Heat & Temperature

Today we started by staring at two beakers of water. Because you saw me before class with the propane torch, you knew that I was trying to make sure that one of the containers was at a much higher temperature than the other. A drop of food coloring in each of these two beakers (hot vs. cold) and you could see how the food coloring diffused much more in the higher temperature water. So, even though "temperature" is simply stated as that which a thermometer measures, you get a sense that it describes the random motion of particles that make up a substance.

It goes against your intuition, but what you feel when you say something is hot or cold is not "temperature." Rather, you feel the transfer of energy from a high temperature stuff to a low temperature stuff. This exchange of energy is what we call "heat."

Because the exchange of heat (energy) naturally and spontaneously occurs, you can take advantage of this. In class, we see this with a simple engine that turns a fan. This is also the basis of every engine (including the one in your car) that we've ever created. A temperature difference drives the exchange of energy, and we harvest some of this energy, conserving it in a mechanical form.

As we were physically transfering energy into a piston (by exchanging one end of it from the hot to cold reservoir), we realized that at the same time we were getting mechanical energy out of this deal, we were also always lowering the temperature of the high temperature reservoir and raising the termperature of the low temperature reservoir. Any good honors student could tell you what would inevitably happen: the two would equilibrate at the same temperature. This is not just the finality for our two beakers of water, but for everything in the universe. This is one of the predictions of what is known as the 2nd law of thermodynamics.