Cavendish Gravitational Balance Demonstration
by United Scientific

Innovatively developed from the traditional Cavendish pattern, this version is much smaller and more compact than earlier models. It is capable of taking measurements of the tiny, yet significant, Universal Gravitational Constant, and is precisely constructed to allow measurements of G to be made with better than 15% relative error when using either the initial acceleration method, or the equilibrium displacement measurement.

Consisting of a suspended central rod that supports a small mirror for the optical detection system, it features a light aluminum cross-piece with two 20g lead balls spaced 10cm apar, and a light damping vane. With a fine, 15cm long beryllium bronze torsion wire as the suspension wire, it is capable of giving the pendulum a torsional period of 590 +/- 10 seconds.

The entire apparatus is mounted onto a 25mm thick aluminum case with glass windows to eliminate draft interference, while an adjustable screw with an angle scale at the top of the housing allows the rest position of the pendulum to be centered before any attracting masses are added.

With two large, 1.5kg lead balls for attracting masses, the distance between them and the pendulum can be varied for Inverse Square Law Investigations. The base of the gravitational balance rests upon three adjustable feet, to ensure that the entire device is level.

The following items, while not included, are highly recommended for conducting experiments with the Cavendish Gravitational Balance:

-Laser pointer, scale, and windup tape for the optical lever
-Balance (2000g capacity) & vernier caliper for determining th exact mass and diameter of the lead balls
-A stop watch for timing the oscillation in the initial acceleration method