Railguns, Plasma, Black Holes and all manner of nonsense.

Discussion in 'Discussions' started by OmniaNigrum, May 3, 2012.

  1. Haldurson

    Haldurson Member

    It would be so wrong of me for criticizing someone for going off on a tangent, simply because I'm guilty of that at times as well. I had a nickname given to me by my friends in High School -- I was "Mr. Non-Sequitor". I would explain that, except that I know that that would involve yet another derailment. :rolleyes:
    DavidB1111, Kazeto and OmniNegro like this.
  2. DavidB1111

    DavidB1111 Member

    One minor thing.
    It's amperage that kills people, not voltage.
    One hundred billion volts of electricity could flow through your body, but if it's at .00000001 miliamps, it's not going to kill you.
    It may mess you up, but it won't kill you.
    Electricity is weird. :)
    That said, I'd love to have an electrolaser.

    And I would imagine enough electricity on any machine is going to ruin it.
  3. OmniaNigrum

    OmniaNigrum Member

    The reason I used voltage is that since I did not mention amps in that particular sentence, we have to presume the amps remains the same. And the Wikipedia article about elecrolasers said the most common type used 10^9 or even as much as 10^10 volts. And obviously even with massive amperage, voltage is what makes it able to arc, so massive amperage is useless without massive voltage. (For the purpose of exploiting the plasma channel used by electrolasers.)

    A billion volts at 1 10^-20 amps would instantly stun you with almost zero physical damage. but a single volt at a few hundred or thousand amps would likely kill you.

    For the uninitiated, watts is the product of amps times volts. It can be any tow numbers and still relevant.

    My example would have made more sense using the word current, or specifying both sides of the equation.

    *Edit* I got my terms mixed up. According to Wikipedia, current means amperage.

    Here is a relevant quote:
    "Alternating current is sent through a series of step-up transformers, increasing the voltage and decreasing the current. The final voltage may be between 10^8 and 10^9 volts."

    *Edited Again* Since the post removed the power of numbers to make it appear it was saying 108-109 volts. That is supposed to be the tiny little 8 and 9 that I cannot put here since it is automatically nerfed into the full size number. Thus the ^s.

    For those who do not understand what that 10^8 means, take 10 and remove the zero. Now replace it with 8 of them. As 100,000,000. Thus 10^8 means one hundred million. 10^9 means a billion.

    Better idea. Read the link:
  4. DavidB1111

    DavidB1111 Member

    I actually knew that.
    I think I may have miscommunicated a bit.
    Also, the human body needs something small like 7 miliamps to kill you.
    That's 7/1000s of an amp.
    Also, it's stunning ability is also relegated by it's amperage. At that low of an amperage, one billion volts isn't going to do anything but make you go, "Oh my!" like you're trying to imitate George Takai. :)
    Essence likes this.
  5. OmniaNigrum

    OmniaNigrum Member

    Lol. I did not account for the Ohms required to pass skin, but besides that, what I said makes sense. Seven milliampes is the actual number? That I did not know. I always figured it was a small amount, but that makes my statement incorrect. 10^-20 amps is 0.00000000000000000001 amps. :) :) :)
  6. mining

    mining Member

    There's a lot of wrong in this thread.

    E=MC^2 has nothing to do with why a railgun will kill you. The two equations you'd be after are p=mv and E=1/2mv^2.

    F=dp/dt, i.e. rate of change of momentum. If you want to kill someone, you want it to have a lot of momentum and either a) Keep the momentum (i.e. shooting through things/putting holes in people) or b) stop dead. b) is typically the frame of design behind bludgeoning medieval weapons, a) is the frame of design for modern guns.

    Worth mentioning:
    This is blatant crap. Sorry to say that, but if you can make a metallic substance no longer transfer current, go for a nobel prize right at this instant.
    Yes, they will degrade, melt, whatever, but thats because you have something moving really, really, really fast that generates a lot of heat, and a large opposite force from Newton's Third Law.

