http://upload.wikimedia.org/wikipedia/en/8/8e/SurfaceTensionHLS.jpg

Remember this gun? I miss this gun. It was the best gun in the game! It 
looks *awesom*, it's very deadly, it's very precise, it has a huge 
range, and you can charge it up to deliver hits that can take down just 
about anything. (If you don't miss!)

Mmm... I wonder if I could model it with POV-Ray...?

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Orchid XP v7 wrote:
> range, and you can charge it up to deliver hits that can take down just 
> about anything. (If you don't miss!)

You forgot "It shoots through walls", altho I must admit I never really 
learned to take advantage of that feature, given the difficulty of 
*aiming* thru walls.

-- 
   Darren New / San Diego, CA, USA (PST)
     Remember the good old days, when we
     used to complain about cryptography
     being export-restricted?

Post a reply to this message

Darren New wrote:
> Orchid XP v7 wrote:
>> range, and you can charge it up to deliver hits that can take down 
>> just about anything. (If you don't miss!)
> 
> You forgot "It shoots through walls", altho I must admit I never really 
> learned to take advantage of that feature, given the difficulty of 
> *aiming* thru walls.

That's news to me...

I know it shoots round corners tho. ;-)

Post a reply to this message

On Sun, 21 Oct 2007 08:40:06 -0700, Darren New wrote:

> You forgot "It shoots through walls", altho I must admit I never really
> learned to take advantage of that feature, given the difficulty of
> *aiming* thru walls.

I liked the approach taken in Perfect Dark with the gun that could do 
that - there was a sort of "X-Ray view" that could be used.

It took a little practice to figure out how to use it, but it worked very 
nicely once you got the hang of it.

Jim

Post a reply to this message

Jim Henderson wrote:

>> You forgot "It shoots through walls", altho I must admit I never really
>> learned to take advantage of that feature, given the difficulty of
>> *aiming* thru walls.
> 
> I liked the approach taken in Perfect Dark with the gun that could do 
> that - there was a sort of "X-Ray view" that could be used.
> 
> It took a little practice to figure out how to use it, but it worked very 
> nicely once you got the hang of it.

I'm reminded of that film that came out a while ago. ("True Lies"?) The 
guy zooms in with an X-ray scope, where he can see the target's heart 
beating and everything... but when he pulls the trigger, the gun blows 
half the building away. I mean, dude, did you *need* to aim the thing??

Post a reply to this message

On Sun, 21 Oct 2007 20:40:09 +0100, Orchid XP v7 wrote:

> Jim Henderson wrote:
> 
>>> You forgot "It shoots through walls", altho I must admit I never
>>> really learned to take advantage of that feature, given the difficulty
>>> of *aiming* thru walls.
>> 
>> I liked the approach taken in Perfect Dark with the gun that could do
>> that - there was a sort of "X-Ray view" that could be used.
>> 
>> It took a little practice to figure out how to use it, but it worked
>> very nicely once you got the hang of it.
> 
> I'm reminded of that film that came out a while ago. ("True Lies"?) The
> guy zooms in with an X-ray scope, where he can see the target's heart
> beating and everything... but when he pulls the trigger, the gun blows
> half the building away. I mean, dude, did you *need* to aim the thing??

I'm wondering if it wasn't Minority Report....

Jim

Post a reply to this message

Le 22.10.2007 04:17, Jim Henderson nous fit lire :
> On Sun, 21 Oct 2007 20:40:09 +0100, Orchid XP v7 wrote:
>> I'm reminded of that film that came out a while ago. ("True Lies"?) The
>> guy zooms in with an X-ray scope, where he can see the target's heart
>> beating and everything... but when he pulls the trigger, the gun blows
>> half the building away. I mean, dude, did you *need* to aim the thing??
> 
> I'm wondering if it wasn't Minority Report....

Nope, the movie name in french was "L'effaceur", "Eraser" in english.
The projectile was a very fine needle (and it fires a lot of them),
spinning along the fireline, propels by a strong magnetic
accelerator (the gun).
The visual was not X-Ray, but ultrasound and detects the
surface-change of density (reflection anyone ?).

-- 
The superior man understands what is right;
the inferior man understands what will sell.
-- Confucius

Post a reply to this message

And lo on Sun, 21 Oct 2007 20:15:39 +0100, Jim Henderson  
<nos### [at] nospamcom> did spake, saying:

> On Sun, 21 Oct 2007 08:40:06 -0700, Darren New wrote:
>
>> You forgot "It shoots through walls", altho I must admit I never really
>> learned to take advantage of that feature, given the difficulty of
>> *aiming* thru walls.
>
> I liked the approach taken in Perfect Dark with the gun that could do
> that - there was a sort of "X-Ray view" that could be used.
>
> It took a little practice to figure out how to use it, but it worked very
> nicely once you got the hang of it.

