Physics Question

[Loomis]

Sound waves do not propagate in a vacuum.

Therefore, the gun does not go "bang" regardless wether anyone is present or not. So, to make it perfectly clear...there are no sound waves in space, therefore there is no sound in space.

As for the first question...When the gun fires and the slide begins it's rearward motion, the spring will compress, and then the compression of the spring will impart a force on the frame and cause the frame to move backwards to "catch up" to the slide

The "opposite and equal reaction" (as described by newton) from the bullet is going to be seen on the breech face, and thus the slide...NOT THE FRAME. Therefore, the CG of the reacting mass(slide) is not lower than the bore centerline, it is HIGHER than the bore centerline. Initially, in the first fraction of a microsecond, the muzzle flip will be down, not up. Once the spring compression begins to cause movement of the frame, the muzzle flip will reverse back to what we are accustomed to.

Because the spent gasses also have mass and will continue to produce "thrust" on the gun long after the bullet leaves the gun and the gun starts moving, the direction of the gun and the direction of the bullet WILL NOT FORM A STRAIGHT LINE. The deviation from a straight line will be very small, however.

 

[brickeyee]

The center of exactly what gravity in a weightless environment?

While gravity may not be present mass still is.

The 'center of gravity' is the same as the center of mass, and that is the point motion will be about.

On earth we have gravity. so locationg the center is not hard.

 

[Loomis]

There's no such thing as "absence of gravity". All matter has it's own gravity.

But that is besides the point. A force applied off-center to a mass will cause the mass to rotate due to inertal forces resisting the applied force create a couple...THATs TORQUE. Earth's gravitational pull has NOTHING to do with it.

Ok, mr physics, why are you using that screen name since you just proved that you are physics impaired?

 

[JesseL]

Sound waves do not propagate in a vacuum.

Therefore, the gun does not go "bang" regardless wether anyone is present or not. So, to make it perfectly clear...there are no sound waves in space, therefore there is no sound in space.

But in the immediate vicinity of the gunshot in space is not a vacuum. There is a quantity of rapidly expanding gas, roughly equivalent in mass to the original powder charge.

Therefore a gun in space does go bang, if you're close enough to hear it.

 

[Claymore1500]

Zen riddles
aside:

Sound waves do not propagate in a vacuum.

Therefore, the gun does not go "bang" regardless wether anyone is present or not. So, to make it perfectly clear...there are no sound waves in space, therefore there is no sound in space.

Ok, I didn't REALLY expect anyone to try to seriously answer my "zen riddle", but since you did, I would like to point out that "sound waves" are nothing more than air movement, Having said that, I submit that, IF, no reciever (ears, microphone, or what ever) is present to translate the moving air to sound, There is no sound wether in space or the middle of Rhode island.

Prove me wrong, I dare you!

NOTEIt's all in fun guys

 

[rcnixon]

There is some confusion, as someone pointed out, about the center-of-gravity and the center-of-mass. Also, I believe that the gun won't cycle at all. The falling hammer will impart a small force moving the muzzle downwards, very slowly, rotating about the center of mass. As the powder burns, the expanding gasses force the bullet down the barrel. This (and the gasses escaping the muzzle behind the bullet) will cause the muzzle to rise, again rotating about the center of mass. Someone else mentioned the ultimate limp-wristing; I don't conceive of any resistance to the backward, rotating motion that would allow the barrel and slide to unlock. There will be a rotational force imparted from the rifling, again as some else pointed out, causing a rotational movement. Now, would enough initial forward velocity allow the action to cycle? The math of this gets into differential equations and is beyond my worn-out skills from long ago. Anyone out there got mathlab or a handy engineering or physics student they can bribe into looking at this?

Russ, who will post another physics quiz in a moment

 

[Owen]

the pistol will spin around its center of mass.

In common parlance, center of mass = center of gravity.

 

[rcnixon]

BTW, Claymore, there most certainly is sound, if in an atmosphere. The physical disturbance is there whether perceived or not. In a vacuum, no. Ponder this as well; time, as we know it, does not exist, t is an artificial constraint placed on the universe by humans so we can understand it better.

 

[the foot]

You would absolutely have a remotely-fired limp-wristed jam on the first attempt. That being said, the action/reaction/blah blah blah would result in the weapon doing cartwheels.

