Fun fact of the day

Most people assume that metal tends to stay cooler than other objects in a room. For instance, touch the nearest piece of metal to you. For me, it’s on my chair. It feels cold compared to my hand. Now if I touch my desk, which is made out of some cheap composite material, I notice what feels like a clear difference in temperature. Assuming my laptop hasn’t warmed my desk, though, there is no difference. The reason has to do with specific heat capacity.

Specific heat capacity refers to the amount of energy it takes to raise an object’s temperature by a particular amount. For instance, at room temperature, it takes 4.187 joules to raise a kilogram of water by 1 degree (Kelvin). (I remember that number well from my days in a physics class. Why the professor let us round the acceleration due to gravity to 10, but not the specific heat capacity of water to 4.2, I don’t know.) This number, however, will change depending upon what we’re measuring. Metals, for example, tend to be very low. Aluminum is only .897. Copper is .385. This is why your pots and pans heat up so quickly on the stove or why the zipper on your pants is so much hotter than everything else when you finish your laundry.

Going back to that piece of metal near you. If you were so inclined and had the right thermometer, you could be quick to find that it’s the same temperature as the rest of the room. So is any other random object you see that isn’t a light bulb, TV, laptop, etc. The reason why it feels cold is because you’re probably much warmer than the air around you, so when you touch it, the heat from your hand is quickly sapped up. Heat is transferred to metals more quickly than it is to most other common objects.

(Incidentally, this is why ocean temperatures are so important to global warming. It takes a long time to heat up and cool down water. The fact that we’re seeing the swings we are means there is a lot of energy going into the seas.)

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2 Responses

  1. The reason has to do with specific heat capacity.

    Are you sure that it isn’t more a matter of conductivity, at least for metal?

  2. Practically speaking, you can thaw frozen food far quicker by putting it on an aluminum (or other metal) pan. Throwing frozen food in the ocean should usually work also, though I don’t recommend it.

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