Red Faction 1 & 2 had an thermal vision rail gun which was very cool;  
one-shot kill, but slow to reload if you missed. Oh and some of the bad  
guys had them too ouch.

-- 
Phil Cook

--
I once tried to be apathetic, but I just couldn't be bothered
http://flipc.blogspot.com

Post a reply to this message

Phil Cook wrote:
> Red Faction 1 & 2 had an thermal vision rail gun which was very cool; 

Or the cursed Celtic Scythe that had the mode it would suck up the 
life-force from whoever's limbs you chopped off with it.  *Very* slow to 
"reload" as you had to wait for it to finish sucking up the hit points, 
but useful if you knew only one enemy was near.

Or the Invoke spell, that either brings (some types of) dead enemies 
back to life to fight for you, or causes (some types of) live enemies to 
commit suicide.  Just don't use it on the enemies with the dynamite, 
unless you have somewhere to run to very quickly.

-- 
   Darren New / San Diego, CA, USA (PST)
     Remember the good old days, when we
     used to complain about cryptography
     being export-restricted?

Post a reply to this message

On Mon, 22 Oct 2007 08:00:38 +0200, Le Forgeron wrote:

> Le 22.10.2007 04:17, Jim Henderson nous fit lire :
>> On Sun, 21 Oct 2007 20:40:09 +0100, Orchid XP v7 wrote:
>>> I'm reminded of that film that came out a while ago. ("True Lies"?)
>>> The guy zooms in with an X-ray scope, where he can see the target's
>>> heart beating and everything... but when he pulls the trigger, the gun
>>> blows half the building away. I mean, dude, did you *need* to aim the
>>> thing??
>> 
>> I'm wondering if it wasn't Minority Report....
> 
> Nope, the movie name in french was "L'effaceur", "Eraser" in english.
> The projectile was a very fine needle (and it fires a lot of them),
> spinning along the fireline, propels by a strong magnetic accelerator
> (the gun).
> The visual was not X-Ray, but ultrasound and detects the surface-change
> of density (reflection anyone ?).

Ah yes, that's the one. :-)

Jim

Post a reply to this message

Le Forgeron wrote:

>> I'm wondering if it wasn't Minority Report....

No, it wasn't.

> Nope, the movie name in french was "L'effaceur", "Eraser" in english.

Ah, yeah, I thought it might be. I can never remember which was which...

Post a reply to this message

Orchid XP v7 wrote:

> Mmm... I wonder if I could model it with POV-Ray...?

...no, I can't.

Post a reply to this message

And lo on Mon, 22 Oct 2007 15:34:58 +0100, Darren New <dne### [at] sanrrcom>  
did spake, saying:

> Phil Cook wrote:
>> Red Faction 1 & 2 had an thermal vision rail gun which was very cool;
>
> Or the cursed Celtic Scythe that had the mode it would suck up the  
> life-force from whoever's limbs you chopped off with it.  *Very* slow to  
> "reload" as you had to wait for it to finish sucking up the hit points,  
> but useful if you knew only one enemy was near.
>
> Or the Invoke spell, that either brings (some types of) dead enemies  
> back to life to fight for you, or causes (some types of) live enemies to  
> commit suicide.  Just don't use it on the enemies with the dynamite,  
> unless you have somewhere to run to very quickly.

Clive Barker's "Undying" for those wondering. I'm looking forward to  
"Jericho" now I've got something that'll play it. Oh and yeah I did like  
Invoke.

-- 
Phil Cook

--
I once tried to be apathetic, but I just couldn't be bothered
http://flipc.blogspot.com

Post a reply to this message

Orchid XP v7 wrote:
> Le Forgeron wrote:
> 
>>> I'm wondering if it wasn't Minority Report....
> 
> No, it wasn't.
> 
>> Nope, the movie name in french was "L'effaceur", "Eraser" in english.
> 
> Ah, yeah, I thought it might be. I can never remember which was which...

Eraser is a ridiculous film in many ways, and although the basic premise 
for the gun is a real one, I'm not too convinced by its high-tec 
sighting software or the dubious claim that it can fire projectiles at 
near lightspeed (especially when you can see them moving onscreen when 
they do fire). It does have one of the Governator's 'best' crap 
one-liners, however - during a gunfight at a zoo they unwittingly 
release a large crocodile, which Arnie then dispatches with the line 
"You're lugguge!"

Post a reply to this message

Bill Pragnell wrote:
> although the basic premise for the gun is a real one, 

Sure. You try holding a weapon that fires something at relativistic speeds.

