Because gravity holds planets in orbit and makes falling objects land with a bang, we tend to think of it as a powerful force, but it isn’t really. It is only powerful in a kind of collective sense, when one massive object, like the Sun, holds onto another massive object, like the Earth. At an elemental level gravity is extraordinarily unrobust. Each time you pick up a book from a table or a coin from the floor you effortlessly overcome the gravitational exertion of an entire planet. What Cavendish was trying to do was measure gravity at this extremely featherweight level.
