While some explanations of the Coriolis effect rely on complicated equations and confusing scientific jargon, there's a simpler way to visualize it: Picture yourself at the center of a merry-go-round (symbolizing the North Pole) spinning counterclockwise. If you throw a ball straight across to a person on the opposite side (the equator), the ball will appear to veer to the right because that person's moving faster than you are.
Sometimes the Coriolis effect is called the Coriolis force. The reason is simple: In causing an object to accelerate, it appears to change the direction of that object. However, the Coriolis force isn't a typical force like a push or a pull. The effect is actually based on the observer's perspective. A force isn't really acting on the object to make it go off course; it merely appears to curve because of the Earth's movement underneath it. To a person standing outside the rotating frame of reference, the object still moves in a straight line. Since the so-called Coriolis force doesn't actually act on the object to alter its course, some people argue that it's more accurate to continue calling it the Coriolis effect. Others differentiate between the Coriolis force and other (actual) forces by categorizing it as an inertial or fictitious force.
Now that you have a better understanding of what the Coriolis effect is, you should also know what it isn't. Most importantly, it isn't some all-powerful force that affects every moving object on the planet. Real forces, like gravity, can compete with -- or even overwhelm -- the Coriolis effect. This competition is more likely to occur with smaller objects that aren't traveling very fast or very far.
Let's reconsider the merry-go-round example. Unlike the Earth, that merry-go-round makes complete rotations several times a minute. Our planet, on the other hand, merely spins around once every 24 hours -- not enough to affect a game of catch or a flushing toilet. Even tornadoes are too small to be affected by the Coriolis "force." Find out exactly why on the next page.