This week we have two winners. The first is by Jeremy Nelson
Everybody knows not to touch their tongue on a flag pole or metal for that matter in the winter! Obviously your tongue sticks to the metal. I know that conduction is taking place and that our tongues are much warmer than the metal, but why do our tongues stick to the metal?? Is it because of the temperature difference or because of conduction alone or neither???
The answer is that--both. The rate at which heat is transferred by conduction is determined by the temperature difference between the objects and their thermal conductivity. Metal is a good conductor, and flesh is pretty good as well. When you lick the flag pole, heat is transferred from your tongue to the sub-freezing pole. Your tongue, and the area around it, transfers heat to the pole (warm object to the cold) and the temperature of part of you tongue drops to freezing, and freezes to the pole. In the movie A Christmas Story a kid licked a flag pole under a triple dog dare! By the way, would your tongue stick to a wood telephone pole?
The second question is from Sarah Vold and Brian Knox.
We were wondering why, when it is somewhat nice outside, can you see your breath? We were walking home from class on Friday afternoon and it was around 60 degrees, a little bit humid and we were able to see our breath. Is it related to the humidity or the temperature?
We will be covering this topic after the first exam. Basically it is due to both the humidity and the temperature. You "you see your breath" you are forming a fog, and a fog can occur on warm as well as cold days. The key here is that you are mixing to different air parcels, the environment and the one from your lungs, which has a high relative humidity. Mixing of moist air is a non-linear process. To get a full appreciation (and answer) we have to discuss how to form cloud droplets.
You can send me your question on temperature by e-mail