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Recoil Gedankenexperiment...

  • 09-09-2010 9:24pm
    #1
    Closed Accounts Posts: 76 ✭✭


    Does the weight of the person using the firearm have a large effect on muzzle velocity ?

    thx


«1

Comments

  • Moderators, Sports Moderators Posts: 28,743 Mod ✭✭✭✭Cass


    I don't mean to be ignorant, but What? :confused:

    Are you sure you worded that question right?

    A persons weight has absolutely NO BEARING on muzzle velocity.
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  • Registered Users, Registered Users 2 Posts: 1,896 ✭✭✭jap gt


    housemap wrote: »
    Does the weight of the person bullet usinged in the firearm have a large effect on muzzle velocity ?

    thx

    maybe thats what he/she meant


  • Closed Accounts Posts: 5,108 ✭✭✭pedroeibar1


    ezridax wrote: »
    I don't mean to be ignorant, but What? :confused:

    Are you sure you worded that question right?

    A persons weight has absolutely NO BEARING on muzzle velocity.

    Yes it does. A heavy person would be a tighter fit in the barrel so there would be a proper seal thus ensuring the projectile would block the gases more efficiently and obtain maximum propulsion!!:D:D
    P


  • Registered Users, Registered Users 2 Posts: 40,038 ✭✭✭✭Sparks


    But they'd mass more and therefore require more energy pedro, so would it even out? :D


  • Moderators, Sports Moderators Posts: 28,743 Mod ✭✭✭✭Cass


    Yes it does. A heavy person would be a tighter fit in the barrel so there would be a proper seal thus ensuring the projectile would block the gases more efficiently and obtain maximum propulsion!!:D:D
    P


    Brilliant :D:D

    As long as it refers to balistics. I thought there was an agenda against fat gits. I would have taken offence. :D
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  • Registered Users, Registered Users 2 Posts: 40,038 ✭✭✭✭Sparks


    ezridax wrote: »
    I thought there was an agenda against fat gits. I would have taken offence. :D
    You would have had to have taken a number.
    And the fat ISSF gits would get first dibs because we wind up wearing spandex.




    And yes, it's as daft-looking as it sounds. :D


  • Closed Accounts Posts: 76 ✭✭housemap


    I was just reading this interesting article here

    http://en.wikipedia.org/wiki/Physics_of_firearms

    This bit mislead me

    Since the mass of the bullet is much less than that of the shooter there is more kinetic energy transferred to the bullet than to the shooter.

    It gave me the impression there is a set amount of kinetic energy that is divided between shooter/firearm and bullet upon discharge depending on the weight of each so that the greater the weight of the shooter the less kinetic energy they gain and the more the bullet gains.

    However I think they meant that there is no total set amount of kinetic energy, that the bullet depending upon its weight will gain a set amount of kenetic energy and muzzle velocity, and so will the shooter/firearm.
    So the bullet will always have muzzle velocity X and the shooter/firearm will have velocity Y which will go up or down depending on their weight (but will not actually result in a velocity in most instances as the energy is absorbed by the shooters body)

    So yea the weight of the shooter has no effect on muzzle velocity,
    thx guys


  • Closed Accounts Posts: 5,108 ✭✭✭pedroeibar1


    Sparks wrote: »
    But they'd mass more and therefore require more energy pedro, so would it even out? :D

    :D:D

    Haven’t really got the time to go the distance on this one, Sparks, but my premise is based on fat, which is more flexible and weighs considerably less than muscle/bone.



    A big arse would be pushed forward by the propellant gases, thereby providing a good flange or seal around the projectile. On exiting the muzzle, the force from the rear on the rear would cease and the fat flange would become more streamlined and thus provide a more aerodynamic shape for the projectile.



    There are other factors, such as the projectile crapping itself at the time of explosion, thereby dampening the propellant, producing a slower burn. However, a longer barrel would (could? ) overcome this. Get my drift?
    P.


  • Closed Accounts Posts: 9,244 ✭✭✭rrpc


    In answer to the OPs question, the answer is yes because heavier people are better at shouting their mouths off, so get a higher muzzle velocity as a consequence. :D


  • Moderators, Sports Moderators Posts: 28,743 Mod ✭✭✭✭Cass


    A big arse would be pushed forward by the propellant gases, thereby providing a good flange or seal around the projectile....................... other factors, such as the projectile crapping itself at the time of explosion, thereby dampening the propellant, producing a slower burn. ..............


    Stop, seriously, i'm p***ing myself here.:D


    Ah, God bless a slow TV night. This is much better.
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  • Registered Users, Registered Users 2 Posts: 5,500 ✭✭✭tac foley


    housemap wrote: »
    Does the weight of the person using the firearm have a large effect on muzzle velocity ?

    thx

    Well, a heavier person may well squeeze the trigger harder, thus making the bullet go a lot faster.

