This Demonstration shows the relative transverse strain resulting from a specified axial strain, as described by Poisson's ratio, defined as the negative ratio of transverse strain to axial strain. Tensile strain is considered positive, while compressive strain is considered negative. The definition contains a minus sign so that normal materials have a positive ratio. The value of Poisson's ratio varies from material to material. However, in isotropic materials, Poisson ratios can fall anywhere between the theoretical limits of and . In this Demonstration, you can assign two different values of Poisson's ratio to bars of two different materials (the red and the green cylinders) and observe how these materials respond to the same axial strain. The blue cylinder is a reference representative of an undeformed bar not subject to any strain.