firing gun on the moon

i read in a comicbook that someone firing a handgun on the moon could reach escape-velocity because of the recoil. normally i would not take something from a comicbook for serious but it was written by warren ellis and i am not sure if it was a joke from him or if it is true.

any explanations to this?

could i travel from the moon to earth firing a m-16 with enought ammo(only joking)?

Off the top of my head, that's impossible. The escape velocity can be calcualted (find some elementary mechanics web site) and the recoil won't be enough

Moon's mass in relation to Earth's (1/81 = 0.012) and the Moon's radius in comparison with Earth's (1080 miles/3960 miles = 0.273). Take Moon's mass and divide it by its radius (0.012 divided by 0.273 = 0.044) to come up with a figure of 0.044. Take the square root of that number, which is 0.21. Multiplying 0.21 by 7 miles per second gives the answer we are seeking. The escape velocity at the Moon is about 1.47 miles per second, compared to earths 7 miles per second

COncidering something like a barret lt 50 has a muzzle velocity of just over a half mile a second, if you ignored your mass, and the guns mass, it still would be impossible to do. best you would get is a slight decrease in your mass, or a Lift into the air. But nothing nearing escape velcoity.

Now you take a small asteroid with about a 200 meter diameter.. then you might be abel to do it.

But you still need to figure out a way to fire the gun in a vacuume

Originally posted by Jehosephat
best you would get is a slight decrease in your mass, or a Lift into the air.

I thought there was not any air on the Moon

Now you take a small asteroid with about a 200 meter diameter.. then you might be abel to do it.

But you still need to figure out a way to fire the gun in a vacuume

Easy. You just pull the trigger. The powder contains both the fule and the oxydant.

no, you need oxygen to complete the reaction

No, oxygen is part of the formula. Gun powder doesn't burn, it explodes.

Quite true. I remember an exercise I used to do with the kids at school. Ran along the lines "You have crashed on the moon, what items do you take from your ship to walk back to the moon base, yada yada"

They have a list of items they have to choose from and have to rank them and also decide what to leave behind. Everyone leaves the .45 pistol behind, but apparently it can be pretty handy to cross cravasses and the like using the recoil.

But not off the moon, though, that would take something a little bigger than a .45.

That is actaully a very good thing to study. There is another one in a kind of "Survior" moitief.

The porlbem is a firearm would end up doing more harm then good in the long run.

For the moon one I allways put Oxygen as #1... but that does not seem to be the right answer for no reason.. guess it is okay to suffocate for a little bit

As far as putting Oxygen in the bullets, I hope you know how to handle missfires and fouling of the weapon. as little pockets of oxygen become thier own seperate combustion chambers

not a good idea to fire a gun on the moon as the bullet could easly go all the way around it to get you in the back

Lol. Anyway, the gun wouldn't be much help if you're planning to go to the moon. But you might use it as your makeshift propulsion system..

What about a rocket launcher at very close range? Perhaps... the ground. Think that'll work?

I think you'll find this is an exercise in theory, not practicality. I am not suggesting that a pistol is the easy way to move around big distances on the moon, I am sure there are much better and more practical methods. However there would be thrust involved and it would in theory help with jumping small distances (i.e. cravasses was the example I used, they don't have to be big).

There is a slight difference between the contact made between a golf ball and club, and the controlled explosion of a pistol firing.

Here on earth the recoil from a pistol can knock people back a few feet, little fellas to be sure, but I have seen it happen. I remember one little old guy at the pistol club shooting a Desert Eagle and in his case it was a couple of yards with each shot.

Hehe ever play quake? Rocket jump my good man! Blast them toes and propel yourself skyward!

Well maybe you'll run into aliens on the moon, and the gun might scare them off You can never be too prepared.

Originally posted by Terapin
(...)
Despite the lesser gravity you still have to over come the inertia of say 200LBS. (...)

True, but there is a difference to be made between your mass, which doesn't change there, and your weight: because of gravity on the moon, which is about 1/6th of that on earth, your weight on the moon would be around 35lbs, while your mass remains at the same 200lbs... This means that less effort is needed to produce the same movement.

simcity says:

"not a good idea to fire a gun on the moon as the bullet could easly go all the way around it to get you in the back".

No.

This is one of the reasons why I believe that basic physics, along with at least one semester of the calculus and statistics, should be a required subject in high schools. People who do not understand basic science and math don't understand the way things work, and, like many people here, fall for any load of pseudoscientific rubbish as long as it sounds impressive.

Work with me on this, simcity: the attraction of gravity is completely independent of any lateral motion imparted to an object (as long as you don't take air resistance or support a la gliding into account, which you wouldn't on the Moon, anyway).

