# Regarding spring constant.

by A Dhingra
Tags: constant, spring
 PF Gold P: 943 I assume you have in mind a helical spring. The main process involved in stretching such a spring is twisting the wire of which it is made. The torque needed to twist the wire through a given angle is proportional to r4 in which r is the radius of the wire, and is also proportional to the rigidity modulus, n, of the wire. Provided the turns of the spring remain almost at right angles to the longitudinal axis of the spring, then the spring constant is given approximately by $$k = \frac{\pi r^4 n}{2 a^2 L}$$ in which $a$ is the radius of a turn of the spring and $L$ is the length of the wire from which the spring is made.