Mike_MC:
Trust me. Air or any gas can be liquefied given sufficient compression and removing the heat of compression. No exceptions that I know of. The only difference between a gas and a liquid it the density of the fluid. The higher the density the more “liquid like” the behavior, lower the density and the fluid behaves “gas-like”. Even water under reduced pressure (aka vacuum) becomes a “gas-like” substance. Our notions of liquid and gas are relative to our environment. If you lived on the Moon or Mars water could only exist as a gas (due to the low ambient pressure) or as ice (due to the low temperatures) which is really just a real dense fluid. Of course this really doesn’t mean anything except to engineers and others interested in the physical properties of substances. We often refer to air, or a gas as a fluid and it makes sense to us and I can appreciate the confusion it generates for others.

The rest of this is making my head hurt. I’m retired and have quit thing on a regular basis. Sometimes I think my IQ has dropped 20 points…

Ben Lanterman:
A closed jar without a fly will weigh n cubic units times the density of the air. Jar with a fly will weigh: (n cubic units X the density of air) less (the volume of the fly times the difference in the density of the air and the weight of the fly). With a sensitive enough measurement you could (?) measure the velocity of the air coming off the fly’s wings and impacting the bottom of the jar, assuming the scale is under the jar. It would appear as a pulsation due to the up and down movement of the wing. But if I were conducting this experiment I’d just wait for the little bugger to tire and settle down and I’d call it a static measurement. The BB and the water (or liquid) is exactly the same. I think we’re in close agreement, right?

Have a good day and let’s release those flies and go flying!
Miles.