    Also, as discussed the ridiculo-huge fireball is because the air behind it will combust.

    Plasma, as discussed, is cool and all, but its nothing special. Its just ions and a cloud of electrons.

    This one's interesting. Its not that they don't let them exist, its just that most objects of that scale will have masses and masses of interactions with the air particles around them - indeed, proportionally more than most other things, because volume increases as the cube, and area increases as the square of radius. Because of this, they get a lot of heat, and melt. Really fast. If you were to shoot off, say, an alpha particle at 10^7 ms^-1 - of the same order of magnitude as their speed in alpha decay - it slows down quickly. It probably only travels a few metres, but regardless - it can go really, really fast.

    Hrmm. The only other real thing re: nuclear weaponry is that the basic theory is really, really obvious. Get some stuff that'll fuse (hydrogen in a H-bomb) or fission (U,Pu, etc.) in a traditional nuke, and find some way to reach a critical mass. The science and physics isn't all that hard, but its very, very involved - you need to account for literally everything, or you can have an absolute disaster.

    Umm, there's a lot here, but re: voltage and current:

    Ohm's law states that V=IR, hence for constant resistance Voltage is directly proportional to current. Its really, really hard to have a billion volts at 1*10^-20 amps.

    Watts are better defined as joules per second, i.e.
    Also, magnetars are fairly reasonable - black holes for example are generally considered to be confirmed to exist, and *must* have density greater than that mentioned.
    Kazeto likes this.
  7. OmniaNigrum

    OmniaNigrum Member

    As mentioned in the IRC chat, we are both partly wrong. I was wrong to say it would not remain conductive. I was right to say it would increase resistance to the point that it would be nearly unconductive. I think that this in and of itself makes my statement quoted above true, but read for yourselves.

    Evidence is on Wikipedia. Here is a quote: (For those who prefer to skim only the essentials of these walls of text, look at the bold parts most.)

    A railgun consists of two parallel metal rails (hence the name) connected to an electrical power supply. When a conductive projectile is inserted between the rails (at the end connected to the power supply), it completes the circuit. Electrons flow from the negative terminal of the power supply up the negative rail, across the projectile, and down the positive rail, back to the power supply.[6]
    This current makes the railgun behave as an electromagnet, creating a powerful magnetic field in the region of the rails up to the position of the projectile. In accordance with the right-hand rule, the magnetic field circulates around each conductor. Since the current is in the opposite direction along each rail, the net magnetic field between the rails (B) is directed vertically. In combination with the current (I) across the projectile, this produces a Lorentz force which accelerates the projectile along the rails. There are also forces acting on the rails attempting to push them apart, but since the rails are mounted firmly, they cannot move. The projectile slides up the rails away from the power supply.
    A very large power supply, providing on the order of one million amperes of current, will create a tremendous force on the projectile, accelerating it to a speed of many kilometres per second (km/s). 20 km/s has been achieved with small projectiles explosively injected into the railgun. Although these speeds are possible, the heat generated from the propulsion of the object is enough to erode the rails rapidly. Under high-use conditions, current railguns would require frequent replacement of the rails, or to use a heat resistant material that would be conductive enough to produce the same effect.


    The power supply must be able to deliver large currents, sustained and controlled over a useful amount of time. The most important gauge of power supply effectiveness is the energy it can deliver. As of December 2010, the greatest known energy used to propel a projectile from a railgun was 33 megajoules.[7] The most common forms of power supplies used in railguns are capacitors and compulsators which are slowly charged from other continuous energy sources.
    The rails need to withstand enormous repulsive forces during shooting, and these forces will tend to push them apart and away from the projectile. As rail/projectile clearances increase, arcing develops, which causes rapid vaporization and extensive damage to the rail surfaces and the insulator surfaces. This limited some early research railguns to one shot per service interval.
    The inductance and resistance of the rails and power supply limit the efficiency of a railgun design. Currently different rail shapes and railgun configurations are being tested, most notably by the United States Navy, the Institute for Advanced Technology, and BAE Systems.