If you want a realistic treatment, read "A Boy And His Tank."  Anyone 
outside the armored vehicles within about 300 meters was toast.

>I'm not too convinced by its high-tec 
> sighting software 

No.

> or the dubious claim that it can fire projectiles at near lightspeed 

That's what a railgun is for.

>(especially when you can see them moving onscreen when 
> they do fire). 

You're only seeing the shockwave. ;-)


-- 
   Darren New / San Diego, CA, USA (PST)
     Remember the good old days, when we
     used to complain about cryptography
     being export-restricted?

Post a reply to this message

Darren New wrote:

>> although the basic premise for the gun is a real one, 
> 
> Sure. You try holding a weapon that fires something at relativistic speeds.
> 
> If you want a realistic treatment, read "A Boy And His Tank."  Anyone 
> outside the armored vehicles within about 300 meters was toast.

I read somewhere that if you were to fire a "bullet" at near-light 
speeds, it would be more like bein irradiated with "lead radiation" than 
being hit by a solid object...

But anyway, even without relativity, the recoil would be absurd.

>> or the dubious claim that it can fire projectiles at near lightspeed 
> 
> That's what a railgun is for.

Well... technically a railgun (not to be confused with a coilgun) fires 
projectiles using electrical propolsion. There's nothing in the 
definition about how fast. ;-)

Post a reply to this message

Orchid XP v7 wrote:
>> If you want a realistic treatment, read "A Boy And His Tank."  Anyone 
>> outside the armored vehicles within about 300 meters was toast.
> 
> I read somewhere that if you were to fire a "bullet" at near-light 
> speeds, it would be more like bein irradiated with "lead radiation" than 
> being hit by a solid object...

Well, in an atmosphere, it would be like being hit by an explosion, as 
you pile up all the air in front of it. Plus, don't forget all that nice 
gamma-burst radiation. (The railguns in the story actually had to fire 
for a few thousand rounds to punch a hole in the atmosphere so the 
needles wouldn't just vaporize.)

> But anyway, even without relativity, the recoil would be absurd.

Yep. If it can go thru a concrete wall coming out the front, the stock 
can certainly break your shoulder. I mean, the big guns on a battle ship 
will roll the ship in the water, and there's a serious problem with 
modern tanks getting rolled over if they're traveling fast when they 
fire a shell a couple miles, even if it's only a sabot.

> Well... technically a railgun (not to be confused with a coilgun) fires 
> projectiles using electrical propolsion. There's nothing in the 
> definition about how fast. ;-)

True. But to get the electrical propultion to work, the projectile needs 
to be pretty small, which means it needs to go pretty fast. Otherwise 
it's more of a thrower than a firearm. :-)

-- 
   Darren New / San Diego, CA, USA (PST)
     Remember the good old days, when we
     used to complain about cryptography
     being export-restricted?

Post a reply to this message

Darren New wrote:
> 
> You forgot "It shoots through walls", altho I must admit I never really 
> learned to take advantage of that feature, given the difficulty of 
> *aiming* thru walls.
> 

I found that once you learned a map really well, this actually became 
reasonably easy to do, particularly since I think the gun has a bit of 
spray after it goes through a wall.  Once you learned an area well, 
you'd know things like:

- Ok, they just went through that door, so if they run in the normal 
pattern they''l be coming behind this point in the wall/floor in about a 
second and a half.

- I just heard an elevator, and there's only two of those in the level, 
so I'll quickly fire off a shot through the wall of the room adjacent to 
one of them.

It actually got to the point when my friends and I learned that we 
needed to do things like press elevators and not get on them, or run 
around corners, stop, wait for the tau cannon blast or grenade through 
the window, then continue.

I also liked the use of the tau cannon for propelling yourself through 
the air at crazy speeds.

Post a reply to this message

> Well, in an atmosphere, it would be like being hit by an explosion, as you 
> pile up all the air in front of it.

Wouldn't something going that fast vaporize immediately when it hit the air 
going that fast?  Doesn't stuff that going only a fraction of that speed 
burn up in the outer atmosphere?

> Plus, don't forget all that nice gamma-burst radiation. (The railguns in 
> the story actually had to fire for a few thousand rounds to punch a hole 
> in the atmosphere so the needles wouldn't just vaporize.)

