tinman Posted November 3, 2005 Author Report Share Posted November 3, 2005 Re: A question to the physics-minded... Sounds like it's mainly something that would be used on one's self, though. Or maybe the user (who obviously didn't buy Personal Immunity) was in the 'area of effect' when he set it off... Quote Link to comment Share on other sites More sharing options...
prestidigitator Posted November 3, 2005 Report Share Posted November 3, 2005 Re: A question to the physics-minded... Aren't there already-working prototypes based on just this principle? Yeah. I'm still a bit skeptical, but it is certainly within the realm of possibility. Feasibility and practicality are another question, but when has Sci-Fi been put off by that? Quote Link to comment Share on other sites More sharing options...
pinecone Posted November 3, 2005 Report Share Posted November 3, 2005 Re: A question to the physics-minded... If you don't mind getting a little freaky(and comic book physics Is pretty freaky...) Take a look at "Super cavitating projectiles" they do exist, but are for underwater use...add in a little "razzle dazzle" and you've got your low friction hyper velocity projectiles.... Quote Link to comment Share on other sites More sharing options...
Jaxom Posted November 3, 2005 Report Share Posted November 3, 2005 Re: A question to the physics-minded... Yes, they do...but they all fall at the same rate. If the projectile is traveling fast enough, it may reach its target well before it's fallen a significant distance. ... Edit: and if anyone wants, I'll be happy to run the numbers and prove that. It's not like it's a difficult set of equations or anything. Ok, so... Let's run through the numbers (since I used to do this for a living)... Assume no air-friction (which is, actually, exactly what the original goal was) and hence the projectile travels at muzzle velocity for the duration of its flight and gets to ignore wind. Muzzle velocities for common projectiles today vary from 1200-3000 ft/s (google "muzzle velocity", speed of sound in air at sea level on earth is 1100 ft/s roughly). That means that a projectile will take anywhere from 1.6 to 4.5 seconds to travel 1 mile. Now, another nice thing about gravity is that you get to do vector math. Doesn't matter whether the object suffering gravity is flying sideways at hypersonic velocity or not. You can do this test at home, kiddies. Drop a ball and see how far it travels in 1.6 seconds. Again, ignoring air friction and using earth gravity of 32 ft/s^2 (9.8 m/s^2) the distance an object falls in 1 second is 16 ft (d = 1/2 g t^2). And I say again... This is why you don't see hunters using laser sights. Even a target at 100 yards being shot with a high-powered hunting rifle (using the Winchester site and comparing high-grain 30-06 and 338 loads you get muzzle velocities of under 2800 ft/s, http://www.winchester.com/products/catalog/rifle.aspx) so at 100 yards you're looking at over 1/10th of a second flight time and a drop of roughly (1/2 * 32 * 12 * 1/10 * 1/10) or just under 2 inches. Laser sights look cool in the films and all but you're now looking at a laser with a diameter or 2 inches to shoot something 50 game-scale inches away. (Can you tell I used to teach this stuff and know the real-world examples?) By the time you get to ionizing a large enough area for a projectile to travel a mile you should have just made that laser into a focussed beam and burned a hole through your target anyway. Even if you assume super-science and create a mock load that could get you a muzzle velocity of 10,000 ft/s (3 times more power than we can manage safely today) you still get a travel time of 1/2 second for a mile and that means a drop of 4 feet. Quote Link to comment Share on other sites More sharing options...
Cancer Posted November 3, 2005 Report Share Posted November 3, 2005 Re: A question to the physics-minded... Jaxom and I mentioned those (supercavitating projectiles) over lunch today, oddly enough. The supercavitating projectiles aren't supersonic, though that's partly because of the huge difference between the speeds of sound in water and air. (The speed of sound in air is really piddly slow.) Also, those projectiles are rockets: it takes a pretty impressive amount of power, continuously applied, to keep those going. My impression from the papers discussing ABM system alternatives is that trying to shoot down stuff coming from space from a groundbased platform is very difficult. Missiles work better than directed-energy weapons, for several reasons, not least of which are the huge power requirements for the energy weapons. Most people agree that orbital platforms are likely to be much more effective. They are also prohibited by treaty, though, so development of such systems has been arrested. Quote Link to comment Share on other sites More sharing options...