    Materials used

    The rails and projectiles must be built from strong conductive materials; the rails need to survive the violence of an accelerating projectile, and heating due to the large currents and friction involved. The recoil force exerted on the rails is equal and opposite to the force propelling the projectile. The seat of the recoil force is still debated. The traditional equations predict that the recoil force acts on the breech of the railgun. Another school of thought invokes Ampère's force law and asserts that it acts along the length of the rails (which is their strongest axis).[8] The rails also repel themselves via a sideways force caused by the rails being pushed by the magnetic field, just as the projectile is. The rails need to survive this without bending and must be very securely mounted.

    Heat dissipation

    Massive amounts of heat are created by the electricity flowing through the rails, as well as by the friction of the projectile leaving the device. The heat created by this friction itself can cause thermal expansion of the rails and projectile, further increasing the frictional heat. This causes three main problems: melting of equipment, decreased safety of personnel, and detection by enemy forces. As briefly discussed above, the stresses involved in firing this sort of device require an extremely heat-resistant material. Otherwise the rails, barrel, and all equipment attached would melt or be irreparably damaged.
    In practice the rails are, with most designs of railgun, subject to erosion due to each launch; and projectiles can be subject to some degree of ablation also, and this can limit railgun life, in some cases severely.
    Kazeto likes this.
  8. mining

    mining Member

    Note that resistance caused by great heat can be mitigated in theory.
  9. DavidB1111

    DavidB1111 Member

    Ah. THank you for explaining it, Mining.
    I don't mind being wrong.

    I thought that E=MC2 makes sense for this, because you're throwing a decent mass object at a decent speed.

    After all, there are the relativistic kill weapons which would basically launch a massive tungsten rod at the ground at over 25% of the speed of light, hitting the ground with so much force, and energy, that it acts like a nuclear detonation without the radiation side effects.
    They're called Rods from Gods. :) And that's just one use of high speed weapons.
    I guess my knowledge on how energy is transferred is a little off. My bad. I'm not a physicist, you might be, but I'm not.
    I'm just a nerd.
  10. Kazeto

    Kazeto Member

    When human-made kinetic weapons become capable of launching the projectiles at the speed of light (I don't think that will ever happen, since we'll kill ourselves before that), we can use E=MC^2 for calculations. Otherwise, we just use the generic calculations for kinetic energy (just like mining pointed out higher in the thread).

    @OmniNegro: So, to sum it up, currently railguns are just like the long-range bombardment cannons (like "Schwerer Gustav", for example), in that they can be used, but shooting too frequently will cause the rails to get destroyed after less shots, and there is a limit of shots after which the rails have to be changed to fresh ones.
  11. OmniaNigrum

    OmniaNigrum Member

    The idea of a railgun is just a series of strong electromagnets. They are damaged by every last shot the fire. And each time, the resistance ramps up, requiring more to actually make the next shot possible.

    The rails being electromagnets do take damage every shot. But the fact that every shot must be fired with as much possible power as can be provided to be any better than conventional weapons makes them take even more damage. By far at that. The wires providing power would partly melt every shot, some parts of the electromagnets would become magnetized even when power was removed, and a whole slew of other problems would come up too.

    In short, for a potent railgun, it requires changing out or at least inspecting and replacing certain parts every last time it is fired.

    If you read about the railguns that have been used, you will notice that the articles carefully separate the potency of the shot from the number of shots it could potentially fire in a given time. There is good reason for this. More power = more damage, both to the target struck by the railgun, and to the railgun itself.

    As I said before the best possible very fast moving energy weapon is not a railgun, but an electrolaser. Defenses can be built for this, but with a potent enough capacitor bank and a strong enough chemical laser, you can bypass just about anything.

    To clarify, the laser, (Probably an Oxygen-Iodine laser) heats the air until it becomes partly plasmatic. At that point it is conductive. The hotter the laser makes the air, the more conductive. And thus when you arc current through the laser, it can and will ride the path of least resistance.

