<Deleted my post, as you didn't refer to it anyway ... why quote it at all?>
Funny, I look at the videos presented here by AATW...
I'll leave that one to AATW. (Sharing is caring ... iCare
).
And the reason why is simple...gas, when released into a vacuum, is not, and cannot be "forced," into a vacuum.
Of course it can. Gas is always "forced"
from where the pressure is higher to where the pressure is lower - until there's equilibrium.
Why would gas care if the lower pressure is 0?
When any container of gas is opened, the gas is released with that amount of instantaneous pressure applied at the opening...with the following notable exception...
When the container is closed, there is pressure at the valve (the valve being closed, it makes no difference, if there's a vacuum on the other side or not).
Case one: No vacuum, lower pressure outside => open valve => pressure applied
Case two: vacuum (lowest pressure) outside=> open valve => pressure "magically disappears"?
Thinking of vacuum as 0 pressure, it's pretty much the same as low pressure ... just lower.
What is so significantly different about vacuum that it requires a "notable exception"?
Free expansion happens between two connected volumes/chambers; one contains a gas, the other "contains" a vacuum.
The chamber containing the gas is "pushed" one way by the "leaving" gas, but at the same time the other chamber is "pulled" the other way by the "leaving" vacuum.
With that specific (closed) setup all forced cancel each other out in the end and "no work" is done.
When the opening of the container of gas is exposed to a vacuum...in which case...the gas just freely expands into the vacuum.
Again: Free expansion does not apply to rockets. For the free expansion experiment you need a fixed amount of gas in a closed space (two connected chambers).
A rocket generates additional gas (through chemical reaction) and expels it into the "open", i.e. an "infinite" (at least compared to the amount of gas) space not connected to the rocket.
As I asked in my other post: For rockets to work in an atmosphere (which they observably do) kinetic energy needs to be "generated" somehow.
If in a vacuum this energy does not accelerate the rocket ... where does it go?
iC