Low Gravity and Recoil

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No.
Combustion requires a fuel and an oxidizer.
You know, like gasoline and air.

Strictly speaking, smokeless gunpowder does not "burn."
As I said before, nitrocellulose is a single unstable chemical compound. Well, a family of chemical compounds because cellulose is pretty variable in polysaccharide chain length. The nitroglycerine in double base powders is a single unstable chemical compound.
When "ignited" by a primer, it decomposes energetically, generating the large volume of hot gas that drives the bullet down the barrel.
 
From a simple question on Newton's three laws of motion and conservation of momentu to thermal dynamics to chemical reactions and Starship Troopers?

Really?

*sigh*

Force X is force X no matter where it's applied. Mass Y is mass Y...no matter where it's located.

If force X is applied to mass Y, the acceleration on the action/reaction system will be the same. Hence, felt recoil will be the same on the moon as it is on Earth. It will be the same at sea level as it is on the summit of Mount Everest.

Simple.
 
No.
Combustion requires a fuel and an oxidizer.
You know, like gasoline and air.

Strictly speaking, smokeless gunpowder does not "burn."
As I said before, nitrocellulose is a single unstable chemical compound. Well, a family of chemical compounds because cellulose is pretty variable in polysaccharide chain length. The nitroglycerine in double base powders is a single unstable chemical compound.
When "ignited" by a primer, it decomposes energetically, generating the large volume of hot gas that drives the bullet down the barrel.

After a bit of research, I realize I misunderstood what a catalyst was. But I will also point out that your post lacks some basic information to provide understanding. It takes more than "It doesn't burn, it decomposes" to explain your point. Clearing up a few definitions of words goes a long ways towards understanding. (That's why it's important to know the difference between a magazine and a clip and a gun and a rifle.)

While the environmental conditions are different than inside the barrel, placing smokeless powder in a free pile and igniting it does indeed produce flames and heat. The gases exiting the muzzle produce a flash of flames. The gases released by the decomposition of the powder does burn. In the same way, wood does not burn. Heat causes the release of gases from the wood that combust. If this is correct, wood and smokeless powder do not burn. They decompose when exposed to heat, releasing combustible gases.

It would go a long way towards understanding if you simply explained this to begin with
 
I am sure a technical treatise on propellant chemistry would have been a big help, but I am just not motivated to write one. It is not my main field and the necessary references are no longer readily available to me. (Which is a story in itself.)

Yes, it is commonly held that the muzzle flash is propellant gases igniting when they hit air. Hot carbon monoxide is the main underoxidized component, and it will do that.
 
MistWolf,

I can try to clarify but do not claim to be an authority on this subject. The confusion comes from the chemistry of explosive reactions. The propellant gas is generated by the fuel/oxidizer reaction. The fuel is typically oxygen starved and does not fully combust. When un-combusted but nevertheless hot fuel and byproducts reach the muzzle, they combust in our oxygen atmosphere which produces the flash. If the fuel was 100% fully oxidized and consumed in the cartridge, there would be minimal (if any) 'burning' outside of the casing itself.

While some reaction products may be flammable, the propellant gas itself is not 'burning' per se. Likewise, the gases in a wood fire are not themselves combusting necessarily. The wood combusts in an oxygen rich atmosphere when heated and the cellulose/sugars/sap/stuff in the wood undergo a similar chemical transition. CO2 and water and other stuff is released. Those gases, are not 'burning'. Some gases are flammable but are usually a result of incomplete oxidization. In short, don't mistake the gas products for the reactants...the gases are not necessarily combustible.

Take for instance this simple example:

2H2 + O2 -> 2 H2O

This may not be the best example but you can see that the fuel is molecular hydrogen and the oxidizer is molecular oxygen. The product will be in the gas phase at the reaction temperature but is not a combustible gas.

There is a good discussion of incomplete combustion with examples of hydrocarbon combustion on wiki:
http://en.wikipedia.org/wiki/Combustion

In other low explosives, like blackpowder, very little combustion products are gases (which are necessary to produce the pressure to propel our projectile). The rest are aerosols (solids/liquids particles in a gas) which eventually foul up the barrel. Just like smoke from a wood fire is an aerosol. Those oils and resins and particles produce the soot in our chimneys and gunk in our BBQ smokers.

The production of hot gas is why we do the chemistry (from automobiles to propellants). The hot gas is what we use to do the work. I hope this helps but then again I may just be full of hot air :)

-B
 
You'll be knocked off your feet easier because of the lower amount of friction from the ground. The projectile will travel farther before hitting the ground. Thats about it. It will feel the same to your shoulder.
 
As to the OQ, the physics recoil will be the same. Recoil is a conservation of momentum effect based on mass, not weight. So all the numbers will be the same.

I think the felt recoil will be different, though. The gun and the bullet have equal momentum in opposite directions. The gun momentum transfers to my body (or body + gun system) and I dig in my heels to transfer momentum to the ground. Lighter gravity holding me down will affect the way I am coupled to the ground and I think it will FEEL different.
So where do I get my ticket to Hong Kong Luna to try it out?
 
