Cavendish Experiment

Introduction

The Cavendish Experiment, conducted by British scientist Henry Cavendish in 1797-98, was the first to measure the force of gravity between masses in the laboratory, and the first to yield accurate values for the gravitational constant () and the mass of the Earth.

Experiment Setup

The experiment involved a torsion balance, a horizontal bar suspended from a thin wire, with two small lead spheres attached to either end. Two larger lead spheres were positioned close to the smaller spheres. The gravitational attraction between the pairs of masses caused the torsion balance to twist, and this tiny twisting motion was measured by observing the movement of a pointer attached to the torsion balance against a scale.

Results and Implications

The gravitational constant () can be calculated from the experiment using the formula:

where is the distance between the small and large masses, is the torsional rigidity of the wire, is the period of oscillation, is the length of the torsion balance, is the angular deflection, and is the mass of the large spheres.

Using this value of , the mass of the Earth can be determined:

where is the acceleration due to gravity at the Earth’s surface and is the Earth’s radius.

Significance

The Cavendish Experiment is one of the most famous experiments in the history of physics due to its precision and its contribution to our understanding of gravitational force. The method used by Cavendish is still the basis for modern experiments to determine . Despite the development of more precise techniques and equipment, the basic principle remains the same. The Cavendish Experiment is also a great example of the ingenuity required to measure a fundamental property of nature.

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