In the movie "A Christmas Story," it's a triple-dog-dare that prompts Flick to taste a freezing-cold flagpole on a winter's day in Indiana. When he can't get his tongue unstuck, Ralphie's friend is rescued by the local fire department, while his classmates watch from the school windows.
Wet fingers can stick to metal, too, but tongues are especially vulnerable. The tongue is naturally moist, and its surface is riddled with tiny fissures, where water can collect. When you touch your tongue to metal whose temperature is below the freezing point of water (32 degrees), the water on its surface freezes solid, forming an icy bond between you and the metal.
Chemist Francis DiSalvo of Cornell University says that ice forms so quickly because metals are so good at conducting heat. Touch your tongue to a frozen rubber pencil eraser, and you can't make it stick. That's because the thermal conductivity of rubber is about 100 times lower than that of metal. Cold rubber just can't remove enough heat from the water on your tongue to freeze it.
But metals have high thermal conductivity, quickly siphoning off heat from water and lowering its temperature to freezing. In an instant, you're (painfully) attached to a frigid flagpole. The remedy for unsticking: a glass of warm water, poured over the tongue to melt the ice.
If freezing the tongue hurts, burning it is no picnic, either. And hot pizza is often the culprit in tongue and roof-of-the mouth burns. According to physicist Jearl Walker, of Cleveland State University, whether a food burns the mouth depends on more than just its temperature.
Spill a cup of hot chocolate into your lap, and you may get a real burn. Walker notes that clothing soaks up and holds onto hot liquid, keeping it in contact with the skin long enough to cause a burn. But sip the same drink, and only a tiny amount of hot liquid touches the mouth - and for a very brief time. Sipping breaks the liquid into droplets, which carry little thermal energy individually. Taking sips also mixes air into the liquid, he says, cooling it. The result: Little thermal energy is transferred from the drink to your mouth. And you're less likely to be burned.
But hot pizza can mean a world of (mouth) hurt. In fact, Walker says, all foods with hot cheese should be approached with dining caution. While the cheesy surface may feel lukewarm, the mass of cheese underneath can be a hotbed of thermal energy. Once the hapless pizza-eater has bitten off a glob of surprisingly hot cheese, he may find it clinging to the roof of his mouth or tongue, downloading its thermal energy in a painful burst. Ouch.
For cooling relief, try sipping a cold drink. Or search for the flagpole scene from "A Christmas Story" at youtube.com.