HOW COME? Why carpet is toasty, tile chilly

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My grandchildren and I have a question: How come a tile floor feels much colder to the touch than a carpet or rug in the same room? asks reader Robert Reh.

Try the doorway test: One bare foot planted on your bedroom carpet, the other resting (gingerly) on the bathroom tile floor. Even if both rooms are at the same 72-degree F. temperature, your bedroom foot will feel warmish, your bathroom foot downright frosty.

However, our skin isn't the most accurate thermometer. Get three bowls. Fill one with very warm water, one with cold water, and the third with water at room temperature. Put your left hand in the hot water, your right in the cold, for about 10 seconds. Then quickly plunge both hands into the room-temp bowl.

The result? Your preheated left hand will inform you that the water is uncomfortably cool. Your chilled right hand will proclaim that the water is in fact toasty warm.

How come? Whether we perceive an object or substance to be cooler or warmer depends on how heat flows between it and our bodies. Heat and temperature are related, but they're actually two different things. Temperature measures the average amount molecules are moving in an object or substance (the molecules' average kinetic energy). Heat measures the amount of energy transferred between objects at different temperatures.

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Heat energy flows in one direction, from a higher-temperature object to one at a lower temperature. As the energetic molecules in the hotter object make contact with the more sluggish molecules in the cooler one, energy gets transferred. So pour boiling water into a room-temperature coffee mug, and the mug warms, even as the water loses energy and cools.

Your body's temperature hovers around 98 degrees F. Touch a coffee table, and heat energy flows from your warm fingertips into the 72-degree F. wood. Result: The temperature in your fingertips drops slightly, and your skin senses coolness. Grab a mug of hot coffee, and heat energy flows from the cup into your hand. And you sense warmth.

But as it turns out, not all objects are equally good at transferring heat. Carpet fibers transfer heat slowly, and so our skin stays warmer. Tiles are a better heat conductor, quicker at siphoning energy from the soles of our bare feet. Which is why, at the same room temperature, tiles feel colder than carpet.

Still, if you think tile feels chilly, try stepping into an empty cast-iron tub. Metal is an especially good conductor. Your tootsie thermometer may decide the tub is even colder than the ceramic tiles around it.

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