Speaking of pendulums: https://en.m.wikipedia.org/wiki/Mach%27s_principle https://en.m.wikipedia.org/wiki/Mach%27s_principle > it... turns out that inertia ori

Speaking of pendulums: https://en.m.wikipedia.org/wiki/Mach%27s_principle https://en.m.wikipedia.org/wiki/Mach%27s_principle > it... turns out that inertia originates in a kind of interaction between bodies, quite in the sense of your considerations on Newton's pail experiment... If one rotates [a heavy shell of matter] relative to the fixed stars about an axis going through its center, a Coriolis force arises in the interior of the shell; that is, the plane of a Foucault pendulum is dragged around (with a practically unmeasurably small angular velocity). - Einstein