Torsional Pendulum

"Life is what happens to you while you're busy making other plans"
John Lennon - Beautiful Boy (1980)

A torsional pendulum consists of a disk (or some other object) suspended from a wire, which is then twisted and released, resulting in an oscillatory motion. The oscillatory motion is caused by a restoring torque which is proportional to the angular displacement,

I is the rotational inertia of the disk about the twisting axis, k (kappa) is the torsional constant (equivalent to the spring constant). This equation is exactly the same as SHM we have already discussed. By direct comparison the period of the torsional pendulum is given by,

Similar to the simple pendulum, so long as the angular displacement is small (which means the motion is SHM) the period is independent of the displacement. Torsional pendulums are also used as a time keeping devices , as in for example, the mechanical wristwatch .

Copernicus' parents: Copernicus, young man, when are you going to come to terms with the fact that the world does not revolve around you?!

Dr. C. L. Davis
Physics Department
University of Louisville
email: c.l.davis@louisville.edu