Can Firearms be Fired in Space

[45_auto]

That's not the case. 55 grains is a measure of weight, the force of gravity on a mass.

No, 55 grains is a measure of mass, not weight. No gravity involved. A bullet that masses 55 grains on earth would also mass 55 grains on the moon.

The exact same bullet will weigh .00786 pounds on earth, and .00131 pounds on the moon.

Grains are a measure of mass just like grams or slugs. The grain or troy grain (Symbol: gr) measure has been defined in terms of units of mass in the International System of Units as precisely 64.79891 milligrams

Unfortunately, most people don't understand the difference and refer to grains, grams and kilograms as "weight" on earth.

If someone "weighs" 80 kilograms on the earth, they will also "weigh" 80 kilograms on the moon. The correct term in quotes would be "mass".

The corresponding unit to the pound (weight) in the metric system is the Newton, but no 40 kg woman wants to admit that she weighs 392 Newtons!

 

[denton]

First, there is no NIST standard for weight. Weight varies by a few to several tenths of a percent at various locations on the surface of Earth, so there can be no standard. Instead, NIST holds a standard kilogram which is a unit of mass.

Ever helpful, NIST has provided a standard definition of the acceleration of gravity, and that allows us to convert back and forth between units of weight, such as Newtons, pounds, and ounces, to units of mass like slugs and grams.

Unconstrained by man-made definitions, gravity does what gravity does. The definition is just a convenience that is meant to be helpful.

Well, maybe it's not all that helpful, because it facilitates the casual interchangeable use of weight and mass in non-technical literature. You can see a glaring example of this at Wikipedia, http://en.wikipedia.org/wiki/Grain_(unit)

The NIST Handbook 44 defines a grain as precisely 1/7000 of a pound. A pound is a measure of weight (force of gravity on a mass). If a grain is 1/7000 of a pound, a grain is a measure of weight as well.

Even NIST will occasionally reference pounds as though they were masses. When they do, it is by invoking the standard definition of the acceleration of gravity. They do that in Handbook 44, which doesn't help the confusion. (weight = mass x acceleration of gravity) If NIST does it, then I guess it won't hurt if we casually refer to a grain as a unit of mass, so long as we hold in mind that it is not really so, and we are invoking a unit conversion based on a standard definition of g.

A pound is a unit of weight, a grain is a fraction of a pound, so a grain is a measure of weight.

When you get around to firing your firearm in space, it will be the mass of the bullet that will be of concern in determining muzzle velocity, not the weight of the bullet.

 

[TEC]

Denton:

Technically, the Newton is a fundamental unit of force - (1 kg*m/sec**2), where in lies one of the most fundamental relationships in classic fizzix:

F=MA, force = mass x acceleration The formula and its implication -- that the universe is just a giant machine, that, once having been set in motion, has entirely predictable outcome, over time, independent of the influence of God. I think that (and perhaps some other things?) got him excommunicated.

Weight is also unit of force, usually thought of in terms of the force exerted on any mass by another mass by the gravitational force (Fg), or in the case of "Pounds", the mass of a person or object affected by the acceleration due to earth gravitational force (Fg), about 32ft/sec*sec if I remember correctly. Weight on the moon would be the force exerted on the same mass by the moon's gravity, etc.

Mass is conserved. Gravity is a fundamental universal force that depends, I believe, on the mass of an object.

When it all get too confusing, and my mind starts to ramble, I just try to remember what rhymes with mass and then think fondly, instead, of Angie Dickenson and my childhood, and one of my first favorite TV shows, "Men into Space"
Angie was, of course, the first TV astronauts wife and, IMO, the female counterpart of the Duke, John Wayne in all of my black and white memories.

 

[denton]

Technically, the Newton is a fundamental unit of force

Exactly.

Newtons and pounds are units of force. Weight is a force.

 

[double bogey]

Ok, we had someone fire an assembled bullet that was about -320F. Now we got to get him to do it in a vacuum, with lo/no gravity.

 

[MattShlock]

Who said the conservation of the center of mass was a substitute for momentum being a fixed constant in the universe that could neither be created nor destroyed? Hello!? Someones had one too many Big Bangs in the head. Just the concept of potential energy being converted to a vector quantity proves you wrong. Center of the universe notwithstanding.

It's like I'm talking to a bunch of illegal space aliens... Best and brightest my assumption!

 

[denton]

Matt.. Matt... Matt... Reason with me.