Ah yes, ok :-)

>> Well... technically a railgun (not to be confused with a coilgun) fires 
>> projectiles using electrical propolsion. There's nothing in the 
>> definition about how fast. ;-)
>
> True. But to get the electrical propultion to work, the projectile needs 
> to be pretty small, which means it needs to go pretty fast. Otherwise it's 
> more of a thrower than a firearm. :-)

In one of our lectures at university the dude had this rail-gun.  It was 
about 2 metres long and plugged into the 420V 3-phase power supply.  He 
loaded it with a brass (I think) solid lump of metal that was in a pointy 
bullet shape.  It wasn't small, about 10cm diameter and 30cm long.  When he 
flicked the switch it punched through (and got stuck in) a big bit of wood 
just off the end of the bench he was using.  Rig up 10 or 20 metres of that 
baby and it would be interesting :-)

Post a reply to this message

Darren New wrote:
> Bill Pragnell wrote:
>> although the basic premise for the gun is a real one, 
> 
> Sure. You try holding a weapon that fires something at relativistic speeds.

I meant the railgun aspect - accelerating the projectile using 
electromagnetics.

>> or the dubious claim that it can fire projectiles at near lightspeed 
> 
> That's what a railgun is for.

No it's not. A railgun accelerates a projectile with something like a 
linear accelerator. You get a fast-moving slug but I don't think 
anyone's under the illusion that it could be relativistic.

> You're only seeing the shockwave. ;-)

Hmm. *shakes head dubiously*

:)

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Darren New wrote:
> True. But to get the electrical propultion to work, the projectile needs 
> to be pretty small, which means it needs to go pretty fast. Otherwise 
> it's more of a thrower than a firearm. :-)

A railgun is exactly that - a thrower. A firearm uses chemical reactions 
to provide impulse.

You would never use one as a portable antipersonnel weapon anyway, it's 
probably more useful as a large scale space-based anti-ship or 
planet-busting weapon.

Post a reply to this message

Darren New wrote:
> (The railguns in the story actually had to fire 
> for a few thousand rounds to punch a hole in the atmosphere so the 
> needles wouldn't just vaporize.)

That's pretty cool. Relativistic weapons would only really be as useful 
as nukes - to cause almost-total destruction.

>> But anyway, even without relativity, the recoil would be absurd.
> Yep. If it can go thru a concrete wall coming out the front, the stock 
> can certainly break your shoulder.

It would do more than that. I can't be bothered with the sums right now 
but I imagine the recoil from a relativistic projectile gun would smash 
you to bits. You'd have to design any such gun to be recoilless somehow. 
<insert inertia-absorbing machinery here>

:)

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Bill Pragnell <bil### [at] hotmailcom> wrote:
> Darren New wrote:
> > Bill Pragnell wrote:
> >> although the basic premise for the gun is a real one, 
> > 
> > Sure. You try holding a weapon that fires something at relativistic speeds.

> I meant the railgun aspect - accelerating the projectile using 
> electromagnetics.

  Newton's third law still applies, even at relativistic accelerations.
If a force is applied to the projectile to make it accelerate at a certain
direction, another force will accelerate something else (ie. the gun)
at the opposite direction. I can't think of any way of avoiding that.

-- 
                                                          - Warp

Post a reply to this message

Warp wrote:
> Bill Pragnell <bil### [at] hotmailcom> wrote:
>> Darren New wrote:
>>> Bill Pragnell wrote:
>>>> although the basic premise for the gun is a real one, 
>>> Sure. You try holding a weapon that fires something at relativistic speeds.
> 
>> I meant the railgun aspect - accelerating the projectile using 
>> electromagnetics.
> 
>   Newton's third law still applies, even at relativistic accelerations.
> If a force is applied to the projectile to make it accelerate at a certain
> direction, another force will accelerate something else (ie. the gun)
> at the opposite direction. I can't think of any way of avoiding that.

Yes, I know all that. When I said 'basic premise' I was referring to the 
use of a magnetic field to accelerate the projectile, not the issues 
surrounding the claimed muzzle speed.

Hollywood gets projectile momentum transfer wrong all the time. Every 
time somebody gets shot by any kind of weapon, for a start.

Post a reply to this message

>  Newton's third law still applies, even at relativistic accelerations.
> If a force is applied to the projectile to make it accelerate at a certain
> direction, another force will accelerate something else (ie. the gun)
> at the opposite direction. I can't think of any way of avoiding that.

Bolt it to the Earth, then (assuming you're measuring recoil relative to the 
Earth) the recoil will be avoided.

Post a reply to this message

Bill Pragnell <bil### [at] hotmailcom> wrote:
> Hollywood gets projectile momentum transfer wrong all the time. Every 
> time somebody gets shot by any kind of weapon, for a start.

  Yes, it's funny how Hollywood physics are so skewed while still not
appearing completely wacky to the layman.

