Apparatus for analysing the torsional behaviour of metal wires according to Coulomb (1784)

In 1784, the French military engineer Charles Augustin Coulomb published the results of experiments in which he had investigated the torsion of metal threads. For this purpose, he used a wooden stand with a crossbar into which a thin metal thread could be clamped. A lead cylinder (either 245g or 979g) was attached to the lower end of the thread, with a pointer attached to its underside that hovered just above a scale resting on the wooden plate.

The cylinder was twisted and released; it then performed rotational oscillations. Coulomb determined the period for 20 oscillations. By varying parameters such as the length of the thread, the diameter of the thread or the attached mass in a defined way, Coulomb was able to demonstrate that the torsional force in metal threads (within the limits of elasticity) is inversely proportional to the length as well as proportional to the fourth power of the diameter.

further reading

Coulomb, C.A.: Recherches théoriques et expérimentales sur la force de torsion, et sur l'élasticité des fils de métal. In: Memoires de l'Academie Royale des Sciences pour l'année 1784, Paris 1787, 229 – 269

Heering, P. (2006). Regular Twists: Replicating Coulomb's Wire-Torsion Experiments. Physics in perspective, 8, 52-63.