Does F=ma? I think you have to agree that it does. Everyone should recognize and accept that basic formula. F is the sum of all externally applied forces, m is mass, and a is acceleration

So think about you and a sack of cannonballs, out in space.

You and the cannonballs have a center of mass, no? Of course you do.

Now if there are no external forces applied to the center of mass of you and the cannonballs, then F=0. If F=0, then a must be 0. If a=0, the center of mass of you and the cannonballs is not changing speed or direction, i.e, is not accelerating.

So when you push a cannonball away from you (that's an internal force, and does not count as part of F on the center of mass), some or all of the rest of the system has to move in the opposite direction, else the center of mass will move. And that would violate F=ma.

It's the principle that propels rockets.

It's also one of the grand laws of physics. It holds true on a quantum mechanical scale, and it holds true in relativistic mechanics. It's one of the pillars.

If you can get a copy of Hatcher's Notebook, he has a very nice discussion of how it applies to firearm recoil.

BTW, in space, without friction or gravity, you actually do get the results that conventional recoil calculations predict. Here on Earth, with the rifle against your shoulder, not so much.

 

[climbnjump]

Hence, if you are stuck in space, having drifted away from your ship, holding a sack of cannon balls, you can propel yourself to the ship by throwing cannon balls away from the ship. Momentum of you and the cannon balls before you throw = momentum of you and the cannon balls after you throw.

Well, yes but...

So when you push a cannonball away from you (that's an internal force, and does not count as part of F on the center of mass), some or all of the rest of the system has to move in the opposite direction, else the center of mass will move.

Yeah, there we go. If you meant an overhand throw in the first quote, you wouldn't quite get the desired affect, right? Conservation of angular momentum and all?

 

[TEC]

Denton: Do you mean that in a dynamic system, every action has an equal and opposite reaction?! Very interesting. If that's so, then not only the systems mass, but also its momentum (and energy) would be conserved. Cool.

BTW, n the first episode of Men into Space, (just watched it on U-Tube last night) Col McCauley gets saved after he the gets knocked off the space ship, while on a space walk (with magnetic shoes) so he can use a cutting torch to cut a stuck coupling on the spaceship's booster. His crew track him down, fly the ship to where he is drifting away, and, with the rocket engines still ablaze, throw him a rope from the open hatchway as they pass. Pretty exciting stuff for the 1950's

So, i guess if you can fire a gun in space, then using a cutting torch works too, and throwing a rope from a moving space craft is also relativistically easy, as long as you thought to bring extra rope and a cutting torch along for the space trip.

The spaceship's name was the XMP-13 (experimental moon probe). I guess XMP-13 was the TV forerunner of Apollo 13, huh. And remember, LSMFT.

 

[Art Eatman]

Back some sixty years ago, dividing the weight (aardvark pounds) by "g" gave what were then called "poundals". That way you could differentiate between plain old weight and the mass for calculations for impulse, momentum, energy, etc. Dunno if that convention still holds.

 

[splattergun]

I am referring only to the idea of firing a gun in the vacuum of space here:


Physics was a long time ago but a similar topic actually came up about whether a dynamite explosion would expand forever and the professor gave an explanation that was not what I expected. According to him, since space is a vacuum, the explosion would occur, (Just like gun powder, dynamite has all of the essential chemicals required to oxidize),but it would quickly retract back in onto itself once the initial energy was expended and the force (or lack thereof) of the vacuum was greater than the remaining energy in the explosion. It was his opinion that most of the debris ( Mostly paper and carbon I would expect) would retract back into the vacuum.

I believe that the bullet would gain a lot of momentum and would continue to travel much further than it would on earth but I do not believe that the expansion of gases would reach near the same level that it would within an atmosphere and the bullet would not achieve near the same max velocity.

Just my own logic. But this would be a great experiment just for giggles.

this professor's hypothesis forgets other aspects of physics which affect the explosion. Mass, gravity, momentum, etc. There have been explosions in space. Apollo 13, for one. No retraction of gasses there. The debris field is still detectable to those tracking space junk. It is likely expanding, due to the gravity of the moon pulling the debris.

Another explosion, much larger, is a nebula. A star explodes, the gas and debris continue to expand until the gravitational fields of other bodies affect the momentum. The mass begins to stabilize in form and pockets of more mass begin to contract in on itself.

It is gravity that causes material from explosions in space to contract. Other bodies' gravity will pull in part of the debris as well.

The debris from a gunshot in space would soon be pulled toward the object of greater mass. Earth, in this case.