    Actually, I think you'll find that the transfer of proportional kinetic energy from the rifle to the person takes place during the recoil process, and recoil is a function of the mass and velocity of the cartridge plus the propelling gases. Remember that gas has mass, too. A heavier bullet in a larger calibre produces more recoil energy - in other words, the 'kick' from the gun is bigger. If you are built like a leprechaun then you'll feel it more than if you are a lard-ass gossoon.

    All the energy required to send a bullet on its way up the bore is produced by the rapid deflagration of the propellant powder in the cartridge case, and has absolutely nothing to do with the weight of the shooter.

    I respectfully suggest that you read the article until you have the theory firmly emplanted in the ould noddle.

    If lighter people could shoot further then you'd be having ten-year-olds shooting .50cal long-range rifles out to three miles - and getting knocked arse over head with every shot, too. whereas the lard-ass shooting beside them would have his bullet falling out of the sky at a hundred yards.

    tac


  • Registered Users, Registered Users 2 Posts: 1,603 ✭✭✭dCorbus


    Well, based on the "knowledge" i've just gained from reading good ol' wikipedia, i have calculated that my own muzzle velocity is considerably more than IRLConor's, slightly more than rrpc's, about the same as ezridax's, and slightly less than sparks'!:D:D:rolleyes: Itwasn'tme's muzzle velocity has decreased proportionately to his new training regime.:rolleyes: (Or is it all the other way around:confused::D)

    There was me getting a new barrel on my .308 to increase the muzzle velocity, when little did I know that all it would take would be a few extra trips to Mickey D's to supersize me, and not the barrel.

    Figgy should open a burger joint - He'd get more business that way and would increase all our muzzle velocities without any of that messing around with machinery!

    And then there's the new HPS Supersized Half-Pounder triple-decker with extra swiss!


  • Moderators, Sports Moderators Posts: 28,743 Mod ✭✭✭✭Cass


    dCorbus wrote: »
    .......... about the same as ezridax's, ..........!

    HEY! :eek:


    I knew it. Ye're all calling me fat..........................



    .................. i'm not saying its untrue, but no need to be mean about it.:D
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  • Registered Users, Registered Users 2 Posts: 1,603 ✭✭✭dCorbus


    Pots & Kettles, my good man!:P

    :D:rolleyes:


  • Registered Users, Registered Users 2 Posts: 1,603 ✭✭✭dCorbus


    the answer is yes because heavier people are better at shouting their mouths off, so get a higher muzzle velocity as a consequence

    Shouldn't that particular phenomenon be more correctly termed: "Guzzle Verbosity"?

    :D


  • Registered Users, Registered Users 2 Posts: 1,603 ✭✭✭dCorbus


    On exiting the muzzle, the force from the rear on the rear would cease and the fat flange would become more streamlined and thus provide a more aerodynamic shape for the projectile.

    And if the projectile was a bit dim would that then be a: HPBT?
    A Hollow Point Butt Tail?

    :D



    Must......stop......now......

    Good night, seattle!


  • Closed Accounts Posts: 2,616 ✭✭✭FISMA


    The article appears to mostly be concerned with the Law of Conservation of Momentum (LCOM) and Newton's Third Law: action and reaction pairs.

    When fired, the firearm basically has two reactions. First the bullet goes forward and the firearm goes back. Second the bullet twists (say) clockwise and the firearm twists counterclockwise.

    The force ON the person BY the firearm is equal and opposite to the force ON the firearm BY the person - that's Newton's Third Law.

    Also, momentum MUST, I say MUST, be conserverd. The LCOM is more near and dear to a Phyicist's heart than anything, even the Law of Conservation of Energy.

    Anyhow, momentum is conserved. Momentum, p = mv. The massive shooter has a small recoil speed and the fast bullet has a little mass. The masses and speeds balance. Note that in p = mv there are no squared terms so neither speed nor mass dominate.

    Kinetic Energy depends upon mass and speed squared. Thus, when determining KE, speed, really, really matters (get it - really^2) :)

    KE is conserved only in an ellastic collsion, which this is not. This "collision" is inellastic. Collision defined as an energy exchange.

    I think you are trying to find out which bullet would have a greater muzzle velocity:

    (a) Rifle secured in a vice, bolted to a table, bolted to the Earth, and fired.
    (b) Rifle secured in a vice, bolted to a table, on frictionless ice, and fired.

    Kind of like a big guy vs a smaller person shooting a firearm. One gets kicked back more than the other.

    Was this the question?