  For example, the faster the bullet, the farther it throws the person
who is hit by that bullet. In reality it's almost the opposite: The faster
the bullet, the less effect on the victim. The bullet just goes through
like a needle, and only little of its kinetic energy is trasnferred to
the victim itself. A slower bullet, however, transfers its kinetic energy
more to the victim because the body of the victim gets to slow down the
bullet, even so much that it might not even get through. In that case
the entire kinetic energy of the bullet is transferred. However, even in
that case the amount of kinetic energy is quite small compared to the
mass of an average person (the bullet is, after all, very light) and it
will not cause too much of an effect. Any minor effect will more likely
be overwhelmed by muscle spasms caused by the pain, which may cause the
victim to move to any random direction.

  (In some cases, if a fast bullet goes through, the jet effect caused
by the blood in the exit wound might even cause a movement towards the
shooter, not away from him... Still quite small, though.)

  Of course if we think about it in newtonian terms, if the victim gets
thrown back several meters, so should the shooter be too. The exact same
kinetic force is applied to the shooter, to the opposite direction.
(Well, technically speaking *more* kinetic energy is applied to the shooter
than to the victim because the bullet loses some kinetic energy during its
flight due to air friction, so if anything, the shooter should fly farther
back than the victim.)

  Then there are all those sparks. Bullets always send sparks when they
hit almost any surface. Of course real bullets don't, because bullets are
usually made of metals (such as copper) which do not spark even if they
hit some other metal. The movie makers themselves know this because they
can't get the sparks with real bullets but they must cheat (at least in
older and cheaper movies they used specially constructed "bullets" which
send sparks when they are broken).

  Those sparks have always bothered me. They make the scene unrealistic
and overboard. They don't add to the intensity of the scene.

  For a superb exception to this, see the beginning scene of Saving Private
Ryan. It's super-realistic. No bullet sparks. Yet the scene is extremely
immersive and intense. You can really *feel* the danger posed by those
bullets which you can't see but which are coming from everywhere.

-- 
                                                          - Warp

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Darren New wrote:
> Orchid XP v7 wrote:
>> range, and you can charge it up to deliver hits that can take down 
>> just about anything. (If you don't miss!)
> 
> You forgot "It shoots through walls", altho I must admit I never really 
> learned to take advantage of that feature, given the difficulty of 
> *aiming* thru walls.
> 

I remember that gun - excellent in DM games.

As others have said - one can get pretty good at where to shoot at the 
right times to get a kill.

I had some people pretty miffed at me sometimes because they couldn't 
hide anywhere...


Tom

Post a reply to this message

scott wrote:
>>  Newton's third law still applies, even at relativistic accelerations.
>> If a force is applied to the projectile to make it accelerate at a 
>> certain
>> direction, another force will accelerate something else (ie. the gun)
>> at the opposite direction. I can't think of any way of avoiding that.
> 
> Bolt it to the Earth, then (assuming you're measuring recoil relative to 
> the Earth) the recoil will be avoided.

That wouldn't half spoil the movie's storyline.

Post a reply to this message

Warp wrote:
> Bill Pragnell <bil### [at] hotmailcom> wrote:
>> Hollywood gets projectile momentum transfer wrong all the time. Every 
>> time somebody gets shot by any kind of weapon, for a start.
>   Yes, it's funny how Hollywood physics are so skewed while still not
> appearing completely wacky to the layman.

[snip detail]

Agreed - all of it. Maybe I read too much into realism, but I just can't 
take most action films seriously. The other things that are always wrong 
are explosions. A big pretty billowing fireball with hardly any force 
behind it is definitely not what a hand grenade does, or indeed any 
other explosive. A small firework and a gallon of fuel, maybe.

For a significant departure in this regard, watch The Kingdom. There's a 
car bomb explosion nearly halfway through that was done using real C4 
explosive, and it looks terrifyingly powerful. And very real.

That said, there are some very silly films that manage to mostly get 
this sort of thing right - True Lies, for example. Unlikely in the 
extreme, but most of the actual action isn't too far-fetched.

Post a reply to this message

scott wrote:
>>  Newton's third law still applies, even at relativistic accelerations.
>> If a force is applied to the projectile to make it accelerate at a 
>> certain
>> direction, another force will accelerate something else (ie. the gun)
>> at the opposite direction. I can't think of any way of avoiding that.
> 
> Bolt it to the Earth, then (assuming you're measuring recoil relative to 
> the Earth) the recoil will be avoided.

http://www.xkcd.com/162/

Post a reply to this message

Bill Pragnell wrote:

> Agreed - all of it. Maybe I read too much into realism, but I just can't 
> take most action films seriously.

Are you kidding?

