Big G, little g

摘要

You might think that Earth's huge gravity would be a boon to those wishing to measure big C, Newton's gravitational constant. Quite the reverse, for one simple reason: it is difficult to work out our planet1 s exact mass. Without this crucial number, it is impossible to calculate big C from Newton's inverse square law, which relates the force of gravity between a test mass, the mass of the Earth and the distance between them.