The invisible force that keeps a satellite "tied" to the Earth is called gravity. It is one of the fundamental forces of nature affecting every piece of matter. The strength of this force was first determined by Henry Cavendish in Cambridge, England in 1798.
Cavendish mounted two small spheres on a light rod and positioned the assembly next to a pair of massive lead balls.
He then moved the heavy balls to a new position and observed how the gravitational attraction force twisted the rod with the light spheres into a new position. From the twisting force on the rod he calculated the force of attraction and determined the Universal Gravitational Constant G.
To get a feel for the precision required in this experiment, assume that the heavy balls have a mass of 50 kg each, and the light balls have a mass of 10 grams.
#1 Calculate the force on each of the small spheres.
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