There's 300 enemy troops with SMGs, grenades and rocket launchers, not 
to mention 3 helicopters, and yet 1 lone commando manages to shoot them 
all down without dying?

Need I explain further? ;-)

Post a reply to this message

On Thu, 25 Oct 2007 20:03:36 +0200, Orchid XP v7 <voi### [at] devnull> wrote:
> There's 300 enemy troops with SMGs, grenades and rocket launchers, not
  

> to mention 3 helicopters, and yet 1 lone commando manages to shoot the
m  

> all down without dying?

Not a problem, as long as there are enough RPG rounds conveniently lying
  

around.

http://www.wasabi.nu/filmklipp_visa.asp?id=771 (Flash required)


-- 

FE

Post a reply to this message

Bill Pragnell wrote:
> Darren New wrote:
>> (The railguns in the story actually had to fire for a few thousand
>> rounds to punch a hole in the atmosphere so the needles wouldn't just
>> vaporize.)
> 
> That's pretty cool. Relativistic weapons would only really be as useful
> as nukes - to cause almost-total destruction.
> 
>>> But anyway, even without relativity, the recoil would be absurd.
>> Yep. If it can go thru a concrete wall coming out the front, the stock
>> can certainly break your shoulder.
> 
> It would do more than that. I can't be bothered with the sums right now
> but I imagine the recoil from a relativistic projectile gun would smash
> you to bits. You'd have to design any such gun to be recoilless somehow.
> <insert inertia-absorbing machinery here>
> 
> :)

I think it would depend on the mass of the projectile, otherwise
headlights on cars would be pretty useless. Well, except maybe as
propulsion.

Post a reply to this message

Fredrik Eriksson wrote:
> On Thu, 25 Oct 2007 20:03:36 +0200, Orchid XP v7 <voi### [at] devnull> wrote:
>> There's 300 enemy troops with SMGs, grenades and rocket launchers, not 
>> to mention 3 helicopters, and yet 1 lone commando manages to shoot 
>> them all down without dying?
> 
> Not a problem, as long as there are enough RPG rounds conveniently lying 
> around.
> 
> http://www.wasabi.nu/filmklipp_visa.asp?id=771 (Flash required)
> 
> 

it wasn't a fair fight
he had a plunger!


Tom

Post a reply to this message

scott nous apporta ses lumieres en ce 2007/10/25 03:11:
>> Well, in an atmosphere, it would be like being hit by an explosion, as 
>> you pile up all the air in front of it.
> 
> Wouldn't something going that fast vaporize immediately when it hit the 
> air going that fast?  Doesn't stuff that going only a fraction of that 
> speed burn up in the outer atmosphere?
> 
>> Plus, don't forget all that nice gamma-burst radiation. (The railguns 
>> in the story actually had to fire for a few thousand rounds to punch a 
>> hole in the atmosphere so the needles wouldn't just vaporize.)
> 
> Ah yes, ok :-)
> 
>>> Well... technically a railgun (not to be confused with a coilgun) 
>>> fires projectiles using electrical propolsion. There's nothing in the 
>>> definition about how fast. ;-)
>>
>> True. But to get the electrical propultion to work, the projectile 
>> needs to be pretty small, which means it needs to go pretty fast. 
>> Otherwise it's more of a thrower than a firearm. :-)
> 
> In one of our lectures at university the dude had this rail-gun.  It was 
> about 2 metres long and plugged into the 420V 3-phase power supply.  He 
> loaded it with a brass (I think) solid lump of metal that was in a 
> pointy bullet shape.  It wasn't small, about 10cm diameter and 30cm 
> long.  When he flicked the switch it punched through (and got stuck in) 
> a big bit of wood just off the end of the bench he was using.  Rig up 10 
> or 20 metres of that baby and it would be interesting :-)
> 
> 
The bullet would have been hypersonic, not relativistic! Anyway, beter protect 
your ears when it fires... and don't stand anywhere close to that thing!

-- 
Alain
-------------------------------------------------
Lutheran: If shit happens, don't talk about it.

Post a reply to this message

Bill Pragnell nous apporta ses lumieres en ce 2007/10/25 06:28:
> Darren New wrote:
>> True. But to get the electrical propultion to work, the projectile 
>> needs to be pretty small, which means it needs to go pretty fast. 
>> Otherwise it's more of a thrower than a firearm. :-)
> 
> A railgun is exactly that - a thrower. A firearm uses chemical reactions 
> to provide impulse.
> 
> You would never use one as a portable antipersonnel weapon anyway, it's 
> probably more useful as a large scale space-based anti-ship or 
> planet-busting weapon.
Or as a satelite thrower.
Dig a large tunnel up some mountain near the equator, from about sea level to 
near the summit, line it up with proper circuitry. Load a specialy designed 
single stage rocket. Launch a 1000 tons payload into stationary orbit for less 
than $1 000 000.00! And you could do that every few hours.

