Day 2 Question 3: An attempt to explain the Coriolis force

Question 3:

Recently a lecturer in physical geography attempted to explain the Coriolis force. He appealed to the experience of being on a merry-go-round and attempting to walk from its center to the edge. "This is difficult to do because of the Coriolis force." Discuss this explanation.

Apparently this instructor needs a basic course in physics. The reason that it is difficult to walk from the center to the edge of a rotating carousel is centrifugal force. The Coriolis “effect”, on the other hand, is not an actual force, but an effect of your frame of reference. A better analogy to explain the Coriolis effect would be to imagine sitting on one end of the carousel, not knowing that it was rotating, and trying to throw a ball to your friend sitting directly across the center from you. This assumes, of course, that the center of the carousel is as empty as the aforementioned instructor’s head, allowing you a clear shot at your friend. The ball leaves your hand, traveling directly toward where your friend was when you released the ball. As the ball is traveling in the air, however, your friend is rotating away from where the ball eventually lands. To an observer situated in the rotating frame of reference, it appears that ball has curved away from its original path. To an observer watching from above, in a fixed frame of reference, the ball traveled in a straight line. If the merry-go-round is rotating counter-clockwise as seen from above, analogous to the Earth’s rotation as seen from above the North pole, the ball would appear to always veer to the right in the perspective of the thrower. This apparent curving of the trajectory seems to be caused by some unseen force. This apparent force is named for the French scientist Gaspard Coriolis who first described it. It is referred to by some as the Coriolis force, but technically it is more proper to call it the Coriolis effect, since it is not an actual force.

On the rotating Earth, the Coriolis effect depends on the distance traveled and the distance from the Equator. The Coriolis effect is weakest at the equator, strongest at the poles, and it is only significant over large distances. Accordingly, it is humorous that a gift shop which straddles the equator in Kenya advertises that the toilets on the north end of the store flush the opposite direction as those on the south end. This phenomenon is caused solely by the design of the toilets, which dictates the direction that every toilet flushes, and not the Coriolis effect, which (1) does not matter over the small diameter of a toilet bowl, and (2) is ineffective so close to the equator!