  • Registered Users, Registered Users 2 Posts: 40,038 ✭✭✭✭Sparks


    Thing is, in this case, the shooter's mass is irrelevant to the frame of reference of the bullet and rifle - the relevant force is between the rear of the chamber and the rear of the bullet, so bench vice or frictionless ice, the bullet will be going at the same speed every time relative to the rifle.

    When the shooter stops the rifle flying back with recoil, he's not accelerating the bullet - he's transferring the rifle's part of the energy from the propellant into the ground.

    So in theory at least, every shot you fire moves the world :D


  • Closed Accounts Posts: 76 ✭✭housemap


    FISMA wrote: »
    The force ON the person BY the firearm is equal and opposite to the force ON the firearm BY the person - that's Newton's Third Law.

    Thats true but thats not what is counter intuitive.

    The force on the bullet (caused by expanding gases after powder burns) is equal to the force on the shooter/firearm (caused by expanding gases after powder burns) , I would imagine this would lead the average person to wonder why if the forces are equal are the effects so different - the shooter just feeling a slight jolt while the object struck by the bullet suffers severe trauma.

    FISMA wrote: »
    I think you are trying to find out which bullet would have a greater muzzle velocity:

    (a) Rifle secured in a vice, bolted to a table, bolted to the Earth, and fired.
    (b) Rifle secured in a vice, bolted to a table, on frictionless ice, and fired.

    Kind of like a big guy vs a smaller person shooting a firearm. One gets kicked back more than the other.

    Was this the question?

    Yes exactly :)


  • Registered Users, Registered Users 2 Posts: 40,038 ✭✭✭✭Sparks


    housemap wrote: »
    I would imagine this would lead the average person to wonder why if the forces are equal are the effects so different - the shooter just feeling a slight jolt while the object struck by the bullet suffers severe trauma.
    Dunno 'bout that - firing a lee enfield feels like trauma to my shoulder :D


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  • Registered Users, Registered Users 2 Posts: 167 ✭✭WallysWorld


    :D:D
    the force from the rear on the rear would cease and the fat flange would become more streamlined and thus provide a more aerodynamic shape for the projectile.

    Ha ha, perhaps appropriately I'm crapping myself here that is one of the best constructed sentences I thought I'd never read!
    I presume the op means Newtons law, equal and opposite forces and all that. So if a fat fella fires a rifle theres more mass opposing the force of the bullet exiting the barrel than if a dude a couple of stone lighter holds and fires the same rifle. It makes sense in that the fat **** provides a greater force to oppose the opposite force of the bullet but in reality I'm sure its actually non existent as far as any practical application.


  • Registered Users, Registered Users 2 Posts: 40,038 ✭✭✭✭Sparks


    Okay, it's a thought experiment, but it's an interesting one...
    if a fat fella fires a rifle theres more mass opposing the force of the bullet exiting the barrel than if a dude a couple of stone lighter holds and fires the same rifle.
    I still don't think that's true. The force on the bullet comes from the gas pressure on the back of the bullet from the propellant burning in the chamber. But that pressure is going to be (for all intents and purposes) even throughout the chamber, and the bullet is not attached to the rifle; so what's happening is that the gas in the middle is pushing on the rifle on one side and the bullet on the other with the same amount of force. Push the rifle and you're not pushing the bullet because it's not connected to the rifle. So it doesn't matter whether you've embedded the rifle butt in a mountain or whether it's on an air hockey table with no friction; the speed of the round relative to the rifle is going to be the same either way. And since we're not talking about pushing the rifle towards the bullet, but either (a) holding it still, or (b) letting the rifle move backwards, you can't even talk about pushing the rifle forwards fast enough to compress the gas behind the round and thus push the bullet indirectly.

    You could measure this - sit the rifle in a bench vise and fire a round and chrony it; then sit the rifle in a batch testing rig that slides backwards easily and fire a round and chrony it. You'd have to fire more than one round, more than likely, to get rid of the minor variations between each round, but I'd bet a danish that the two speeds would be the same.


  • Registered Users, Registered Users 2 Posts: 3,070 ✭✭✭cavan shooter


    Butt:D is the bullet not gone down range (all be it very small distance) by the time recoil is felt.?? ie. the only effects felt on it is friction and gravity


  • Registered Users, Registered Users 2 Posts: 40,038 ✭✭✭✭Sparks


    In human terms cavan, yes (unless you're shooting an old air rifle); in physics terms, you're zooming in to look at the few microseconds between the primer igniting and the round leaving the barrel (after that point, there's no linkage of any kind between round and rifle and so it doesn't matter what happens to the rifle after that from the bullet's point of view).


