if all motion is relative, how do we know the Earth isn’t stationary with everything else in the Universe rotating around us, albeit in a right weird and in uniform way.

Question

if all motion is relative, how do we know the Earth isn’t stationary with everything else in the Universe rotating around us, albeit in a right weird and in uniform way.

In: Physics

Answer 1

Only motion in a straight line, with no acceleration, is relative. Rotation involves acceleration and so is *not* relative, but absolute. On earth we can tell that the earth is rotating on its axis by swinging a large pendulum, like they do in some museums, and see that the pendulum’s swing rotates over several hours. Gyro-compasses use the same principle.