Range of poissons ratio I know the range of poisson's ratio is -1 to 0.5 but how do you arrive at this expression? I am a 11th grade student and I am not too familiar with advanced physics
 A: The answer is a bit lengthy, but can be arrived at using arguments about elastic strain energy. Here is a very detailed explanation:
Limits of Poisson's ratio in isotropic solid
This was written at a graduate mechanical engineering level, so I'll simplify it here.
Imagine that there exists a function $\psi$ that describes how much energy is contained in a solid per unit volume. This quantity is a function of material properties and deformation. For a linear elastic, isotropic solid, the material properties are Young's modulus (E), and the Poisson ratio ($\nu$).
One of the assumptions of the theory of elasticity is that the elastic energy $\psi$ is a function that is strictly increasing for all conceivable deformations. The details of this assumption are in my other answer (the link), but it turns out that $\nu$ can only be in the interval
$$
-1 < \nu < \frac{1}{2}
$$
I hope this clears up your question at an appropriate level. Let me know in the comments if not!
A: Poisson's ratio can be expressed in terms of Young's modulus $E$, Bulk modulus $K$ and Shear modulus $G$. I hope you know how do arrive at these relationships;
$$ G=\frac{E}{2(1+\nu)}$$
$$ K=\frac{E}{3(1-2\nu)}$$
$E, K$ and $G$ and all NOT less than zero.
From the equation of $G$ you can see that it's the value of $v=-1$ which would make the denominator $0$ and $G$ very large. That's the limit for $G$.
And from the equation of $K$ it's the value of $v=0.5$ that makes the denominator $0$ and $K$ very large. The limit for $K$.
Therefore $v$ can only fall between $-1$ and $0.5$.
