Cavendishexperimentet

The Cavendish experiment, also known as the Cavendish torsion balance, was conducted by Henry Cavendish in 1798–1799 to measure the force of gravity between masses and thereby determine the gravitational constant G. It provided the first precise experimental value for G and enabled a calculation of Earth’s mean density.

The apparatus consisted of a horizontal rod with two small lead balls at its ends, suspended from a fine torsion wire. Two larger lead balls were placed nearby on a frame to attract the small balls. The gravitational attraction caused a tiny twist in the suspending wire. The angle of twist was measured optically, typically by reflecting light from a small mirror mounted on the rod onto a scale. From the measured torque and the known geometry and masses, Cavendish derived G.

To ensure that the measured force reflected gravity rather than spurious interactions, Cavendish took care to minimize electrostatic, magnetic, and air-current effects and to control environmental factors. The experiment was performed with great care to isolate the gravitational signal and to calibrate the apparatus.

The result for G obtained by Cavendish was about 6.75 × 10^-11 N m^2/kg^2, within roughly one percent of the modern accepted value. This measurement allowed, for the first time, a determination of Earth’s mass using Newton’s law of gravitation and demonstrated that G could be determined experimentally.

The Cavendish experiment is regarded as a landmark in experimental physics. Its torsion-balance approach influenced subsequent measurements of gravity and remains a fundamental reference in discussions of experimental gravitation.