Short Title

Determining 'Big G'


gravitational constant, torsion balance, Cavendish experiment

Subject Area

Physics, Laboratory

Type of Submission



The force of attraction between any two objects in the universe is related to the mass of each object and the distance between the objects multiplied by a proportionality factor, G. We measure the universal gravitational constant using a torsion balance with two pairs of metal masses, one small and one large. Attaching a mirror to the pendulum bob and using a laser projected from the mirror allows us to measure the angular twist of the torsion ribbon in response to the attraction between the large and small masses on either side of the pendulum. We used three different methods of using the pendulum to calculate this constant. Each of the three methods yielded values of G: GI = 6.41 ± 0.05 x 10-11, GII = 6.36 ± 0.04 x 10-11, and GIII = 7.8 ± 0.1 x 10-11.