-- 
Alain
-------------------------------------------------
You know you've been raytracing too long when you're starting to find these 
quotes more unsettling than funny.
     -- Alex McLeod a.k.a. Giant Robot Messiah

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scott wrote:
>> Well, in an atmosphere, it would be like being hit by an explosion, as 
>> you pile up all the air in front of it.
> 
> Wouldn't something going that fast vaporize immediately when it hit the 
> air going that fast? 

Yes. That's why it's like an explosion. :-)

> Doesn't stuff that going only a fraction of that 
> speed burn up in the outer atmosphere?

Pretty much.

>> Plus, don't forget all that nice gamma-burst radiation. (The railguns 
>> in the story actually had to fire for a few thousand rounds to punch a 
>> hole in the atmosphere so the needles wouldn't just vaporize.)
> 
> Ah yes, ok :-)

Of course, it was fun when they were sitting out on the airless moon, 
trying to shoot down the device orbiting the sun, or at least firing at 
the sun to see if they could get enough radiation to shut down the 
electronics on the thing orbiting the sun....

  --
   Darren New / San Diego, CA, USA (PST)
     Remember the good old days, when we
     used to complain about cryptography
     being export-restricted?

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Bill Pragnell wrote:
> Darren New wrote:
>> (The railguns in the story actually had to fire for a few thousand 
>> rounds to punch a hole in the atmosphere so the needles wouldn't just 
>> vaporize.)
> 
> That's pretty cool. Relativistic weapons would only really be as useful 
> as nukes - to cause almost-total destruction.

I've seen that too - drop stuff from orbit. These were basically 
anti-armor weapons. Attacking buildings and planes and satellites (from 
ground) and tanks and stuff like that. They felt bad when they got 
attacked indoors and had to shoot at the attacker with a bunch of 
unarmored enemy support troops about, because they all got smeared to 
red goo. :-)

Fun books.

> You'd have to design any such gun to be recoilless somehow. 

Generally by firing something out the back at a similar momentum. Kind 
of like the open back on a shoulder-launched rocket/bazooka thing.

-- 
   Darren New / San Diego, CA, USA (PST)
     Remember the good old days, when we
     used to complain about cryptography
     being export-restricted?

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Sabrina Kilian wrote:
>>> Yep. If it can go thru a concrete wall coming out the front, the stock
>>> can certainly break your shoulder.

> I think it would depend on the mass of the projectile, otherwise
> headlights on cars would be pretty useless.

Well, they don't go through concrete, do they? Certainly mine dont!


-- 
   Darren New / San Diego, CA, USA (PST)
     Remember the good old days, when we
     used to complain about cryptography
     being export-restricted?

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Bill Pragnell wrote:
>>> or the dubious claim that it can fire projectiles at near lightspeed 
>>
>> That's what a railgun is for.
> 
> No it's not. A railgun accelerates a projectile with something like a 
> linear accelerator. You get a fast-moving slug but I don't think 
> anyone's under the illusion that it could be relativistic.

I think it's more that it's the only technology that's likely to be able 
to accelerate something to relativistic speeds in a reasonable "barrel 
length."  Certainly an explosives-based lump-in-a-tube cannon won't.

-- 
   Darren New / San Diego, CA, USA (PST)
     Remember the good old days, when we
     used to complain about cryptography
     being export-restricted?

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Orchid XP v7 wrote:
> There's 300 enemy troops with SMGs, grenades and rocket launchers, not 
> to mention 3 helicopters, and yet 1 lone commando manages to shoot them 
> all down without dying?

That's what always un-immerses me in FPS games. In Quake II (IIRC) you 
wind up basically killing the entire enemy army yourself without ever 
seeing another living teammate.

-- 
   Darren New / San Diego, CA, USA (PST)
     Remember the good old days, when we
     used to complain about cryptography
     being export-restricted?

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>> Bolt it to the Earth, then (assuming you're measuring recoil relative to
>> the Earth) the recoil will be avoided.
>
> http://www.xkcd.com/162/

"Each turn robs the planet of angular momentum"

Unfortunately not...

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Darren New wrote:
> Bill Pragnell wrote:
>> You'd have to design any such gun to be recoilless somehow. 
> 
> Generally by firing something out the back at a similar momentum. Kind 
> of like the open back on a shoulder-launched rocket/bazooka thing.

That's the only method I've ever heard of, but I can't imagine it would 
work well for a hand-held relativistic projectile weapon! You'd end up 
standing at the cusp between two lobes of utter annihilation.