 

[Loomis]

Wrong again, claymore:

Sound is energy, not the perception of energy. Therefore, no reciever is necessary for the presence of sound.

 

[Loomis]

rcnixon:

The falling hammer will cause muzzle to rise, not fall. As the hammer spring pushes hammer forward, it also, at the same time, pushes gun towards hammer. When the hammer strikes the gun(or gun strikes the hammer, depending on how you look at it) the relative motions of the two cease.

 

[Claymore1500]

BTW, Claymore, there most certainly is sound, if in an atmosphere. The physical disturbance is there whether perceived or not. In a vacuum, no. Ponder this as well; time, as we know it, does not exist, t is an artificial constraint placed on the universe by humans so we can understand it better.

Just a couple of points, Agreed the physical disturbance is there, But it does need to be translated into sound by SOMETHING or it is simply moving air, Secondly, Space is NOT a vacuum, the only way to achieve a "vacuum" is to draw all of the air out of a sealed enclosure, Space is lack of/ or possably "negative air pressure".

I must admit, I agree with the time thing though.

This should be a sticky, it's fun and nobody is getting bashed!

 

[J Star]

You're all forgetting the one thing the gun needs to fire at all: Oxygen. It's never been proven that a gun will go off in a vacuum, despite the presence of a built in oxidizer.

I believe this has been discussed to some length on this board, as well as on various physics boards.

 

[jonmerritt]

O2 is not needed for a gun to fire in a non o2 enviroment, that IS why there is an oxidizer! science class, a bullet will fire in a vacume. space is NOT a vacume. And if you did this experiment, you would lose a nice hand gun

 

[Loosedhorse]

Initially, in the first fraction of a microsecond, the muzzle flip will be down, not up.

No. This might be right if the slide traveled without friction. In the first fraction of a microsecond, friction would prevent the slide from moving at all and the recoil spring would initially resist compression (just like the surface of water initially feels much harder to a cannon-baller than it "really is"), and the slide and frame will move as one. So muzzle flip will be "up," as soon as the bullet (or any gases that escape ahead of it) starts to move.

I would expect the gun to spin from the bullet being fired above the center of mass, but absent gravity, no.

No. The muzzle will flip: the pistol retains its center of mass in a weightless environment. (And as has been said by Loomis, as long as there is mass there is gravitational force.)

When the gun in space goes bang, and no one is there, Does it really go BANG?

Definitional question: if by "go BANG", you mean ignites its charge or agitates molecules, then of course it does. If by "goes bang" you mean produces a subjective sensation of sound--well that would depend on an auditorily aware organism being present, and you have specified that there are none.

The falling hammer will impart a small force moving the muzzle downwards, very slowly

No. As the hammer spring forces the hammer "down," so also would it force the gun "up" to meet the hammer. But...

There is NO falling hammer: OP specified "remote primer ignition."

"At the end of the class notes, you will find 20 questions. At the end of the 20 questions, you will find 20 answers. The answers are correct. If you get any other answer, YOU ARE WRONG."--Jack Holladay, MD, MSEE, FACS

 

[RecoilRob]

It certainly HAS been proven, time and again, that a firearm will fire in a no-oxygen environment.

Put your 1911 in the swimming pool and pull the trigger....report back what happens!

 

[rcnixon]

Loomis, I do believe you are right about the hammer and the rest of the gun. The masses and reletive velocities are something to think about.

Sorry, J Star, you are wrong. What about guns (and for that matter, explosives) that fire underwater? There's not much air at "full fathom five". As a matter of fact, solid (and liquid) rockets fire quite well in a (near) vacuum. It's how Yuri Gagarin de-orbited.

 

[Loomis]

Loosedhorse:

You are wrong about friction. Theoretically, there is no friction force without a force normal to the friction face. Where is your force normal to the slide and frame in the first fraction of a microsecond?

 

[Loosedhorse]

I may be wrong--or perhaps just unclear--about what the first "fraction of a microsecond" is, but not about friction: are you saying that the slide initially travels with no friction? If that is so, I was unaware that that was possible--I had always assumed that as soon as a body begins to move (unless suspended in theorectically ideal vacuum and not in contact another body), it encounters friction.

