Spiral springs are used to provide a restoring torque to an oscillating shaft when it rotates through an angular displacement. They exhibit similar stiffness characteristics to linear springs, except that the effect is one of torque rather than force. The stiffness of a spiral spring depends on its physical dimensions and the rigidity of the steel strip from which it is formed. The student can easily calculate the theoretical simple harmonic motion of the spring, and compare the value with simple experimental results. A range of moments of inertia of the oscillating part is provided.
The wall mounted unit consists of a spiral spring coiled from a length of 25 x 0.6mm steel strip to give an effective length of 2 metres, attached to a shaft mounted in ball bearings. A cord carrying a weight hanger is wound round the shaft, and a load applied to twist the spring. Spring deflection is measured with an attached 360° scale.
A cord and weight hanger are supplied. A set of discs which can be attached to the shaft change the frequency of oscillation, measured by the stop watch provided.