What in the world about a cold metal pole tempts us to stick our tongues to it? And why does our tongue stick to metal in the winter? Well, besides the simple answer of ‘it freezes,’ it all boils down to the scientific term, thermal conductivity.
Water freezes when it reaches a temperature of 32 degrees Fahrenheit. Your tongue has a thin coating of moisture on its surface. The pole is made of metal. When this moisture makes contact with the icy pole, the liquid on your tongue turns to ice. And unless you are going to stand there until the temperature warms up, nothing short of heating up the metal or a stream of warm liquid will break this bond.
Not all materials that are below the freezing point will react in this manner. It all depends on the properties of the material. Thermal conductivity is how a material conducts, or moves, heat. A material with high thermal conductivity will transfer heat from a warmer item to a cooler item very fast.
♦ The Colder the Metal, The Faster the Freeze
The amount of heat that is transferred from the warmer object to the cooler object is equal to the product of the thermal conductivity multiplied by the temperature difference between these two objects. This explains why it is that, if the pole is 20 degrees, your tongue will freeze to it faster than if it were 30 degrees. The difference in temperature between your tongue and the pole determines how fast the heat moves from your tongue to the pole.
♦ The More the Metal, The Longer the Freeze
Metals are excellent heat transmitters so it is logical that the more metal that is present the longer your tongue will remain stuck. If you eat ice cream with a silver spoon, you will experience the same thing that happens when you stick your tongue to a metal pole. However, you will be able to loosen it in much less time with a lot less effort because your body is always supplying heat to your tongue. When a spoon freezes to your tongue, you can raise the temperature of the spoon sufficiently enough to loosen the icy bond in a short time and with a little help from the warmth of your breath.
It is not always the size of the metal that determines the length of the tongue freeze, but the properties contained in those metals. For instance, a stainless steel spoon will not stick to your tongue like a silver spoon. This is because, in scientific terms, the measurement of thermal conductivity of a silver spoon is between 406 and 430, while that of stainless steel is lower, between -24 and 36.
♦ It’s Not Just Your Tongue
Your tongue is not the only thing that will stick to metal. Any part of your body that has moisture on its surface will stick to metal that is below freezing. Although those old metal ice trays we used in the past captured many a damp finger before we replaced them with plastic, they provided a valuable lesson to our experience as kids. By knowing what happens when our tongue, or damp finger, touches that metal ice tray, we could imagine how scary it would be if it were our tongues stuck to a pole.
If you have children, you know they have experienced this temptation, or will in the future. It may even be in the form of a dare from someone. You can head off any danger and teach them an important lesson by performing a fun experiment at home. Use a small metal object and your own freezer. Show them how the moisture between their skin and the metal turns into glue. Then ask them to imagine what would happen if the metal items were larger and the temperature colder. When done in a controlled situation, on a small scale with reinforcements, like a bowl of warm water nearby, the consequences will be a lot less serious but still reinforce the idea that it is NOT a good idea to stick any part of your body to cold metal in winter. It might just help to keep them out of a much more dangerous and sticky situation in the future.
You can find a list of thermal conductivities at: en.wikipedia.org/wiki/List_of_thermal_conductivities
For more information about metal’s thermal conductivity, go to ccmr.cornell.edu/education/ask/index.html?quid=777