Cavendish Experiment

Performed in 1897, the Cavendish Experiment aimed to determine the value of G, the universal gravitational constant. Cavendish constructed an apparatus (shown in the figure) where suspended masses would be attracted to another set of masses by gravity. This attraction created a torsion (twisting) in the suspending wire which was painstakingly measured to find the value of G. This experiment took place around a century after Newton’s original publication.

Visualization of Cavendish experiment. The two yellow spheres with masses depicted by small letter m are placed on opposite sides of a metal stick which is suspended in the air by the wire. On the wire above the stick, a small mirror is placed. Right below the wire, a wooden stick is placed with two red spheres with masses depicted by capital M. The spheres are placed on the opposite sides of a wooden stick, next to the yellow masses. The blue tube with a light source is shining on the mirror, which reflects the light onto a scale placed next to the system.

Figure 1: Cavendish used an apparatus similar to this to measure the gravitational attraction between two spheres (m) suspended from a wire and two stationary spheres (M). Setup: 1: wire, 2: mirror, 3: pivot, 4: light source, 5: scale. The setup on the image consists of a wire, number 1, a mirror, number 2, a pivot, number 3, a light source, number 4, and a scale, number 5 Image source : OpenStax