber, such as that used in a rubber band. When you stretch the band, it becomes both narrower and longer. The relationship between these two changes is what’s measured by Poisson’s ratio. In reality, Poisson’s ratio applies in three dimensions. In the rubber band example, the thickness of the stretched band also decreases – it’s just harder to see. To picture the effect in three dimensions, imagine taking a pet toy in the shape of a cube and squeezing two op
