Cavendish Gravitational Balance
Cavendish Gravitational Balance
- Demonstrates the existence of gravitational forces between masses
- Measures the Universal Gravitational Constant, G
- Verifies the Inverse Square Law for gravitational forces
This innovative apparatus, developed from the traditional Cavendish pattern, is substantially less expensive than earlier models, making the measurement of the tiny but significant Universal Gravitational Constant more accessible to students. It is precisely constructed and allows measurements of G to be made to better than 15% relative error using either the initial acceleration method or the equilibrium displacement method.
The Cavendish experiment, performed in 1797–1798 by English scientist Henry Cavendish, was the first experiment to measure the force of gravity between masses in the laboratory[1] and the first to yield accurate values for the gravitational constant.[2][3] Because of the unit conventions then in use, the gravitational constant does not appear explicitly in Cavendish’s work. Instead, the result was originally expressed as the specific gravity of the Earth,[4] or equivalently the mass of the Earth. His experiment gave the first accurate values for these geophysical constants.
The experiment was devised sometime before 1783 by geologist John Michell,[5][6] who constructed a torsion balance apparatus for it. However, Michell died in 1793 without completing the work. After his death the apparatus passed to Francis John Hyde Wollaston and then to Cavendish, who rebuilt the apparatus but kept close to Michell’s original plan. Cavendish then carried out a series of measurements with the equipment and reported his results in the Philosophical Transactions of the Royal Society in 1798.