Statics: Prestress

A toy using prestressing

This model demonstrates the effect of tension in strings which makes a toy stable and upright.



Fig. 11-7: Prestressing used in a toy (Courtesy of Miss G Christian,) [11.6]

A popular toy (Fig. 11-7a) makes use of prestressing. The mechanism for the prestressing is illustrated in Fig. 11-7b and 11-7c.

Strings are threaded through the legs of the toy and attached to the base. A spring is used to push the base down and create tension in the strings to hold the toy upright and stable (Fig. 11-7b).

When the base is pushed upwards, the tension in the string is released. The sections of the legs are no longer held in place and become unstable and the toy collapses (Fig. 11-7c). When the force is released, the spring makes the base move down, the strings become taught and the toy straightens and becomes stable.