The mechanics of a simple bathtub whirlpool are very similar to a tornado's vortex.

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What Your Bathtub Can Teach You About Tornadoes

If you've ever watched a whirlpool form in your bathtub or sink while draining the water, then you've witnessed the fundamentals of a tornado at work. A drain's whirlpool, also known as a vortex, forms because of the downdraft that the drain creates in the body of water. The downward flow of the water into the drain begins to rotate, and as the rotation speeds up, a vortex forms.

Why does the water start rotating? There are many explanations, but here's one way to think about it. Imagine yourself as a particle in the water, suddenly pulled toward the suction that the drain creates. At first, you'd find yourself accelerating toward the drain. Then, quite literally, there's a twist. Because of your previous momentum and the number of other particles rushing toward the drain at the same time, chances are that you're going to be pushed off to one side of the point of suction when you arrive. That deflection sets you on a spiraling path into the point of suction, like a moth spiraling in toward a light. Once the spiral has started in one direction, it tends to influence all the other particles as they arrive. A very strong spiraling tendency is created. Eventually, there's enough spiraling energy to create a vortex.

Vortices are obviously a common phenomenon. After all, you see them in tubs and sinks all the time. Small dust devils sometimes form when winds flow over hot deserts, and wildfires have been known to produce climbing vortices of flame and ash called fire whirls. Scientists have even observed dust devils on Mars and spotted solar tornadoes whipping out from the sun.

In a tornado, the same sort of thing happens as with our bathtub example, except with air instead of water. A great deal of the Earth's wind patterns are dictated by low-pressure centers, which draw in cooler, high-pressure air from the surrounding area. This airflow pushes the low-pressure air up to higher altitudes, but then the air heats up and is pushed upward as well by all the air behind it. The air pressure inside a tornado is as much as 10 percent lower than that of the surrounding air, causing the surrounding air to rush in even faster.

H­ow do weather conditions pull the plug on atmospheric conditions? Skip to the next page to find out how tornadoes form.