Straight lines that don't stay straight.

This uses the standard small-deflection approximation for horizontal motion, y ≈ Ω sinφ × d²⁄v (equivalent to Ω sinφ × vt² with flight time t = d⁄v), the same one used in classical Coriolis-force derivations for artillery. It only holds while the sideways drift stays small compared with the distance travelled — true for everything on the picker above, but not true for hurricanes or ocean gyres, where the deflection isn't a small correction to an otherwise-straight path, it's the entire reason the path curves into a spiral. Those need full rotating-fluid dynamics (geostrophic balance), not this formula — which is why they're mentioned here rather than added as a fifth button. No, you can't see this in your bathtub: the Wikipedia article above documents the long-running myth directly. At bathtub scale the number above comes out smaller than a human hair, while ordinary basin asymmetry and the leftover swirl from filling the tub are enormously larger — the effect only becomes the dominant swirl-setting force in a laboratory-grade setup: a large, perfectly symmetric, still tank left to settle for roughly a day. The hero animation's disc spins many thousands of times faster than the real Earth so the curve is visible in a few seconds; Earth's own version of this is real but far too slow to watch.