A quick sidebar: A common misconception is that the Coriolis force has anything to do with the direction water spirals down the bathtub. While the notion is qualitatively justified, the numbers just don't add up. Experts at vector calculus can show that the acceleration due to the Coriolis force has a magnitude of 4 * pi * f * v, where f is the frequency of rotation of the earth (once per day), and v is the speed of the object in motion relative to the earth (or how fast you threw the ball on the merry-go-round, relative to where you were riding). One can quickly compute that the Coriolis acceleration has a magnitude of (0.000145) * v. That means if the water on one side of the tub is moving by a factor of just 14 hundred-thousandths faster than it is on the other side, the Coriolis force is washed out. Furthermore, if we take a meter per second as the speed of the water down the drain, then we have an acceleration of 0.000145 meters per second squared. Compare that with the gravitational acceleration, which is 9.8 meters per second squared, and we discover that the Coriolis force (at the North Pole, where it is greatest) has a magnitude which is 15 millionths that of gravity. That means that it only takes 15 millionths more water streaming down one side of the tub, compared to the other to beat the Coriolis force. Given that the water is about a centimeter deep, this means that if just 0.14 microns more water is flowing down one side of the tub, the gravitational acceleration on that tiny difference will be greater than the Coriolis force. If you're still skeptical, just move your foot around near the drain when you take a shower, and you'll see the water spiral down one way, then another.
Why, then, is the Coriolis force enough to drive hurricanes? Because hurricanes are so large that the local random velocities that would disrupt the flow of water in your tub get washed out over the 500-mile journey to the eye
