allancw » August 12th, 2016, 5:58 pm wrote:Simon and I had a back and forth a couple years ago that I'll briefly repeat -- I haven't gone back on this thread to see if something similar has been posted, so forgive the possible redundancy.
I asked Simon to imagine the two of us floating in space, me with a loaded 9mm pistol. Would it be ok if I pointed it at him and pulled the trigger. Simon said, sure, it wouldn't shoot in the vacuum (this may be a bit oversimplified).
If you go to Youtube you'll find a vid wherein a pistol shoots just fine underwater. Mmmmm. See, the bullet plus casing contains all needed to go off, so being underwater is not a problem.
Yes, a vacuum is a bit different, but those who feel that rocketry won't work in a vacuum... are you sure enough to say 'OK' to my pulling the trigger? (I think Simon changed his mind.)
The point here isn't the bullet coming out of the barrel -- which I am sure it would -- but rather the recoil. The recoil is the point. Imagine a hundred shots per second.... via the continuous recoil you have a rocket, no?
Again, sorry if this is redundant.
I'm new here and skimmed some of this thread. I also question whether rocketry would work in a vacuum. I used to take it for granted, but not so sure. Interesting question. A gun is different than a rocket, though I get your analogy. Imagine floating in space and you fire a gun. The bullet (gasses) will push back on the chamber, which in turn pushes back on the shooter. I can see the recoil pushing the shooter back, but the bullet would probably also fire...perhaps at a lesser speed than in gravity environment (simplified for no atmosphere), but maybe still enough to be fatal. The bullet/gasses are going to take the path of least resistance, but also you have an equal and opposite reaction. You can feel the recoil of a gun, and I have no doubt it would propel you backwards in space.
A rocket just floating in space firing a rocket engine I'm not so sure. There's nothing to push against. I know they say the rocket is pushed upward by the thrust, but I wonder if it would just fire and fizzle in space? If the gun were to be free floating in space and could spontaneously fire the gun and bullet would presumably shoot off in opposite directions and I'm sure a formula can prove that.
Now imagine you are flying towards the moon in outer space at 25,000 mi/hr and you need to stop quickly and your engine happens to be facing forward and you fire it at full thrust. Is that going to slow you down to a halt in a vacuum? I'm not convinced yet. There's still the question of igniting the rocket in space, but we can assume the fuel is self contained. Seeing the Movie gravity made my eyes roll constantly. Like the whole Fire extinguisher propellant. I don't think that would happen period...without even considering the other stupid assumptions.
All that said, I don't think we could have gotten a lander to the moon and back....and it would have been far to risky to try.
Another thought is imagining an airplane (or helicopter) in space. The propellers or jet engines would have no atmosphere to Push. They would just spin and spin and go nowhere, no matter the angle of attack of the blades/wings. Imagine swimming in space. Your arms spinning and legs kicking, but you go nowhere. This is always a pet peeve with sci fi movies like Star Wars, Armageddon, buck rogers, with x wings and tie fighters banking and turning like they are on earth in a vacuum. Not possible. I think maybe the same with rocket engines. They just fire and you float stationary.