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Wow. The above science that Tom fails again to grasp, has certainly sent him into a tirade. Sorry. That rage is blinding you. Now you've brought in the need to explain gravity, which has little influence on the gas pressure in our engines.
Perhaps one day you will understand the difference between being outside the atmosphere and outside the gravitational well. 100 miles up is one but not the other. Please go figure it out. It's just math. Hint, gravity becomes relevant when very very large masses are available, such as gas condensing into a planet.
Turning the fan off? Remember speed is temperature, it's like cooling all the molecules to absolute zero Kelvin almost instantaneously. At zero Kelvin none of the molecules have any kinetic energy, speed, so none are gas. Zero pressure, not negative. Of course in the remaining volume, a complete vacuum, the boiling temperature will also be zero. Any energy added will tend to provide a gaseous molecule to bounce around and fill the container with a very slight positive pressure. My point of the analogy was to show that even one molecule, with gas momentum, will be a positive absolute pressure.
Tom Booth wrote:Gas in a 55 gallon drum will implode the drum.
No mechanism to do so. Gas inside a balloon doesn't implode a balloon. Put a collapsed tied balloon into a bell jar and apply a pump to remove the air. The balloon will try to fill the volume with the little residual air left inside when tied. Gas inside always pushes, a law before all other laws, observed many ways. Easy science. If you can't get that you won't get anything else. As Professor Baker used to say, "F=ma and you can't push on a rope".
The 55 gallon drum demonstration is also used to show how weak a drum is from external pressure. Less than 14 psi to crush/compress it. The Titian Submarine require around 6000 psi. Substantially more. The vacuum inside the drum did not 'pull' it in. It was crushed by outside pressure. The experiment will not work if done in a vacuum.
55 gallon drums are weak in compression, so are tank cars and all tanks. Very thick walls are needed to handle compression from the outside pressure. Walls can be thinner for internal expansive pressure, like your shop compressor or propane bottles. Even an oxygen bottle 2000 to 4000 psi, is way thinner than the sphere on the Alvin Submarine. 1/8 inch verses 2 inches, or there abouts.
Tom your education has missed many many areas needed to argue these points. Sorry again. Or as Molly Brown says "a pity".
P.S., Tom I see the progression of you picking up some of this science, backing away from you misguided ways, however it is very, very, very slow. Good.
Some of the things you've learned:
There is such a thing as internal energy.
Adiabatic temperature drop, verses, temperature reduction from heat removal requiring a temperature difference.
People think that nature makes gasses always push, even though molecules always attract and repel.
Temperature is molecular speed and momentum.
Gravity works because there is a very large mass.
The first law of thermodynamics prevents any perpetual motion machines of any kind.
Heat engine require a temperature difference.
It's easy to compress a gas, just smash it with a piston.
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