  • Closed Accounts Posts: 5,108 ✭✭✭pedroeibar1


    Sparks wrote: »
    In human terms cavan, yes (unless you're shooting an old air rifle); in physics terms, you're zooming in to look at the few microseconds between the primer igniting and the round leaving the barrel (after that point, there's no linkage of any kind between round and rifle and so it doesn't matter what happens to the rifle after that from the bullet's point of view).



    No so sure, Sparks, what about barrel flip?
    Also, there is friction .....and torque. While the bullet technically is not fixed to the barrel wall, it is in contact with it to a limited extent, thus there is some friction. (Is that not why air gun users have oil?) When the propellant ignites there is a torque element – for every action there is an equal and opposite reaction – hence recoil and some torque in a grooved barrel. The mass of the projectile and the mass of the gun determine recoil – e.g. WW Greener’s rule of 98. Also, in a SxS, the recoil will throw the right barrel to the right and the left barrel to the left since the axes of the barrels are respectively situated to the right or left of the centre of gravity, thus influencing recoil.


    It’s a wonder nobody brought up inertia...........
    I did NOT start this thread!

    I’m leaving now... ;)
    P


  • Closed Accounts Posts: 8,590 ✭✭✭Tackleberrywho


    http://www.rticl.com/html/industry.html

    A little light reading.

    In regards to shooting, I know two guys who shoot the same rifle, both shoot as well as each other, one is a good 5stone heavier than the other guy.

    When I was young I was skinny 11 stone, my grouping was reasonable. Now it is better and I am over 14stone.

    I attribute this to practice,practice,practice............not being a fat cnut;)


  • Registered Users, Registered Users 2 Posts: 40,038 ✭✭✭✭Sparks


    No so sure, Sparks, what about barrel flip?
    Doesn't affect the speed of the bullet after it leaves the barrel. And really, doesn't affect the speed at all, just the direction.
    Also, there is friction .....and torque. While the bullet technically is not fixed to the barrel wall, it is in contact with it to a limited extent, thus there is some friction. (Is that not why air gun users have oil?) When the propellant ignites there is a torque element – for every action there is an equal and opposite reaction – hence recoil and some torque in a grooved barrel. The mass of the projectile and the mass of the gun determine recoil – e.g. WW Greener’s rule of 98. Also, in a SxS, the recoil will throw the right barrel to the right and the left barrel to the left since the axes of the barrels are respectively situated to the right or left of the centre of gravity, thus influencing recoil.

    It’s a wonder nobody brought up inertia...........
    I did NOT start this thread!

    I’m leaving now... ;)

    Oh no you don't :D
    And yes, all those things are correct, but they're not affected by whether the recoil is absorbed by a shooter/bench vice/whatever or whether it's just left knock the rifle around.
    Trick is, look at things from inside the rifle, considering only the inside of the chamber, the gas and the bullet. In that frame of reference, the speed of the bullet is constant. If the entire frame (ie the entire rifle) is sent flying around by the recoil, it'll affect where the barrel points but not the speed of the bullet relative to the barrel.


  • Closed Accounts Posts: 8,590 ✭✭✭Tackleberrywho


    Sparks wrote: »
    Doesn't affect the speed of the bullet after it leaves the barrel. And really, doesn't affect the speed at all, just the direction.



    Oh no you don't :D
    And yes, all those things are correct, but they're not affected by whether the recoil is absorbed by a shooter/bench vice/whatever or whether it's just left knock the rifle around.
    Trick is, look at things from inside the rifle, considering only the inside of the chamber, the gas and the bullet. In that frame of reference, the speed of the bullet is constant. If the entire frame (ie the entire rifle) is sent flying around by the recoil, it'll affect where the barrel points but not the speed of the bullet relative to the barrel.

    The speed of the bullet is not constant it is a vector quantity hence termed in velocity. speed is a scaler quantity with no magnitude ;)


  • Registered Users, Registered Users 2 Posts: 40,038 ✭✭✭✭Sparks


    Tack;
    (1) constancy is not connected to the dimensionality of the property being measured, but to whether or not it's changing;

    (2) you just said that speed is a vector hence it's called velocity. It isn't. We're not talking about velocity at all here, we're talking about speed, the scalar measurement.


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  • Registered Users, Registered Users 2 Posts: 11,393 ✭✭✭✭Vegeta


    Sparks wrote: »
    the speed of the bullet relative to the barrel.

    Yes it's all relative.

    I agree Sparks that relative to the chamber and therefore barrel, it does not matter what way the gun is being held. The round will travel the same speed

    Consider though the speed relative to the target (chronograph at fixed point near target). If the chamber is moving away from the target at time of firing (say on the back of a very fast truck driving directly away from the target) and the bullet speed is relative to the chamber then it certainly makes sense that the bullet will arrive on target at a lower speed than a setup where the chamber does not move away from the target.

