You are enjoying dessert and as you bring a heaping spoonful of ice cream to your mouth your tongue becomes frozen to the silver spoon. Surprisingly your brief entrapment has as much to do with heat as it does with cold.
The most logical suspect in this mystery would be the ice cream, sitting at a temperature below freezing. Very few would suspect it is the metal spoon that is actually responsible for trapping your tongue.
And it is all because metals are great at conducting heat.
Heat causes molecules in a material to vibrate. Once a molecule is vibrating it bumps up against a neighbouring molecule causing it to vibrate as well. Metal molecules are very tightly packed together meaning this chain reaction of vibrations will pass through them very quickly.
Metal also contains large numbers of free electrons. These electrons move freely through a metal structure absorbing heat energy and passing it along quickly as it crashes and collides with atoms and other electrons.
If a metal spoon is placed in a hot cup of tea, the molecules in the end of the spoon below the water level have more thermal energy than the ones at the cold end. Those ‘hot’ molecules bounce around, setting in motion ‘colder’ ones until that heat has been transferred up the length of the spoon.
Among metals silver is the best conductor of heat and lead is poorest. Of the more common metals, copper and aluminum have the highest thermal conductivity while steel and bronze have the least.
Back to that delicious ice cream. When your tongue makes contact with a cold spoon the metal in the spoon is conducting heat from your tongue. As your tongue cools it alerts your body that it needs to send warmth that way in the form of blood and heat energy. The spoon absorbs that heat as well, literally drawing the warmth from your tongue faster than your body can provide it. As a result, the liquid saliva on your tongue freezes, forming a bond between the spoon and your tongue.
In fact any part of your body that touches metal that is below body temperature will feel cold to the touch. Alternately hot metal will quickly transfer its heat to bare skin.
Wood, plastic, and rubber are not good heat conductors. In fact wood is 150 times less conductive than stainless steel.
As poor conductors of heat, a wood or plastic spoon is a far better choice if you want to avoid the perils of ‘sticky’ spoons. They won’t cool the surface of your tongue faster than your body can heat it up. They may even insulate it from an extreme temperature.
Article originally published in Brainspace Magazine Spring 2021