Blog of Veikko M.O.T. Nyfors, Hybrid Quantum ICT consultant

Quantum Mechanics demystified, a try

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Hot gas is heavier, eh?

It was once in 1990’s I was in a hotel’s sauna in Bracknell, UK. Amazing, but it was actually pretty good one, stove was big enough to give a good heat on the upper bench. There was another person sitting on the lowest bench as well. Suddenly I hear from there: “Will you please throw some water on the stove, it’s getting a bit too chilly”. I ate my astonishment and threw a bit, but not much.

Individual downstairs really didn’t get it. Hot air is rising up whereas colder air is flowing down. Just like with hot-air balloons, you can fly with them by warming the air inside the balloon. Well, not all people around the world can be professionals in sauna-bathing I thought and forgave. Instead of saying “get up here”.

The other day I was reading book “The Feynman lectures on physics” and got my eyebrows raising slightly. It was told in there that when gas is warmed up in a closed pot it gets heavier. This is due to the molecules starting to vibrate faster as they are warmed up. And as we all know, mass increases as the speed rises according to formula:

\[m=\frac{m_{0}}{\sqrt {1-\frac{v^{2}}{c^{2}}}}\]

What on earth! Do I need to take lower benches in sauna from now on? Would it really be hotter there? For a moment I thought I had been wrong, but I was mistaken! Do I need to forgive myself instead of the person on the lower bench. :-)

All sauna enthusiasts, relax. After a second thought I realized what’s up. The volume of the pot doesn’t increase. Whereas the hot-air balloon expands as air inside gets heated. Density decreases causing the overall effect of balloon going up by Boyle’s law. As do the hot air in sauna.

More on Special relativity at my blog.