If you hold a bullet at arm's length, say, four feet) and drop it to the Moon's surface, it will take 0.86 seconds seconds to do so, given that you can plug in the moon's mass and the bullet's mass (close enough to zero not to make any difference) into Newton's Law of gravity equation: F =G mM/R^2 , where G is the gravitational constant, m and M are the masses of the bodies being considered, and R is the distance separating the masses m and M.

That's if you just dropped it. Suppose you fired it straight out (parallel with the moon's surface) from a pistol which gave it a average velocity of, say 300 m/sec (this is about the muzzle velocity of a .45 ACP cartridge)?

Answer: still 0.86 seconds, because the attraction of gravity is completely independent of any lateral motion imparted to an object. Now, given the assumption that the gun is fired parallel to the moon and that the area has a flat surface, the bullet fired at the average Vm of 300 m/sec will travel 258 meters (about 850 feet) before hitting the ground.

Besides, even if the bullet did fly all the way around the Moon, it still wouldn't hit you in the back of the head, because, in the 30.55 hours it would take the bullet to make the trip, you would've probably gone back into the spaceship for lunch and a nap.

hehe and what if i would fire a gun from the moon directed to earth, would it hit earth one day considering it does not collide with the iss before??

how close to earth would i have to fire the bullet to bring it into earths gravityfield, and would it dissolve(because of the heat) entering the atmosphere?

btw. am i right that the biggest problem with going to mars is reaching escapevelocity to go back again, from a technical point of view(ok, probably Mr.Google could answer me this one)?

asuming there were minerals worthy of transport from moon to earth the transport itself would not be the biggest problem, again from a technical point of view?



[edit on 9-3-2005 by feyd rautha]

feyd rautha says:

"hehe and what if i would fire a gun from the moon directed to earth, would it hit earth one day considering it does not collide with the iss before??"

If you fired it at the earth, it would probably miss; you'd have to fire at at a place where the Earth was going to be, which involves orbital mechanics and a humongous gun to get the bullet into lunar escape velocity in the first place.

"how close to earth would i have to fire the bullet to bring it into earths gravityfield, and would it dissolve(because of the heat) entering the atmosphere?"

(1) it depends on the trajectory of the Earth, but if you're still talking about firing from the moon, the bullet would have to have at least some earthwoard vector and be closer than one of the Lagrange points. (2) Whether it burns up or not depends on its composition and the angle and velocity it has when it enters the Earth's atmosphere.

"btw. am i right that the biggest problem with going to mars is reaching escapevelocity to go back again, from a technical point of view?"

From a plain old planetary physics point of view, getting the ship into Earth orbit would cost you the most as far as expended energy is concerned, since Earth's orbital (and thus escape) velocity is higher than that of Mars.

The logistics of such a program would be very big, because you have to determine if you can mine fuel on Mars to get you back to Earth. This is a toughie, because without mining either your fuel or oxidizer on Mars, you might have to have a hugely expensive set of fuel 'caches' along the way, but if you planned on mining and couldn't get your apparatus to work, you'd die; simple as that.

But the biggest problem -- the one which dwarfs all the rest -- is building and sustaining the national or international will to do this thing.

"asuming there were minerals worthy to transport from moon to earth the transport itself would not be the biggest problem, again from a technical point of view?"

Technically, that wouldn't be a big deal; all you'd have to do is to put your minerals into a steel can which would be launched by rail-gun into lunar escape orbit, captured by the Earth's gravity well, and parachutes into the ocean somewhere. No costs for life support; no minimizing 'g' forces to keep the passengers from being squashed, because there wouldn't be any; and you can pick the most energy-efficient ballistics, even if it took six months and nineteen loops to get to the Earth, because, again, you don't have any passengers to starve to death in the can.

But even so, the energy costs for the rail gun would be pretty high, and you'd want to make sure that whatever exports you sent back to Earth were valuable; otherwise, it just wouldn't be cost-effective.

Fyed, I sugggest you find a copy of The Moon is a Harsh Mistress. You should be able to find it at your local library.

You would probably find it an interesting read.

Originally posted by HowardRoark
No, oxygen is part of the formula. Gun powder doesn't burn, it explodes.

Eplosion is just fast burning... at least in case of powder.
High Explosives (C4/RDX, TNT) have fuel and oxidizer in same molecule meaning part of their energy comes from disintegration of molecular structure.
PS. Those have quite nice molecule names like cyclotrimethylenetrinitramine... that's the stuff in C4.

Originally posted by Off_The_Street
This is one of the reasons why I believe that basic physics, along with at least one semester of the calculus and statistics, should be a required subject in high schools.

More likely basic physics should be taught in ordinary schools... but of course christian fundamentalists would jump against that because they don't find that from their book.