    Now from all the high speed shots or super slow motion shots I've seen, it always seems that the round has left firearm before recoil (a force driving the chamber away from the target) takes effect. So I doubt it effects speed in a meaningful way


  • Registered Users, Registered Users 2 Posts: 854 ✭✭✭firefly08


    So it doesn't matter whether you've embedded the rifle butt in a mountain or whether it's on an air hockey table with no friction

    So where does the force that would normally push the gun backwards go? Is it absorbed by the earth? I don't think so- the force that would normally push out in every other direction is not absorbed by the barrel. If it was the barrel would do no good. Instead what happens is that the gas channelled because it is prevented in going outwards, perpendicular to the bore - it can only push in 2 directions; forwards, pushing the bullet out, and backwards, pushing the rifle back. Surely by reducing the places the gas can go even further, you will increase the pressure? I doubt you could measure the difference in speed, but I think there has to be a difference.

    Look at it this way: increasing the mass of the bullet would increase the energy imparted to the shooter. Why should it not work the other way around?


  • Registered Users, Registered Users 2 Posts: 40,038 ✭✭✭✭Sparks


    firefly08 wrote: »
    So where does the force that would normally push the gun backwards go? Is it absorbed by the earth?
    Yes. Same as every other time you fire the rifle. I mean, if you grab the rifle, how do you think you stop the rifle moving backwards? By pushing against the planet. :)

    I don't think so- the force that would normally push out in every other direction is not absorbed by the barrel. If it was the barrel would do no good. Instead what happens is that the gas channelled because it is prevented in going outwards, perpendicular to the bore - it can only push in 2 directions; forwards, pushing the bullet out, and backwards, pushing the rifle back. Surely by reducing the places the gas can go even further, you will increase the pressure? I doubt you could measure the difference in speed, but I think there has to be a difference.
    Except that by preventing the rifle moving under recoil you do absolutely nothing to the gas pressure. It's pushing out in all directions at once and equally (let's leave aside turbulence and gas fluid pressure waves just for the moment :D ). The sides of the chamber all resist through the tensile strength of the steel, as does the back of the chamber; the only avenue left is via the barrel, pushing (and pushing around) the bullet in the process. Recoil's irrelevant to this: think about it, if the bullet wasn't in the rifle, would you still get recoil? Yes, and the same amount; which means that the force on the bullet is going to be the same as well.
    Look at it this way: increasing the mass of the bullet would increase the energy imparted to the shooter. Why should it not work the other way around?
    Actually, it wouldn't; increasing the mass of the bullet would lead to a decrease in speed of the bullet; that's why we measure muzzle energy not muzzle velocity when deciding what the firearm/not-a-firearm cutoff is for airguns, so that you can't go from a toy to a firearm by loading a heavier pellet.


  • Registered Users, Registered Users 2 Posts: 854 ✭✭✭firefly08


    if the bullet wasn't in the rifle, would you still get recoil? Yes, and the same amount; which means that the force on the bullet is going to be the same as well.

    Are you sure? I have never fired a blank round from a gun, so I admit I'm guessing here - but surely the recoil must be significantly less when there's no bullet? When the gas starts to expand, it meets the bullet; the bullet pushes back - isn't that what causes the recoil?


  • Registered Users, Registered Users 2 Posts: 40,038 ✭✭✭✭Sparks


    No.
    The recoil comes from the gas, not the bullet (the sole force the bullet can put on the gun would be via friction with the lands and that'd drag the gun forwards, not push it back).
    Think of the gas cloud behind the bullet; you can model the force as originating in the centre of the cloud.
    It's like a rocket ship, basicly; you don't need something outside the rocket for it to push on in order for the rocket to work.


  • Closed Accounts Posts: 5,108 ✭✭✭pedroeibar1


    Vegeta wrote: »
    Yes it's all relative.
    :D:D

    Vegeta wrote: »
    Consider though the speed relative to the target (chronograph at fixed point near target). If the chamber is moving away from the target at time of firing (say on the back of a very fast truck driving directly away from the target) and the bullet speed is relative to the chamber then it certainly makes sense that the bullet will arrive on target at a lower speed than a setup where the chamber does not move away from the target.

    Now from all the high speed shots or super slow motion shots I've seen, it always seems that the round has left firearm before recoil (a force driving the chamber away from the target) takes effect. So I doubt it effects speed in a meaningful way

    Sort of contradicting yourself??
    but.....



    Consider a flatbed truck travelling at a constant 100kph on the trailer of which a ball is dropped from a position behind the cab. It does not fall onto the road behind the trailer because the ball has inertia, i.e. the ball is moving at the same speed as the truck. (Inertia being the resistance of any physical object to a change in its state of motion or rest.)* Apply the same logic to a bullet; the ignition speed of the propellant is so fast the bullet’s speed relative to the breech is zero. So there will be no material difference.