 

[dmazur]

Dunno if that convention still holds.

From this source -

Poundal

English units require re-scaling of either force or mass to eliminate a numerical proportionality constant in the equation F = ma. The poundal represents one choice, which is to rescale units of force. Since a pound of force (pound force) accelerates a pound of mass (pound mass) at 32.174 049 ft/s2 (9.80665 m/s2; the acceleration of gravity, g), we can scale down the unit of force to compensate, giving us one that accelerates 1 pound mass at 1 ft/s2 rather than at 32.174 049 ft/s2; and that is the poundal, which is approximately 1⁄32 of a pound force.

The poundal-as-force, pound-as-mass system is contrasted with an alternative system in which pounds are used as force (pounds-force), and instead, the mass unit is rescaled by a factor of roughly 32. That is, one pound-force will accelerate one pound-mass at 32 feet per second squared; we can scale up the unit of mass to compensate, which will be accelerated by 1 ft/s2 (rather than 32 ft/s2) given the application of one pound force; this gives us a unit of mass called the slug, which is about 32 pounds mass.

Yes, I remember the poundal. I have not encountered it since grade school, which was a while ago.

As explained above, poundals and slugs are two different approaches to the same problem and are not used together. Unless "mass hysteria" is desired...

 

[dmazur]

...the force (or lack thereof) of the vacuum was greater than the remaining energy in the explosion...

Well, this is the first time I've seen "vacuum" described as a force.

An explosion under water creates a temporary low-pressure region, once the chemical reaction of the explosive stops. Water rushing back creates a force which seeks the lowest pressure outlet (the side of the bubble nearest the surface.) I understand this is what creates the geyser effect from something like a depth charge set "shallow" rather than "deep".

However, a vacuum isn't a fluid but is, of course, nothing. So I believe the "bubble collapsing" description was misapplied.

 

[aka108]

Does it really matter or will a correct answer change the course of Western civilization? None of us will go there to find out.

 

[Clark]

When we shoot a rifled gun on earth, the rotational reaction on the shooter gets offset by the rotational reaction of the target. The earth stays on the same path.

But in outer space when you shoot a gun, you never get rid of the spin. You can average it with your big space ship when you come back from your space walk. But the other cosmonauts will complain, "Hey! Stop bringing all that spin in here!"

 

[jim243]

It was his opinion that most of the debris ( Mostly paper and carbon I would expect) would retract back into the vacuum.

Interesting, creating a vacuum within a vacuum, not likely. That only works where there is atmospheric pressure to push the material back into the vacuum.

Jim

 

[barnbwt]

"Can Firearms be Fired in Space"
I think the little skirmish our boys had with their Russian counterparts on the Moon speaks for itself. Tragic misunderstanding, really; the cosmonauts merely needed a lift home since theirs was a one-way mission.



TCB

 

[YZ]

Unfortunately it was the astronauts who needed a lift both ways from the Russians after the shuttle program was grounded.

Anyhow, I just came back from space. Turns out a certain Senator [moderator watching] has been there for some time. So NO THEY CAN'T.

 

[MattShlock]

Matt.. Matt... Matt... Reason with me.

Does F=ma? I think you have to agree that it does. Everyone should recognize and accept that basic formula. F is the sum of all externally applied forces, m is mass, and a is acceleration

So think about you and a sack of cannonballs, out in space.

You and the cannonballs have a center of mass, no? Of course you do.

Now if there are no external forces applied to the center of mass of you and the cannonballs, then F=0. If F=0, then a must be 0. If a=0, the center of mass of you and the cannonballs is not changing speed or direction, i.e, is not accelerating.

So when you push a cannonball away from you (that's an internal force, and does not count as part of F on the center of mass), some or all of the rest of the system has to move in the opposite direction, else the center of mass will move. And that would violate F=ma.

It's the principle that propels rockets.

It's also one of the grand laws of physics. It holds true on a quantum mechanical scale, and it holds true in relativistic mechanics. It's one of the pillars.

If you can get a copy of Hatcher's Notebook, he has a very nice discussion of how it applies to firearm recoil.

BTW, in space, without friction or gravity, you actually do get the results that conventional recoil calculations predict. Here on Earth, with the rifle against your shoulder, not so much.

Who says? Energy translated. Force applied. Mass moving. Momentum created! So simple even a Martian could see it at Area 51...

 

[Robert]

Ok let's call this one asked and answered. And then some.