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Why is water so cool? Ask your local physicist

SHARE Why is water so cool? Ask your local physicist

If the last couple of thermometer-busting days are any indication, Utahns will be hankering for a glass of ice water or a jump into the pool or a run through the sprinklers more than usual this summer.

Water, literally, is cool. Vital, in fact. That plain, boring, ubiquitous substance that covers more than 70 percent of Earth's surface is your savior from the heat. Shut down your sweat glands and your body temperature — fueled by your metabolism — immediately starts to climb. Soon you reach the danger level and before you know it you've keeled over from heat stroke, and they're dragging you out feet first.

But what is it, exactly, about water that cools us down? When we sweat, for example, "you would think it wouldn't do any good at all because the stuff coming out of your body is the same temperature," said Charles Torre, a Utah State University physics professor. As for taking a cold drink, it gives you a fleeting cooling sensation but "it's like putting a small ice cube in a big pot of hot soup," said University of Utah medical school professor Matthew Movsesian. "It really doesn't do much."

Answer: It's all about heat transfer. When you drink your ice water, you smack your lips and say ahhh as the liquid flows down your gullet, but that's just the beginning. The water makes its way through the stomach, into the gut and then into the bloodstream, which carries it around to your extremities and dumps it, whereupon sweat glands pick it up and pump it out onto your skin.

But here's the cool part (giggle).

Air has a high vapor pressure, which means that air — especially warm air — likes to turn any water it encounters into a gas and absorb it. That innocent drop of sweat on your arm wants to go into the atmosphere, but in order to turn into a gas it has to absorb a lot of heat. And where does it get that heat?

Why, from you. "Literally, it's just robbing the heat from your body," Torre said.

Kids, of course, don't stop with sweating — they'll turn on the sprinklers or jump in the pool, since they instinctively know that even water that's been sitting around for a while is almost always cooler than your skin.

When that cool water contacts you, it absorbs your heat in an attempt to equalize the temperatures between skin and liquid (what scientists call equilibrium.) More than almost any other substance, water is usually cooler than its surroundings because it has a tendency to absorb vast amounts of heat without getting hot itself.

"That's one advantage of having so much water on our planet," said U. chemistry professor Jerry Driscoll. "It soaks up a lot of heat and doesn't give it up easily. Moon temperatures soar — they fluctuate all over the place — because they don't have that moderating effect." So, stay off the moon if you want to stay cool.

Of course, not everyone takes advantage of water's unique properties. Bountiful resident Evonne Reid has a pool and every summer it's just one kid after another jumping in and cooling off and messing around — but adults are a different story.

"They're afraid of what they look like in a swimming suit," she said. "They'd rather suffer."

E-mail: aedwards@desnews.com