POV-Ray : Newsgroups : povray.off-topic : I miss this Server Time
12 Oct 2024 07:14:28 EDT (-0400)
  I miss this (Message 38 to 47 of 137)  
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From: Darren New
Subject: Re: I miss this
Date: 26 Oct 2007 00:56:49
Message: <47217391$1@news.povray.org>
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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From: Darren New
Subject: Re: I miss this
Date: 26 Oct 2007 00:57:45
Message: <472173c9$1@news.povray.org>
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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From: Darren New
Subject: Re: I miss this
Date: 26 Oct 2007 01:00:36
Message: <47217474$1@news.povray.org>
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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From: Darren New
Subject: Re: I miss this
Date: 26 Oct 2007 01:01:24
Message: <472174a4$1@news.povray.org>
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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From: scott
Subject: Re: I miss this
Date: 26 Oct 2007 03:21:45
Message: <47219589$1@news.povray.org>
>> 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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From: Bill Pragnell
Subject: Re: I miss this
Date: 26 Oct 2007 05:36:44
Message: <4721b52c@news.povray.org>
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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From: Bill Pragnell
Subject: Re: I miss this
Date: 26 Oct 2007 05:59:00
Message: <4721ba64$1@news.povray.org>
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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From: Warp
Subject: Re: I miss this
Date: 26 Oct 2007 06:34:24
Message: <4721c2af@news.povray.org>
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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From: scott
Subject: Re: I miss this
Date: 26 Oct 2007 08:18:16
Message: <4721db08$1@news.povray.org>
>> "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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From: Warp
Subject: Re: I miss this
Date: 26 Oct 2007 08:32:32
Message: <4721de5c@news.povray.org>
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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