Dr. Anomaly Posted November 3, 2005 Report Share Posted November 3, 2005 Re: A question to the physics-minded... Even if you assume super-science and create a mock load that could get you a muzzle velocity of 10' date='000 ft/s (3 times more power than we can manage safely today) you still get a travel time of 1/2 second for a mile and that means a drop of 4 feet.[/quote'] You know, you're absolutely right about that. I was making some incautious assumptions in my head rather than working through the actual numbers. Nice catch. Quote Link to comment Share on other sites More sharing options...
Jaxom Posted November 3, 2005 Report Share Posted November 3, 2005 Re: A question to the physics-minded... If you don't mind getting a little freaky(and comic book physics Is pretty freaky...) Take a look at "Super cavitating projectiles" they do exist' date=' but are for underwater use...add in a little "razzle dazzle" and you've got your low friction hyper velocity projectiles....[/quote'] http://en.wikipedia.org/wiki/Supercavitation Super cavitation is a mute point in air. It only applies in liquids. The closest comparison in a gaseous medium is a bow-shock and bullets are already super-sonic so again, moot point. Quote Link to comment Share on other sites More sharing options...
prestidigitator Posted November 3, 2005 Report Share Posted November 3, 2005 Re: A question to the physics-minded... Even if you assume super-science and create a mock load that could get you a muzzle velocity of 10' date='000 ft/s (3 times more power than we can manage safely today)....[/quote'] Well, since (at non-relativistic speeds) energy is proportional to the square of the velocity, the 10,000 ft/s muzzle velocity requires more like ten times the energy than the 3,000 ft/s muzzle velocity you mentioned being the high end of today's projectiles. And that's neglecting the fact that incidental losses probably aren't going to go up linearly. But that's nitpicking. Quote Link to comment Share on other sites More sharing options...
Jaxom Posted November 3, 2005 Report Share Posted November 3, 2005 Re: A question to the physics-minded... Now, don't get me wrong here... I'm happy to go with projectiles at Mach 30 (33,000 ft/s) and assume instantaneous flight times and straight paths. Once you assume materials stronger than what we have on earth today, you get to do that. I'm all for Adamantium or Mithril gun barrels. Once you have those you can upgrade the powder charge in the projectiles. We've got characters with super-running breaking the speed of sound in spandex. You're certainly allowed to play with the physics as much as you want but to get a projectile to follow a stright line for any "long-range shot" of a mile you're going to be looking for speeds upwards of Mach 70 (which gets you a flight-time of less than 1/14 of a second and a drop of less than an inch). Modern material strengths can withstand an explosion yielding almost Mach 3. Quote Link to comment Share on other sites More sharing options...
Jaxom Posted November 3, 2005 Report Share Posted November 3, 2005 Re: A question to the physics-minded... Well' date=' since (at non-relativistic speeds) energy is proportional to the square of the velocity, the 10,000 ft/s muzzle velocity requires more like ten times the energy than the 3,000 ft/s muzzle velocity you mentioned being the high end of today's projectiles. And that's neglecting the fact that incidental losses probably aren't going to go up linearly. But that's nitpicking. [/quote'] Ok, ok... So I misused the word power. Picky, Picky. (Who was it with the sig that went, "Hello, Mr. Kettle? This is Mr. Pot. You're black." ?) Quote Link to comment Share on other sites More sharing options...
prestidigitator Posted November 3, 2005 Report Share Posted November 3, 2005 Re: A question to the physics-minded... Ok, ok... So I misused the word power. Picky, Picky. (Who was it with the sig that went, "Hello, Mr. Kettle? This is Mr. Pot. You're black." ?) Well, you are abusing your power. That is always worth addressing. Quote Link to comment Share on other sites More sharing options...