    If you were to point the chemical laser at a target several kilometers away that is surrounded by lightning rods, you would need a greatly more potent laser to maintain a path of least resistance between the lightning rods or the current would arc to the nearest of those when fired.

    A potent chemical laser is currently quite possible with our technology. And it could be repeatedly fired without requiring much maintenance. Railguns cannot say the same.

    In fact, conventional chemical propelled weapons like artillery are far better than railguns unless you absolutely must hit as fast as possible. In such a case the question of how many times must you be able to fire before you have to rebuild the whole damned thing is the defining factor between weather a railgun or a electrolaser is best.

    Note that a disposable airborn chemical laser could be fired from altitude to make a temporary path of least resistance through clouds for an almost certain lightning strike at the place on the ground being targeted.
  12. DavidB1111

    DavidB1111 Member

    Thanks, Kazeto for explaining it.
    My bad.

    Also, while Railguns are still far away from being uber-practical, at least they're not going to fall victim to bullet drop. :) They'll be affected by gravity, don't get me wrong, but the faster the object, the less gravity affects it.
    Gravity is after all, the weakest force in the universe.
    If it was as strong as any of the others, you would weight as much as a galaxy. :eek: Or close to it.
  13. Aegho

    Aegho Member

    Relativity has an effect, which is likely more than negligable but still minor in relation to the effect of simple kinetic energy.

    An example of how relativity has an effect at far lesser speeds is GPS. GPS is affected by both special and general relativity, and that is accounted for and corrected by the code in the satellites. If this correction did not take place, then in one day, GPS would become off by 11 miles. This is known because one of the engineers on the original experimental GPS project didn't believe in relativity, so they were programmed with a switch that turned the corrections on and off. (I know this because I'm a Neil DeGrasse Tyson fan, and watched the 2012 Isaac Asimov Memorial Debate, it's on youtube).

    Incidentally the 3rd edition of swedish pen&paper roleplaying game Mutant had plasma weapon where the authors must've had a pretty decent grasp of what plasma is. It was named the Gehenna Puker, and was basically a flamethrower on steroids. You had to wear a protective suit to fire it safely, or heat proximity would cook you.

    Oh and a weapon that fires pre-made plasma would operate on similar principles as a railgun. Plasma is affected by electromagnetism. The sun occasionally fires extremely hot, huge streams of plasma towards the earth, but this is nothing to be alarmed about because it gets drawn towards the earth's magnetic poles and dissipates harmlessly against our atmosphere. This is what causes the northern lights, aurora borealis.
  14. Haldurson

    Haldurson Member

    As long as we are talking about futuristic weaponry, I should mention one of my favorites from SF. Larry Niven 'invented' something he named a 'Variable Sword' (this predates the Light Saber from Star Wars by quite a bit). It's an extendable monofilament wire held in place by an alternating stasis field, and could cut through almost anything. Here's a link to a description: http://news.larryniven.net/concordance/main.asp?alpha=V

    Obviously, this is so out there that it could be considered fantasy at this point. But it is probably one of my favorite science fictional weapon. It's probably not coincidental that a few of my favorites were also from Niven's Known Space series. Most notable, I think, was a Tnuctip spy weapon found in a Slaver stasis box in the short story "The Soft Weapon". The really cool thing about it was that it could transform itself into many different types of weapons. http://news.larryniven.net/concordance/main.asp?alpha=T#Tnuctipspyweapon
  15. Aegho

    Aegho Member

    My favorite SF weapon is one that while being for personal defense is not actively used by the defended party. Sentient drones the size of marbles, with forcefields, and really powerful propulsion(and a few other tricks). Think of it as a living bullet that can hover, change direction on a dime, and think for itself. From Ian M Bank's culture series, possibly "Use of Weapons" or "Inversions", but I'm not sure. Can turn a room full of people into swiss cheese at the blink of an eye.

