How Mass of the Earth Can be Measured?
The mass of the earth was first calculated from an experiment done by Cavendish in 1797-98. Newton knew that the gravitational acceleration at the earth’s surface was: g = G M / r^2 So the earth’s mass is: M = gr^2 / G The gravitational acceleration, g, is well known and easy to measure by dropping a rock or something. The radius of the earth, r, can be found in various ways. The missing piece in the puzzle is the constant of proportionality in Newton’s law of gravitation–G. This was first measured by Cavendish who used a torsion scale to measure the attractive force between two masses in his laboratory. This famous experiment to measure G is sometimes called “weighing the earth” because by calculating G you allow the calculation of the earth’s mass (and the mass of every other astronomical body).