If friction does begin at first slide movement, that friction will impart spin (as well as translational movement) on the frame the moment the slide begins its movement. Additionally, if the spring initially resists compression, then the slide movement will be inhibited as the bullet begins to move, and muzzle flip (upward) and gun translation will begin even before the slide begins to move relative to the frame.

If not, I stand corrected.

 

[Blakenzy]

What would be the velocity of that 230gr. bullet fired in outerspace?

 

[Loomis]

Let me put it this way...

With no "clamping force" between slide and frame, there is no friction. On earth, gravity provides the initial "clamping force". After firing, the muzzle flip provides the "clamping force"...slide is pushed towards frame at the rear, and pulled away from the frame at the front of gun. But even with the friction force present, it is very very small compared to other forces acting on gun.

In space, there is no initial "clamping force, therefore, no initial friction force.

 

[Loomis]

Initial muzzle velocity of bullet relative to gun will be slightly higher in space than on earth. This is because there is no air pressure in front of the bullet to resist bullet forward motion. This difference is very small, however.

But...notice I said "relative to gun". Since the gun accelerates away from the bullet when fired in space, the velocity of the bullet relative to a fixed point will be equal to the value on earth minus the velocity of the gun in space, plus the small bonus from no air pressure in front of the bullet.

 

[Loosedhorse]

Loomis--I disagree: simple metal-on-metal fit (or the viscosity of gun oil--let's assume the 1911 is well cared for, as it ought to be!) provides your missing clamping force that "connects" slide to frame.

(I mean, I know some 1911s have a loose frame to slide fit, but you're proposing so loose a fit that there is no contact at all between slide and frame unless gravity pushes the slide down? Don't think I've encountered that yet!)



But let me sign off for a while, drink some scotch, and more thoroughly consider your argument.

Until later, my best regards, and thanks.

 

[GarandOwner]

It is always entertaining to see what people answer when physics questions are asked (and I found humor in the fact that someone with the name "physics" doesnt understand basic dynamics) Ill try to explain, but physical descriptions are sometimes hard in words without any visual aids anyway, here it goes:

Does the muzzle flip?

yes, the force of the bullet accelerating away from the gun will create a moment, which in turn enacts an angular acceleration on the gun about its center of mass.

Does the gun travel straight back?

No, as the objects rotates, it will "precess" (think of a top or a gyroscope) but the path will be mostly linear

Since there is no resistance, do both the gun and the bullet travel equal distances?

Each will travel until it encounters another body, is slowed by particles in space, or enters the gravity of another object

Does the returning slide push the gun forward?

possibly, but not enough to stop the gun from moving, Here you have two frames of reference, an inertial frame (fixed on the gun) and a universal frame (fixed at some point in space that does not move with the gun) we think of how we perceive things in the universal frame, however trying to do the calculations in this frame will be extremely complicated and far to "messy" that is why we have easy conversions between frames (hurray orbital mechanics class) vector calculations and frame conversions to calculate how much of an effect the moving slide will cause. More than I would want to do from a hypothetical situation with no data

Think about it. When you exert a force off center of mass, what causes it to spin? Gravity. You exert a force in the x, gravity in the y, so the object spins. In space, you exert a force in x, and there is no force in y, so the object just accelerates in x.

This is incorrect, the moment created by the force acting at a certian distance away from the center of mass causes an object to spin. A moment creates an angular acceleration, which would cause the object to spin if it is not constrained. What you are talking about is forces, not moments. While a force in the x direction will cause the gun to move opposite that, if it is not on the center of mass, then it will cause a moment (force x distance from CM) which will cause an angular accleration. This is basic dynamics.

Sum of moments:

Force x distance = I x alpha

Where alpha is the angular acceleration and I is the moment of inertia.

Gravity does not cause rotation, because the force has no moment arm, it acts at the center of mass in most applications.

Theoretically, there is no friction force without a force normal to the friction face

contact force, however slight IS, a force normal to the surface. (normal means perpendicular for anyone who was unclear about that term)

I wont even touch the hammer question, WAAAAAY two many variables with 3 frames of reference which you have to convert between.

 

[saspic]

I wont even touch the hammer question, WAAAAAY two many variables with 3 frames of reference which you have to convert between.

Don't forget the firing pin. If it was a normal 1911, not a "remote primer ignition system"(?), the firing pin would, after ignition, be pushed backwards by the firing pin spring.

Also you will have to stake the grip safety.