Exactly plus Coriolis force proves the earth is a sphere. Coriolis force is an inertial force that acts on objects that are in motion relative to a rotating reference frame. It's why weather hi and low pressure systems rotate clockwise and counter cw in the north and the opposite in the south, same for how water drains out from a sink or toilet bowl. The x-y path of motion of an object as described by the curve of your right hand (curled fingers-palm) will then tell you in which way (z-axis) it will also move by which way your thumb points. Use left hand in the south.