The elastic potential energy stored in a spring can easily be obtained.
K is the spring constant, x the amount of length the spring is stretched or squeezed:
is the stored energy in a spring when it is unstressed; this always equals zero. So this is the formula for the potential energy in a spring:
Consider a spring with a spring constant of 30 N/m which has a lengt of 20 cm in it's equilibrium position. A force causes the spring to increase to a length of 35 cm. The potential energy stored in the spring can be calculated;
The energy stored in a torsion spring can be calculated with a similar formula:
Variable θ is the angle of twist in radians, κ is the spring constant with units of Nm/rad.
Sometimes it is called the spring's torsion coefficient or torsion elastic modulus.