Interestingly enough....Woody Woodpecker used a cartoon shotgun to illustrate rocket power in the epic movie 'Destination Moon' (based on Heinlein's book of the same name). :D
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A shotgun is an interesting choice for the surface of the moon. Without a significant atmosphere, there is no impetus for the shot to scatter.

Is air resistance really what causes pellets to scatter? I would think they would jostle each other out of the shot cup regardless.

I can't add anything to a physics discussion here, but a shotgun loaded with birdshot might be an ideal weapon for a near-future space combat scenario. No atmosphere or gravity means the pellets never slow down so they're just as fast at 100 yards as it they are at the muzzle. Wounding power is not a problem, since just one pellet going through a spacesuit would be lethal in a vacuum. If the fighting is inside a space station or other spacecraft, the small pellets are less likely to damage vital systems inside the bulkheads or penetrate to the outside. You heard it here first guys: birdshot is the weapon of the future.
 
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Never say never!

When that big rock hits earth in 2012, and you get knocked out of your backyard into space, you might need that shotgun to get back down. :D

If you end up on the moon, get the air mask, stay away from the astronauts with the red names over their helmets, and use your knife on the rest as much as you can (more points dont ya know). :D
 
Aggie, while you are right what temperature is, you mistake that space, with no matter, has no temperature, unless you mean by "no," you mean "absolute zero" which is as cold as it gets.

Plus an object in deep space sits at "microkelvin" which is very near absolute zero.

I'm not a doctor.
 
No. I mean that space, or the absence of matter, has no internal kinetic energy (as far as we know, discounting any dark matter or dark energy which is still somewhat controversial). Since there is no matter in 'deep space', for all intents and purposes, it makes no sense to talk about the temperature of the void. I have never heard of space being at 'microkelvins' but will entertain any references you can provide. As far as I know, the cosmic microwave background spectrum indicates that the average temperature of the primordial matter in the universe is approximately 2.7K, which is indeed cold but no where near absolute zero. It takes a lot of work (both energy and labor) for scientists to reduce the entropy of laboratory systems and achieve lower temperatures. Still, the 2.7K CMB is still a measure of material energy, not that of 'space'.

Cheers and Gig 'em Ags.
 
Right. Temperature is a physical property of matter. How much matter is there in a vacuum? Not much. Wikipedia says that the atmosphere of the moon has about 80,000 atoms per cubic centimeter. That's not much.

Anyways, temperature is a property of matter. If there's only an infinitesimal trace of matter, then it doesn't really matter how hot or cold it is since there isn't enough of it to really have an effect.

If you like, it's not entirely unlike firing a gun inside a Thermos.
 
Rover gun

Can you guys help me pick a rover gun?

Do flash suppressors work on the moon?
 
You'll be knocked off your feet easier because of the lower amount of friction from the ground.

No, it wouldn't. It's not about weight. It's about mass and momentum. Your body's mass is the same, no matter where it is. If the recoil would knock you off your feet on the moon, it would do it on Earth.
 
WNTFW, you wouldn't need flash suppressors because there is no free oxygen to combust any unburned fuel or unstable reaction products.

1911Turner, I agree. Friction is not only a function of normal forces but also the properties of materials in contact and their corresponding Van Der Waals forces. Friction may be greater than some Earth surfaces or it may be less...but friction is not the issue. In fact, if friction were less on the moon, you would have less torque applied to your body and thus less rotational (fall on your butt) motion and more translational (slide backward) motion, as if you were on ice skates.

BTW, how do I quote messages. I can't find the "quote/multiquote" button and am getting annoyed! Found it in the FAQ but can't find it on the thread. Thanks in advance.
 
Aggie, per your temperature comments, if you say the universe is around 2.7 Kelvin, that's fine with me. Absolute Zero is 0 Kelvin, and water freezing is 273, if I remember my scales right. Thus, space is damn cold, by your own reasoning.
 
Continue to believe what you want but you are wrong on this one and none of my 'reasoning' supports your conclusion. Please carefully re-read my comments. I am happy to discuss physics with anyone at anytime but let's keep open minds and swallow our pride. This will be my last attempt before respectfully removing myself from this conversation.

Space is a vacuum. It is not hot. It is not cold. It is nothing. My 'reasoning' cannot be clearer.

As Kozak says, it is like being in a vacuum insulator. The point is if you fire your gun, it will heat up rapidly and it will not cool itself (strictly by means of thermal radiation) efficiently at solid temperatures. Why? Because there is nothing to cool it...because space is not cool...because there is no fluid to convect heat away...because there is no matter...because it is space...which is nothing.

My overall thesis if I could summarize in a few concise words: space is not cold.
 
Re: BTW, how do I quote messages. I can't find the "quote/multiquote" button and am getting annoyed! Found it in the FAQ but can't find it on the thread. Thanks in advance.

It is easier just to discuss & debate hypothetical situations that will never happen than to use the quote feature.
 
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