    One of the more novel SF weaponry though, that's really in a league of its own in the wtf factor, is from the game Warhammer 40k. An Orc weapon named Shock Attack Gun. It opens a small warp portal and then sends snotlings(tiny little orclings) through the warp, unprotected, where they're scared insane by the demons that occupy the warp, the other warp gate is at the weapon's target... results vary from being attacked by snotlings driven mad with fear outside any armor worn... or attacked from inside the armor... or *splat* they end up inside the target, with messy results.
  16. mining

    mining Member

    Well, its less that, but more it needs to spend less time moving so it doesn't have as much time to accelerate downwards. Its sure as hell still accelerating at 9.81m/s^2 towards the ground. The formula for displacement given constant acceleration (IM A PHYSICIST SO I IGNORE AIR RESISTANCE AND FRICTION) is s=ut+0.5at^2. For a really short time interval, displacement in the vertical direction is gonna be really small with a shitty acceleration of 9.8 :). So yeah, I'm agreeing with you but clarifying: g is constant for all objects, its just that for small times and high velocities the effects are less apparent.

    This is kind of right, kind of wrong. Gravity is really, really strong over really large masses.

    Both gravity and electromagnetism follow a similar rule:

    F=G*m*M/r^2 <== Gravity

    F=k*Q*q/r^2. <== EM

    Here's the thing - k=9.11*10^9.

    k is 10^20 times larger than G.

    BUT, a charge in coulombs that we are likely to encounter is only of the order of http://en.wikipedia.org/wiki/Orders_of_magnitude_(charge)

    A thundercloud has charge on the order of 10^1 coulombs.That's a lot.

    In contrast, http://en.wikipedia.org/wiki/Orders_of_magnitude_(mass)

    The sun and earth have masses on the order of 10^30 and 10^24 respectively. And they're puny compared to the 10^40 kg of some black holes.

    Charges are rarely found isolated - you will rarely have a magnitude of 1 coulomb of one charge.

    In small examples where mass and charge are both really small - say electrons and protons - charge certainly dominates. But over quantities that exist in real life? Gravity certainly prevails, despite the fact that it has such a small proportionality constant.
    Essence likes this.
  17. DavidB1111

    DavidB1111 Member

    Oh. Neat! Thanks for explaining it easily to me.
  18. Aegho

    Aegho Member

    Another interesting fact of black holes: One reason they're called singularities is that conventional physics doesn't work normally inside their event horizon(the general theory of relativity states that the matter of a black hole is compressed into an infinitely dense point). I can't find a good internet link to it but one explanation I've read goes as follows: due to the vast mass of a black hole, its gravity well bends space time very sharply around it, so that where its actual matter is, space acts as if there is more than three dimensions, or possibly even is more than three dimensions(I seem to recall something about its mass/volume ratio, ie: density being explainable by using 6 dimensional space).

    Incidentally a black hole with a mass less than 1.4 times that of the earths sun becomes a neutron star.
  19. mining

    mining Member


    A black hole with a low mass is just a smaller black hole - a black hole is defined by its mass/volume -
    An object whose radius is smaller than its Schwarzschild radius is called a black hole. The surface at the Schwarzschild radius acts as an event horizon in a non-rotating body (a rotating black hole operates slightly differently). Neither light nor particles can escape through this surface from the region inside, hence the name "black hole". The Schwarzschild radius of the (currently hypothesized) supermassive black hole at our Galactic Center would be approximately 13.3 million kilometres.


    Also - of course conventional physics doesn't work inside their event horizon - 'conventional' physics doesn't even work on a lot of stuff we can do on earth, i.e. GPS, atom smashing, so on so forth.
  20. OmniaNigrum

    OmniaNigrum Member

    David, a rather dumbed down version of what mining said in math way above my head regarding gravity is this:

    Gravity is the most potent force ever. A single particle in a galaxy on the other side of the observable universe can be measured *HERE* if you had a detector strong enough. It has zero boundaries. No other force can have the same said of it.