Here was the original item:
The winner is John Burk (answer submitted via twitter. Oh, I know the first commenter was Patrick - but that was after the twitter submission. Patrick, I still will give you an honorable mention (which means I mention you in an honorable way).
Of course everyone was correct. This is a device to measure the thermal expansion of a metal.
The device is a cylinder with a metal rod inside. The two red arrows in the picture above indicate the location that steam enters and leaves the tube (to increase the temperature of metal rod). The green arrow is where a thermometer would go to measure the temperature of the rod. On the right end, there is a adjustable screw that is used to measure small changes in the length.
What is cool about this demo? First, think about one of the simple (but very useful) models of the nature of matter. We can model matter as though it were made up of atoms connected by springs. Here is an illustration of that from the text Matter and Interactions (Wiley).
Why springs? The model uses springs because the motion of a mass on a spring can be solved analytically. Here is the potential energy of a single mass on a single spring as a function of distance (from something).
This is supposed to be a symmetrical curve. The dotted line shows the total energy of a particle oscillating due to the spring. The key point here is that no matter what the energy, the average position of the mass will be the same. But really, the potential energy curve for a mass in a solid should look something like this:
Not symmetrical. This means that as the energy of the particle increases, the average distance changes. For the whole object, this means that as temperature increases, the energy of the particles increase. The average separation also increases.