prestidigitator Posted November 3, 2005 Report Share Posted November 3, 2005 Re: A question to the physics-minded... Oh hell! Let's just apply a little UBO Teleportation that Must Cross Intervening Space to the projectiles and be done with it. No need to worry about air resistance! (My classmate was seriously going to work on quantum-mechanical teleportation research for his graduate physics work. I never did find out where that went--I'm a little skeptical, as usual. I'll have to e-mail him some day.) Quote Link to comment Share on other sites More sharing options...
Jaxom Posted November 4, 2005 Report Share Posted November 4, 2005 Re: A question to the physics-minded... What exactly is your definition of quantum mechanical teleportation? I seem to remember an explicit proof in quantum that an electron didn't have to travel through the intervening space to move from any one point in the probability distribution to any other. Seems to me that, if I recall, this had something to do with the fact that the s-orbital meant that the electron actually overlapped the proton but that's been far too many years. Funny, as a matter of fact, that this should come up since it is exactly the argument that I am using for a "power-armor" character that I am working on right now to take teleportation. By day she's a Nobel Laureat Quamtum Field specialist. By night she runs around in a spandex suit. (So what are the odds of every particle in your body tunnelling at exactly the same instant? Put it this way, straight-line projectiles are a *much* better physical approximation. ) Quote Link to comment Share on other sites More sharing options...
ghost-angel Posted November 4, 2005 Report Share Posted November 4, 2005 Re: A question to the physics-minded... So .... what's the recoil like one on of these suckers? Quote Link to comment Share on other sites More sharing options...
prestidigitator Posted November 4, 2005 Report Share Posted November 4, 2005 Re: A question to the physics-minded... What exactly is your definition of quantum mechanical teleportation? Increasing to near unity the probability that all particles of a macroscopic object will, "instantaneously," move to a far away location in their original configuration. IOW, think Star Trek teleporters, essentially; just without the scrambling, buffering, and reassembling parts. (So what are the odds of every particle in your body tunnelling at exactly the same instant? Put it this way, straight-line projectiles are a *much* better physical approximation. ) All going in the same direction, moving a significant distance, and winding up in the same configuration from which they started? Let's just say not very likely. Not very likely at all. That's if quantum mechanics even has it right and this is truly possible. I'm not entirely convinced that quantum mechanics has quite the correct model; it's just the best we have at the moment, and it does seem to work reasonably well. Quote Link to comment Share on other sites More sharing options...
austenandrews Posted November 4, 2005 Report Share Posted November 4, 2005 Re: A question to the physics-minded... I'm not entirely convinced that quantum mechanics has quite the correct model; it's just the best we have at the moment' date=' and it does seem to work reasonably well. [/quote'] I think that's pretty much the universal sentiment about QM. Quote Link to comment Share on other sites More sharing options...