    However, I do admit that the bullets path, like a ball being dropped off the trailer i.e. outside, will be subject to the much greater forces of friction and gravity. That path can best be described as a load of parabolics.


    *a feature common/well-known to some posters on these Boards



    I reall have to do some work...............
    P.


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  • Registered Users, Registered Users 2 Posts: 854 ✭✭✭firefly08


    you don't need something outside the rocket for it to push on in order for the rocket to work.

    So you are saying that restricting where the gas can go (i.e. having something for it to push against) has no effect on the force it applies to the projectile?


  • Registered Users, Registered Users 2 Posts: 40,038 ✭✭✭✭Sparks


    Well, it does - in that if the projectile isn't in the barrel in the first place, there'll be no force applied to it :D
    What I'm saying is that the force applied to the rifle is the same as the force applied to the bullet regardless of whether or not the bullet is there.

    Look at it on an atomic level. A gas is just atoms flying about. The number of atoms per unit volume is the pressure. So right after the propellant burn, there are propellant atoms flying all over the place behind the round, bouncing off the walls of the chamber and the back of the bullet. Every time one of them bounces, it imparts energy to the surface it bounces off.

    Ones that bounce off the back of the bullet push the bullet; ones that bounce off the back of the chamber create the recoil. But if there's no bullet, you still get atoms bouncing off the rear of the chamber.

    Hmm. But you wouldn't get so many bounces in a given unit of time, so yes, you'd have less recoil if you'd an open chamber (not thinking about the wad you normally get in a blank, for the moment). But that still doesn't mean that the bullet will get less or more force if the rifle is allowed to recoil or not; the number of bounces the back of the bullet gets is dependant on the speed of the bullet relative to the barrel only; once the bullet leaves the barrel, no more bounces.


  • Closed Accounts Posts: 8,590 ✭✭✭Tackleberrywho


    Sparks wrote: »
    Tack;
    (1) constancy is not connected to the dimensionality of the property being measured, but to whether or not it's changing;

    (2) you just said that speed is a vector hence it's called velocity. It isn't. We're not talking about velocity at all here, we're talking about speed, the scalar measurement.

    We are talking about velocity with acceleration and retardation. it increases in Velocity the longer the barrel. Hence the term Muzzle velocity **not Speed**

    Speed is a constant
    Velocity is not constant.

    An object traveling in space "in theory" is traveling at speed. Although space is curved**

    A projectile travelling down a barrel is traveling faster the further down the barrel it can go up to a certain point depending on calibre and powder.

    it then is retarding from then on.

    "high velocity ammo" not High speed ammo. Muzzle Velocity measured in metres or feet per second.

    Weight is also the wrong term for bullets. they are of a mass, which has to be multiplied by gravity to give force in newtons.

    if you want to be technical, you have to be very technical.


  • Closed Accounts Posts: 2,616 ✭✭✭FISMA


    I'll have to get out the auld books. Sparks and Vegeta appear to be saying that the relative speed between the rifle and the bullet is the same in either case, correct?

    This is most definitely true for an elastic head-on one dimensional collision, the relative speeds of two particles after the collision has the same magnitude as before and does not depend upon the masses.

    I am willing to allow the "collision" herein to be safely assumed as head on and one dimensional, even though there is rotational motion. What concerns me more is that our collision is inellastic and not elastic. I'll have to double check to see if the above paragraph applies to inellastic collisions. The case that we have I colloquially call an un-inellastic collision.:)

    How about a little Gedankenexperiment?

    In the middle of a large frozen pond, with perfectly frictionless ice, there is the stump of a tree, stuck in to the ground at Pt A. At pt B, there is a stump resting on top of the ice, not stuck to the ground. All things equal, except for the way in which the stumps and anchored.

    100 yards downrange is a finish line, stuck in to the Earth, like the stump at A.

    Timmy is at A and Jimmy at B. Timmy and Jimmy are going to push off of the stumps and we are to determine the winner, by the one who crosses the finish line first.

    The starter pistol fires and both Timmy and Jimmy (initially connected to the stump) push off. Who wins the race?

    I think this is like the situation posted by the OP.

    The one who wins the race is the faster bullet, as judged by the target - the Earth bound reference frame.

    I am confident that we'll agree that Timmy wins the race. I believe that both Timmy and Jimmy have the same relative velocity with respect to their starting stumps. Although, again, I will have to double check as this is an inellastic collision.

    Thus, in theory, for this situation, there is a difference, however, I doubt that in practice using a chrono, one could consistently demonstrate an appreciable difference based upon the mass of the shooter.