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Darren New wrote:
> Bill Pragnell wrote:
>>>> or the dubious claim that it can fire projectiles at near lightspeed 
>>>
>>> That's what a railgun is for.
>>
>> No it's not. A railgun accelerates a projectile with something like a 
>> linear accelerator. You get a fast-moving slug but I don't think 
>> anyone's under the illusion that it could be relativistic.
> 
> I think it's more that it's the only technology that's likely to be able 
> to accelerate something to relativistic speeds in a reasonable "barrel 
> length."  Certainly an explosives-based lump-in-a-tube cannon won't.

Maybe, but only if it's a very small projectile, and probably only 
useful in a vacuum (see your friction-vapourisation-explosion discussion 
above).

According to a quick shufti on google, a particle with a rest mass of 
1mg would need to be given 4.5 MJ of kinetic energy to get it to 0.01c, 
and about 450 MJ for 0.1c. I guess that's feasible as a weapon...

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scott <sco### [at] laptopcom> wrote:
> "Each turn robs the planet of angular momentum"

> Unfortunately not...

  I don't see, technically speaking, why not.

  Let's assume we have a big object in a weightless space in vacuum
rotating. Can this rotation be stopped by the object itself without
applying external forces?

  The answer is yes. The most obvious way to do this is to fire up some
rockets in specific directions. This causes the rotation to slow down,
basically by expelling material at high speed from the object.

  A slightly less obvious way is to rotate some significant part of the
object at a different speed. Why does this slow down the overall rotation?
It's because part of the angular momentum is converted into heat due to
friction, and this heat dissipation is taken away from this angular momentum.

-- 
                                                          - Warp

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>> "Each turn robs the planet of angular momentum"
>
>> Unfortunately not...
>
>  I don't see, technically speaking, why not.

Because you need angular *acceleration* to "rob the planet of momentum", not 
angular velocity.

Simply spinning at a constant 5000rpm is not going to change the planet's 
momentum, it will stay constant no matter how many times you turn or for how 
long you stay turning.

Of course spinning up to 5000rpm from 0rpm will change the momentum, but 
then spinning back down from 5000 to 0 will have precisely the opposite 
effect.

So, each turn, does not in fact, rob the planet of any momentum.

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scott <sco### [at] laptopcom> wrote:
> Because you need angular *acceleration* to "rob the planet of momentum", not 
> angular velocity.

> Simply spinning at a constant 5000rpm is not going to change the planet's 
> momentum, it will stay constant no matter how many times you turn or for how 
> long you stay turning.

  Take into account air friction and friction from the ground. In order to
maintain the constant turning speed you have to actually accelerate
constantly due to these frictions.

  Basically you can't have anything connected to the plane rotating at
a constant velocity without applying a force to it (because of friction).
And an applied force means acceleration.

-- 
                                                          - Warp

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>> Because you need angular *acceleration* to "rob the planet of momentum", 
>> not
>> angular velocity.
>
>> Simply spinning at a constant 5000rpm is not going to change the planet's
>> momentum, it will stay constant no matter how many times you turn or for 
>> how
>> long you stay turning.
>
>  Take into account air friction and friction from the ground. In order to
> maintain the constant turning speed you have to actually accelerate
> constantly due to these frictions.
>
>  Basically you can't have anything connected to the plane rotating at
> a constant velocity without applying a force to it (because of friction).
> And an applied force means acceleration.

Friction against what?  Newton's 3rd law...

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scott <sco### [at] laptopcom> wrote:
> Friction against what?  Newton's 3rd law...

  Against the ground and the air.

  Friction causes heat, and the energy for that heat must come from somewhere.
I cannot be produced from nothing.

  The answer is that the energy which produces that heat is coming from
the angular momentum, which is thus reduced by a proportional amount.

-- 
                                                          - Warp

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Darren New wrote:
> Orchid XP v7 wrote:
>> There's 300 enemy troops with SMGs, grenades and rocket launchers, not 
>> to mention 3 helicopters, and yet 1 lone commando manages to shoot 
>> them all down without dying?
> 
> That's what always un-immerses me in FPS games. In Quake II (IIRC) you 
> wind up basically killing the entire enemy army yourself without ever 
> seeing another living teammate.

An entire army is sent to the alien homeworld. The aliens wipe out all 
but 1 soldier, who is left armed with only a tiny pistol. Yet he alone 
is able to destroy an entire string of tactically significant targets, 
completely unaided.

Hmm. :-)

I guess the idea is to massage your ego by letting you be the 
super-soldier that nobody can kill.

Neat intro tho...

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