We talked about the Coriolis effect, and said it was important in large weather patterns, causing low pressure areas to rotate counterclockwise in the northern hemisphere and clockwise in the southern hemisphere.
There is a persistent myth that water going down the drain will be different in different hemispheres. However, this is not true, because the drain isn’t big enough. And remember how we used throwing a tennis ball as an example, but then said you can’t really see the Coriolis effect while playing catch? What if you threw something very far, like a missile? Well, then the Coriolis effect does become important, and a missile specialist has to think about that when aiming.
The Rossby number (abbreviated Ro) is a dimensionless number that tells you whether the Coriolis effect is important in a situation or not. U is the velocity, L is the length (distance something is moving), and f involves the latitude and speed the Earth spins. If the number is very large, then the Coriolis effect is unimportant. (High speeds and short distances make Ro large.) This is the case in your bathtub, playing catch, and in tornadoes.
If the Rossby number is small, however, then the Coriolis effect is important, as in cyclones and long-range artillery. (Low speeds and long distances make Ro small.)