Q: Why are water towers bigger on the top than the bottom? Wouldn't that make them unbalanced?

-Jade D.

A: If it's an unfamiliar sight, the large bulbous shape of a water tower looming over a small Midwestern town might at first look like an alien spacecraft. The shaft descending from its center, though, is not a tractor beam sucking up unsuspecting passersby. It is instead the sturdy column of what is known as a single pedestal elevated water tower.

Water supplies are elevated so that gravity can help the water travel through pipes and into people's homes. In communities without a nearby hill, building a tower is the next best option.

"Water towers are designed to make the most efficient use of materials to hold the most water at the needed elevation, or sometimes for aesthetic reasons, or both," says John E. Durrant.* A narrow supporting column allows engineers to maximize the height (to take advantage of gravity) while using as little material as possible (to save money). Rather than being unbalanced, the tank is perfectly balanced on the center column, with its full weight pushing down to the earth. And they look pretty cool, even if they're not from outer space.

- Andy

* John E. Dumtnt is Managing Director of Engineering Programs for the American Society of Civil Engineers.

Q: How can a sneeze travel at about 100 miles per hour without breaking the wall when I sneeze at it? Why doesn't the sneeze make my arm flail violently away from my mouth when I sneeze at it?

- Gabriel S., age 6, Pennsylvania

A: Its true that the speed of a sneeze is nothing to, er, sneeze at. Though there's no "standard sneeze unit," most people probably sneeze at roughly 1 00 miles per hour - about the same rate as a professional pitcher's fastball. But (fortunately for the wall and your arm) even a mighty sneeze's momentum is puny. Momentum, which determines how hard it is to stop a moving object, depends not only on speed, but also on the mass of an object. Unless you're a giant with a mighty head cold, whatever comes out of your nose is pretty light stuff.

"If something has a small enough mass, like a drop of water, it can move very fast without hurting because it doesn't have much momentum," explains Julien Clinton Sprott.* "So sneeze away without fearing for the wall or your arm!"

- Ruth

*Julien Clinton Sprott is a professor of physics at the University of Wisconsin-Madison.

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