tinman Posted November 4, 2005 Author Report Share Posted November 4, 2005 Re: A question to the physics-minded... Ok, so... Let's run through the numbers (since I used to do this for a living)... Assume no air-friction (which is, actually, exactly what the original goal was) and hence the projectile travels at muzzle velocity for the duration of its flight and gets to ignore wind. Muzzle velocities for common projectiles today vary from 1200-3000 ft/s (google "muzzle velocity", speed of sound in air at sea level on earth is 1100 ft/s roughly). That means that a projectile will take anywhere from 1.6 to 4.5 seconds to travel 1 mile. Now, another nice thing about gravity is that you get to do vector math. Doesn't matter whether the object suffering gravity is flying sideways at hypersonic velocity or not. You can do this test at home, kiddies. Drop a ball and see how far it travels in 1.6 seconds. Again, ignoring air friction and using earth gravity of 32 ft/s^2 (9.8 m/s^2) the distance an object falls in 1 second is 16 ft (d = 1/2 g t^2). And I say again... This is why you don't see hunters using laser sights. Even a target at 100 yards being shot with a high-powered hunting rifle (using the Winchester site and comparing high-grain 30-06 and 338 loads you get muzzle velocities of under 2800 ft/s, http://www.winchester.com/products/catalog/rifle.aspx) so at 100 yards you're looking at over 1/10th of a second flight time and a drop of roughly (1/2 * 32 * 12 * 1/10 * 1/10) or just under 2 inches. Laser sights look cool in the films and all but you're now looking at a laser with a diameter or 2 inches to shoot something 50 game-scale inches away. (Can you tell I used to teach this stuff and know the real-world examples?) By the time you get to ionizing a large enough area for a projectile to travel a mile you should have just made that laser into a focussed beam and burned a hole through your target anyway. Even if you assume super-science and create a mock load that could get you a muzzle velocity of 10,000 ft/s (3 times more power than we can manage safely today) you still get a travel time of 1/2 second for a mile and that means a drop of 4 feet. Just to nit-pick... The reason we don't generally see the Hollywood-style lasersight on long range firearms (i.e. the one that projects a dot on the target as opposed to the one that projects a dot in the middle of an optical sight) is because you can't reliably see a projected laser dot at 300 meters, and because the bright light would tip off your target (be it a deer or whatever). If you bore-sight a scope on a rifle your cross-hairs will indicate an impact point several inches too high at several hundred yards. If you bore-sight a projection laser sight you will get the same result. In either device all you are doing is indicating an impact point, so if a projected laser dot was a practical optical guide at such a distance all one would have to do is adjust it to account for the ballistic path just as one does a normal scope. But it's not, so the point is kind of moot Quote Link to comment Share on other sites More sharing options...
tinman Posted November 4, 2005 Author Report Share Posted November 4, 2005 Re: A question to the physics-minded... Now, don't get me wrong here... I'm happy to go with projectiles at Mach 30 (33,000 ft/s) and assume instantaneous flight times and straight paths. Once you assume materials stronger than what we have on earth today, you get to do that. I'm all for Adamantium or Mithril gun barrels. Once you have those you can upgrade the powder charge in the projectiles. We've got characters with super-running breaking the speed of sound in spandex. You're certainly allowed to play with the physics as much as you want but to get a projectile to follow a stright line for any "long-range shot" of a mile you're going to be looking for speeds upwards of Mach 70 (which gets you a flight-time of less than 1/14 of a second and a drop of less than an inch). Modern material strengths can withstand an explosion yielding almost Mach 3. What if you were to use magnetic acceleration, rather than pressure from expanding gases? Assuming for a moment that the initial acceleration and the projectile flight path could be in vacuum, wouldn't the practical upper limit on velocity be divorced from the ability of the gun barrel material being able to withstand pressure? Quote Link to comment Share on other sites More sharing options...
tinman Posted November 4, 2005 Author Report Share Posted November 4, 2005 Re: A question to the physics-minded... So .... what's the recoil like one on of these suckers? If it were an action movie, the only certanty would be that the target would experience an impact an order of magnitude greater than the recoil of the weapon, propelling him backwards through a plate-glass window that would (if necessary) have been transported behind him a fraction of a second earlier through quantum teleportation. Quote Link to comment Share on other sites More sharing options...