    So to the OP, No, the mass/weight of the shooter does not have a large effect on the muzzle velocity.

    I'll state that the mass of the shooter has a negligible effect on the muzzle velocity of the bullet as measure in an Earth bound reference frame at the muzzle.


  • Registered Users, Registered Users 2 Posts: 11,393 ✭✭✭✭Vegeta


    Sort of contradicting yourself??
    but.....

    Not at all actually, in one case the gun is being fired from a fast moving vehicle.

    The other case the gun is being held by the shooter which is usually pretty much static relative to the target.


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  • Registered Users, Registered Users 2 Posts: 11,393 ✭✭✭✭Vegeta


    Check this video out at like 3 minutes 20 seconds



  • Registered Users, Registered Users 2 Posts: 854 ✭✭✭firefly08


    The ice race example makes sense to me.

    Look at it another way:

    Suppose the bullet in the rifle is anchored to the earth somehow (let's say it extends out the barrel and is attached to a wall or whatever). Assume the barrel is indestructible. When the shooter fires, what will happen? Surely he will be thrown backwards, off his feet. Doesn't this show that the force is divided between the bullet and the shooter in proportion to the resistance they each offer (just like electricity)?


  • Closed Accounts Posts: 5,108 ✭✭✭pedroeibar1


    Vegeta wrote: »
    Check this video out at like 3 minutes 20 seconds

    Sorry Veg, I'm on dongle and outside BB area - 21st C Ireland:mad:
    P.


  • Registered Users, Registered Users 2 Posts: 40,038 ✭✭✭✭Sparks


    We are talking about velocity with acceleration and retardation. it increases in Velocity the longer the barrel. Hence the term Muzzle velocity **not Speed**

    Speed is a constant
    Velocity is not constant.
    Tack, that's simply all wrong.
    Speed can be constant or can vary. Velocity can be constant or can vary. And we are focussed on the speed of the projectile in this case because its direction is constrained by the barrel and we're uninterested in it after it leaves the barrel.
    If you don't keep the basics of problems like these clear in your head, they just fall apart.
    "high velocity ammo" not High speed ammo. Muzzle Velocity measured in metres or feet per second.
    "velocity" in those cases is a marketing term, nothing more.
    Velocity in the physics sense (the vector quantity) cannot be simply measured in metres or feet per second, by definition.
    Weight is also the wrong term for bullets. they are of a mass, which has to be multiplied by gravity to give force in newtons.
    Indeed, but unless you regularly shoot outside of a gravitational field, it's a moot point; and has nothing to do with this thought experiment anyway.
    if you want to be technical, you have to be very technical.
    You also have to be correct...


  • Registered Users, Registered Users 2 Posts: 40,038 ✭✭✭✭Sparks


    firefly08 wrote: »
    Doesn't this show that the force is divided between the bullet and the shooter in proportion to the resistance they each offer (just like electricity)?
    No. It would just show (if it happened at all) that containing high pressure gas is difficult. If the force really was divided like that, rockets wouldn't work in space because there'd be nothing for them to push against.


  • Registered Users, Registered Users 2 Posts: 854 ✭✭✭firefly08


    If the force really was divided like that, rockets wouldn't work in space because there'd be nothing for them to push against.

    No, if what I'm suggesting is true, rockets would not work as well in space as they do in air. Equally, they would not work as well in thin air as they would in dense air. I believe this is actually the case.

    Otherwise, I'd be suggesting that an explosion cannot move a bullet unless it's in a barrel. Of course it can; but it can move it a hell of a lot faster if it's in a barrel. Why? Because the gas is forced to expand in the direction of whatever will move. The wall of the barrel will not move; therefore all the force that would otherwise push in that direction must now go somewhere else. It is not simply absorbed by the barrel - it is vectored elsewhere. Why should it be different for the force that would push the rifle back if it could? If the rifle will not move, that force will be vectored towards something that will - the bullet.

    Another thought experiment: let's say we have a barrel and a special round - this cartridge has a bullet sticking out of each end - they are identical. The propellant is between the two bullets and the primer is buried away in the centre. Don't worry about how we ignite it for now - just assume we can. Put this round in the middle of our symmetrical, non-tapered barrel and fire it. Obviously each bullet will travel the same distance, and at the same speed.

    Now we try again, but this time we coat one of the bullets with heat resistant ,unbreakable glue, so that bullet cannot move once it's in place in the barrel. We fix the barrel to the very earth, so it's not going anywhere either. Now when we fire the round, will the bullet that can move go faster and farther than the last time? Yes! It will because there is nowhere else for the energy to go. To suggest that the resistance offered by the blockage in the barrel doesn't affect the energy imparted to the moving bullet is the same thing as saying the barrel itself has no such effect.


