Recent content by bgwowk

For an ideal gas, pressure is indeed proportional to energy density per unit volume. That's because at constant volume, pressure is proportional to temperature which is proportional to energy. And at constant temperature, pressure is proportional to number density which is proportional to...

Negative. The energy content of an ideal gas depends only on temperature, not pressure. Here's what happens: As you compress gas into a scuba tank, the work done on the gas appears as heat in the gas. As long as the gas remains hot, it still contains the energy you put into it by compressing...

Once a gas expands so that its pressure is equal to ambient pressure, it can do no more useful work. But for air in a scuba tank that starts off at 100 times atmospheric pressure, whether expansion is stopped at one atmosphere or zero atmospheres (vacuum) makes little difference in total work done.

For whatever it's worth, I have a PhD in physics, so maybe I can help explain this. Steve Harris and cesiumfrog are correct that a compressed tank of ideal gas has no potential energy. It has only the kinetic energy determined by the temperature of the gas, which for a given temperature is the...