Sean Waters Posted November 4, 2005 Report Share Posted November 4, 2005 Re: A question to the physics-minded... You could just build it and say that is how it works....mind you that probably misses the point, doesn't it? Could you abandon projectiles and use a low powered laser to ionise the air then use the ionised chanel to whack a huge charge into the target from a long way away: lightning bolts have a hell of a range, the problem has always been aiming them....I am not suggesting this from a hard science POV but it sounds reasonable.... Quote Link to comment Share on other sites More sharing options...
tinman Posted November 4, 2005 Author Report Share Posted November 4, 2005 Re: A question to the physics-minded... You could just build it and say that is how it works....mind you that probably misses the point, doesn't it? Could you abandon projectiles and use a low powered laser to ionise the air then use the ionised chanel to whack a huge charge into the target from a long way away: lightning bolts have a hell of a range, the problem has always been aiming them....I am not suggesting this from a hard science POV but it sounds reasonable.... Yeah, that's another good option. So far it seems the following all work as reasonable extrapolations of our current understanding and technology: -very high energy lasers (the classics never get old), -ultra-high speed projectiles that use a plasma tip to create a channel for themselves through the atmosphere, and -laser-ionised tunnel-guided electrical discharge projectors. I think this is the beginning of some bad times for the PC's Quote Link to comment Share on other sites More sharing options...
tinman Posted November 4, 2005 Author Report Share Posted November 4, 2005 Re: A question to the physics-minded... Thanks to everyone for your input so far, you've given me a lot to work with Quote Link to comment Share on other sites More sharing options...
prestidigitator Posted November 4, 2005 Report Share Posted November 4, 2005 Re: A question to the physics-minded... What if you were to use magnetic acceleration' date=' rather than pressure from expanding gases? Assuming for a moment that the initial acceleration and the projectile flight path could be in vacuum, wouldn't the practical upper limit on velocity be divorced from the ability of the gun barrel material being able to withstand pressure?[/quote'] If you could truly guide the projectile accurately using an electromagnetic field, and could operate in a vacuum, doubtless you could lose a lot less energy in the process (for example, generating no sound in an explosion and eliminating friction between the projectile and the gun barrel) and thus be a lot more energy-efficient. Also, the only things you would have to worry about material-wise are ensuring that the material of the projectile allows for your method of accelleration (probably means being ferromagnetic) and that it does not shear apart due to internal stresses caused by the forces used to accelerate it (not likely, but if you are dealing with really high field strengths/accelerations it could start to become an issue). However, this doesn't allow you to escape the fact that it takes energy to accelerate a projectile, and the net aim of a weapon is to deliver that energy in some fashion to the target. So you will always be limited by the size of energy supply you carry and the rate of power delivery. What we need are cold micro-fusion generators. Oh, and room-temerature superconductors so the coils don't have to be the size of a house. Quote Link to comment Share on other sites More sharing options...
prestidigitator Posted November 4, 2005 Report Share Posted November 4, 2005 Re: A question to the physics-minded... If it were an action movie' date=' the only certanty would be that the target would experience an impact an order of magnitude greater than the recoil of the weapon, propelling him backwards through a plate-glass window that would (if necessary) have been transported behind him a fraction of a second earlier through quantum teleportation.[/quote'] So true! Rep. Quote Link to comment Share on other sites More sharing options...
tinman Posted November 4, 2005 Author Report Share Posted November 4, 2005 Re: A question to the physics-minded... If you could truly guide the projectile accurately using an electromagnetic field' date=' and could operate in a vacuum, doubtless you could lose a lot less energy in the process (for example, generating no sound in an explosion and eliminating friction between the projectile and the gun barrel) and thus be a lot more energy-efficient. Also, the only things you would have to worry about material-wise are ensuring that the material of the projectile allows for your method of accelleration (probably means being ferromagnetic) and that it does not shear apart due to internal stresses caused by the forces used to accelerate it (not likely, but if you are dealing with [i']really[/i] high field strengths/accelerations it could start to become an issue). However, this doesn't allow you to escape the fact that it takes energy to accelerate a projectile, and the net aim of a weapon is to deliver that energy in some fashion to the target. So you will always be limited by the size of energy supply you carry and the rate of power delivery. What we need are cold micro-fusion generators. Oh, and room-temerature superconductors so the coils don't have to be the size of a house. Hmmm. Maybe I'll stick to more conventional options. Thanks for the insight Quote Link to comment Share on other sites More sharing options...
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