Why does metal feel colder than clothing if they are both at room temperature?
Why does metal feel colder than clothing if they are both at room temperature? asks a reader.
Have you ever climbed into a cast-iron tub before it’s filled, and touched your bare back to the metal? Even in a warm room, the tub will make you flinch. Or stepped barefoot on marble tiles after walking across a carpet? Common sense tells you that the carpet and the marble are probably at the same temperature. But your bare feet, acting as a handy thermometer, tell a different story: The marble feels much cooler.
While your skin may not be the most accurate thermometer, it is sensing a real difference between materials. It all comes down to the movement of heat between one object and another.
While heat and temperature are related, they’re actually two different things. Temperature measures the average amount molecules are moving in a substance, or their average kinetic energy. Heat is the energy a substance has because of the energy of all of its molecules. So while a mug and a bathtub full of water may be at the same temperature—say, 100 degrees F.—the big tub of water has much more stored heat.
Put two objects of different temperatures together, and heat energy will be transferred from hotter object to cooler. Pour boiling water into a room-temperature mug, and the mug warms up, even as the water loses heat energy. Eventually, both will reach the same temperature.
What does all this have to do with objects around the house that feel oddly cool (or strangely warm) to the touch? Your body, a substantial reservoir of heat energy, maintains a temperature of about 98.6 degrees F. So your own temperature is, on average, more than 20 degrees higher than that of the room air’s air and the objects in it. Making you a walking, talking oven.
As we’ve seen, heat flows from a hotter object to a cooler object. Which is why we bundle up in winter, to help the body maintain its nearly 100-degree internal temperature even in frigid 15-degree air.
So when you touch an object at 72 degrees—say, your wooden desk—you are transferring heat energy from your very warm fingertips to the cooler wood. As they gain energy, molecules in the wood begin moving more energetically. And as heat energy is transferred from your hand at the point of contact, the temperature in you fingertips drop, and your skin senses coolness. (But since your body’s metabolic furnace works hard to maintain your high temperature, you and your desk will never reach temperature equilibrium.)
Why does metal (and marble) feel extra-cool? Different materials conduct heat energy more or less easily. Metal is an especially good conductor of heat, losing and gaining heat quickly. So when you touch a metal cake pan at room temperature, heat flows swiftly from your hand into the pan. With the quicker, steeper drop in your fingertip temperature, you sense that the pan is cooler than, say, your wooden desk. Besides wood, other slow heat conductors, like carpeting and clothing, also feel warmer to the touch.
