Cavendish experiment to determine G
Cavendish Balance Model
This is a simple model of a Cavendish balance. The large spheres can be moved and the small spheres comprise a torsion pendulum.
G can be determined using Cavendish torsion balance.
Two small lead balls, each of mass m1, are attached to the two ends of a bar of length l. The bar is suspected of using a fine wire. Let two large lead balls of masses m2 each is kept at a distance from the small balls. The force of attraction between m1 and m2 is 
.
The wire gets twisted under the gravitational force of attraction between the spheres. Let θ be the angle of twist of the wire and C the torque per unit twist. (Refer to below figure).
