Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: THURSDAY, September 9, 1993 TAG: 9309080090
SECTION: EXTRA PAGE: 1 EDITION: METRO
SOURCE: Joel Achenbach
DATELINE: LENGTH: Long
Veronica W. of Lynchburg, Va., asks, "Why do mosquitos become attracted to one individual and ignore others?"
Dear Veronica: It may have something to do with carbon dioxide. (Oh, that again.) Mosquitoes are definitely attracted to CO2. As you know, animals give off carbon dioxide in their breath, which is one reason why some types of mosquitoes love to hover around your head at night and drive you crazy. CO2 is also released from your skin, along with numerous other chemical secretions, like lactic acid, that may attract mosquitoes.
So do some people exude more CO2 than others? More lactic acid and other 'skeeter delights? We can't tell you. There's not much funding for research in that area, says entomologist Ronald Ward, a mosquito expert at the Walter Reed Army Institute of Research in Washington. But he says he'd like to find out.
In the meantime, we advise you to remain calm, even serene, when mosquitoes are biting; they'll naturally drift away from you, toward the person who is slapping and cursing and breathing hard and emitting lots of CO2. nn
Janet C., of Baltimore, asks, "Would you be weightless at the center of the Earth?"
Dear Janet: Sure would. With the planet's mass equally distributed around you, gravity would be canceled out.
If you're a major gravity aficionado, you may find this answer perplexing. On the one hand it would feel as though you were in outer space. On the other hand, you would be in the center of a huge mass-an object that bends, distorts, curves the very fabric of space-time. Why shouldn't you feel something?
The answer is, you only feel gravity when you are accelerating toward the center of the mass. If you have two leaves floating on the surface of a pond, they each create a dimple in the skin of the water. If they get close enough, the dimples will overlap just enough to make the leaves "fall" toward one another - it looks as though they are supernaturally attracted - and clump together. But once they've fallen together, they just sit there - the tugging sensation is gone. So it is that at the center of the Earth you're not tugged in any direction. Space and time may be curved around you -gravity is the acceleration we experience when we are curve-surfing-but you're in a nice little flat spot.
It's so embarrassingly simple-this column should be renamed "Highlights For Children."
David T. of Denver writes, "Everyone knows what happens when you put a bottle filled with water in the freezer-the water expands, turning to ice, and breaks the bottle. OK, what would happen if you filled a very strong safe with water and dropped the temp below freezing? What if the safe was too strong for the freezing water to bulge out the walls of the safe? Would it be able to freeze at all?"
Dear David: The water would not freeze, at least not right away. You'd just have very cold liquid water.
The reason is elementary: As pressure rises, the freezing temperature drops. Inside the chilling safe, some ice crystals do form, increasing the pressure and keeping the remaining water in a liquid state. That remaining water will freeze if you can get the safe colder, down to about minus-20 degrees Celsius, according to physicist Robin Blumberg Selinger of the University of Maryland. And then the solid ice, being under great pressure, will be denser than the stuff you have in your freezer. (Ice is not all the same.)
You can see this phenomenon illustrated by putting a beer in the freezer. The beer is under pressure. Pull it out when it is still liquid, pop the top off, and-if it's cold enough-it will freeze up in a few seconds.
We hate it when that happens.
Speaking of temperature, Vasu J. of Washington says we were wrong when we wrote recently that atoms would stop moving entirely at "absolute zero." This letter gives you an idea of the kind of mail we receive daily. He writes, "Since the third law of thermodynamics states that absolute zero of temperature cannot be attained in a finite number of steps, an experiment to determine motion at absolute zero cannot be performed.
"Assuming, for the sake of argument, that absolute zero is achieved theoretically, then quantum mechanics dictates that even at absolute zero an atom possesses a residual amount of energy called `zero-point energy.' The zero-point energy, which is never zero, is related to Heisenberg's Uncertainty Principle. If atoms stopped moving `entirely' then their location in space would be known with complete precision in violation of the Uncertainty Principle . . . "
Dear Vasu: No no no, it just felt like absolute zero because of the wind chill factor.
Russell S., of Raton, N.M., asks, "Why do we think domesticated horses, such as race horses, have to have iron shoes? Horses have existed in the wild for centuries without the services of a farrier."
Dear Russell: Those wild horses also didn't have people on their backs shouting, "Giddyup!" The shoeing of horses is directly a function of our insistence on riding them.
by CNB