  • Registered Users, Registered Users 2 Posts: 40,038 ✭✭✭✭Sparks


    firefly08 wrote: »
    No, if what I'm suggesting is true, rockets would not work as well in space as they do in air. Equally, they would not work as well in thin air as they would in dense air. I believe this is actually the case.
    NASA disagrees:
    ...rockets actually work better in space than they do in air. As the exhaust gas leaves the rocket engine it must push away the surrounding air; this uses up some of the energy of the rocket. In space, the exhaust gases can escape freely.
    Otherwise, I'd be suggesting that an explosion cannot move a bullet unless it's in a barrel. Of course it can; but it can move it a hell of a lot faster if it's in a barrel. Why? Because the gas is forced to expand in the direction of whatever will move. The wall of the barrel will not move; therefore all the force that would otherwise push in that direction must now go somewhere else. It is not simply absorbed by the barrel - it is vectored elsewhere. Why should it be different for the force that would push the rifle back if it could? If the rifle will not move, that force will be vectored towards something that will - the bullet.
    It's different because the gas is trying to escape from the chamber, and is pushing the bullet out of the way to do it. That's the motive force involved; the pressure on the rear of the chamber doesn't affect the speed of the bullet any more than the pressure on the side of the chamber.
    Another thought experiment: ... Now we try again, but this time we coat one of the bullets with heat resistant ,unbreakable glue, so that bullet cannot move once it's in place in the barrel. We fix the barrel to the very earth, so it's not going anywhere either. Now when we fire the round, will the bullet that can move go faster and farther than the last time? Yes! It will because there is nowhere else for the energy to go.
    *ahem* Actually, there is.
    I'm not saying you're going to spin the Earth very much faster, you understand, but that's where the energy is dumped when you absorb the recoil normally anyway, unless you're exempt from Newton's first law...


  • Registered Users, Registered Users 2 Posts: 854 ✭✭✭firefly08


    NASA disagrees

    NASA SCHMASA :p

    Seriously though, fair enough...I can't argue with that. I still don't really understand, but it wouldn't be the first time...:)


  • Closed Accounts Posts: 2,616 ✭✭✭FISMA


    When it comes to Rockets, true they are happy in Space. However, since there's no oxygen to cause combustion, you have to bring it with you - which is desperately expensive.

    At some point you're chasing your tail. You have to bring like oxygen to combust the fuel. But now you need more fuel, to carry that oxygen. But then, you need more fuel, to accelerate the fuel to Mach 20 something... You get the idea. I think it costs $10,000 to get a gallon of water into low earth orbit.

    Anyhow, it's best to say accelerate in Physics. The "m" word - move, is a bad word in Physics. Since all motion is relative, all Physics cares about is whether or not you are accelerating.

    Anywho...

    Here's a simple image
    ch05s08_sup_01.gif

    When the fuel ignites it expels gasses for propulsion. Remember, that objects accelerate in the direction of the unbalanced Force.

    There are Forces everywhere inside of the bell. Up and down Forces pretty much cancel out. In the diagram above, the gasses push on the left hand side of the bell/motor/whatever it is called. However, the gasses that go out into space do not push on anything. Thus, the LHS force is unbalanced and the rocket accelerates to the left. :) Cool huh?


  • Closed Accounts Posts: 8,590 ✭✭✭Tackleberrywho


    FISMA wrote: »
    When it comes to Rockets, true they are happy in Space. However, since there's no oxygen to cause combustion, you have to bring it with you - which is desperately expensive.

    At some point you're chasing your tail. You have to bring like oxygen to combust the fuel. But now you need more fuel, to carry that oxygen. But then, you need more fuel, to accelerate the fuel to Mach 20 something... You get the idea. I think it costs $10,000 to get a gallon of water into low earth orbit.

    Anyhow, it's best to say accelerate in Physics. The "m" word - move, is a bad word in Physics. Since all motion is relative, all Physics cares about is whether or not you are accelerating.

    Anywho...



    When the fuel ignites it expels gasses for propulsion. Remember, that objects accelerate in the direction of the unbalanced Force.

    There are Forces everywhere inside of the bell. Up and down Forces pretty much cancel out. In the diagram above, the gasses push on the left hand side of the bell/motor/whatever it is called. However, the gasses that go out into space do not push on anything. Thus, the LHS force is unbalanced and the rocket accelerates to the left. :) Cool huh?
    I always was very interested in rockets and propulsion
    so can we now state that SPEED is not the correct word and Velocity is :D

    And that a round is accelerating in a barrel until it is retarding & is a vector Quantity as it has magnitude

    This has to be the weirdest thread in a long time :)


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