Posted on Aug 16, 2012 in Food & drink, Other stuff
I just poured scalding hot coffee into my favorite mug. I can barely touch the outside of the mug itself, but the handle stays nice and cool to the touch? What sort of magic is this?
You wake up, stumble into the kitchen, fire up the coffee maker (or French press or single-cup brewer of your choice), and in a few minutes you pour that first steaming hot cup of joe and start your morning off on the right foot by burning yourself awake by grabbing the cup itself and not the handle.
But wait — why does the handle of the coffee mug stay so much cooler than the bit that holds the coffee? Aren’t they connected? How is this possible?
To paraphrase that famous quote from The Graduate, I want to say one word to you. Just one word.
Assuming we’re talking about your typical household coffee mug and not a thermos-style travel mug, that cup you’re holding is made out of ceramic. A ceramic, as defined by the Ceramic Tile Institute of America is “an inorganic, nonmetallic solid of crystalline, partly crystalline structure, or glass that is formed from a molten mass which solidifies on cooling, or is formed and matured by the action of the heat.”
In general, ceramics crystalline structure imparts them with certain properties, according to the University of Illinois:
The first one is the answer to our question.
Ceramics are terrible conductors of heat — and while that may seem odd when you grab the outside of the cup and burn your hand, do remember that the cup is generally rather thin and in direct contact with the coffee, where the handle is much thicker and not full of the hot liquid.
In short, the heat isn’t able to transfer itself all the way into the handle from the body of the cup itself due to the heat conducting properties of the ceramic mug.
For another great example of how fantastic ceramics are at insulating from and preventing the transfer of heat, one only needs to look at the recently retired Space Shuttle fleet’s Thermal Protection System — the underside of the shuttle was lined with ceramic tiles to protect the orbiter from the blazing heat of atmospheric reentry.
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