Physics Uncovered on Instagram: "The ball follows a curved path and falls off the seesaw because of the Coriolis force, which appears in systems that are rotating (like the seesaw). To someone on the seesaw (a rotating reference frame), it looks like the ball is mysteriously deflected. But to an outside observer (a fixed reference frame), the ball actually moves in a straight line — it’s just that the person meant to catch it has moved because of the rotation."