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Fantasy world, very reliant on magic and magical creatures, but as close as possible to the standard rules of physics (it's science-based magic).

I want to create a bow that shoots lightning-embedded arrows, but I want it to be stealthy. Is there any way to make lightning quiet enough to not be noticed by anyone ? (Light is not an issue in this case, only sound is.)

The lightning follows the momentum of the arrow (which is made of a magical metal); it won't ground completely until it hits a target, but it will lose the lightning if it passes near something made of conductive metal.

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    $\begingroup$ Just to be clear, does the arrow BECOME a lightning bolt when fired or fire as a normal arrow and THEN hit someone with lightning? $\endgroup$ – Friendlysociopath May 13 '17 at 7:48
  • $\begingroup$ Unless you are shooting just under your own feet, it will hardly be like real lightning. Please give us some details, for Example how do you want it not to ground immediately, if you want this to be answerable $\endgroup$ – Mołot May 13 '17 at 7:50
  • $\begingroup$ @Friendlysociopath the bow shoots normal arrows, surrounded by a lightning that enhances its speed (basically an arrow inside a lightning) $\endgroup$ – JackIta May 13 '17 at 7:57
  • $\begingroup$ You should not use the tags 'science-based' and 'magic' together. If you want to use magic, even rules based magic, then our world's science does not apply. So please remove the 'science-based' and 'physics' tags, or else it is unclear what you are asking. $\endgroup$ – kingledion May 13 '17 at 11:52
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    $\begingroup$ @kingledion It's not hard-science - only science-based. $\endgroup$ – wizzwizz4 May 13 '17 at 14:45
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In this question I am not sure where the lightning is coming from. I will assume there is some source of charge at or near the archer.

From OP: "the lightning follows the arrow". But the lighting will be lost if the arrow goes too near a conductive surface.

An arrow that dragged a wire could then complete a circuit when it hit a large creature, and that would be quiet. That is basically a taser. Normal sparks ionize a path in the air. I suppose the arrow could do this. I think a path of ionized plasma would not persist for the time of an arrow flight but there is magic to stabilize it.

As I understand thunder it happens because there is resistance in the air to the movement of the current. The resistance heats the air rapidly and the expansion of the air makes the noise.

The lower the resistance the less heat. Less heat = less expansion. Less expansion = less noise.

So: if you have your arrow shed superconducting magic particles in a path behind it, your electricity would flow silently down that path to ground in your large creature.

If the arrow was too close to a conductive structure the arc would be from your magic superconducting path through the air. That would be regular air plasma with resistance and it might crackle or otherwise make noise.

If the lightning arrow really imparts a lot of energy, resistance issues in the target might make noise. Lightning can make things full of water explode because resistance in the wet thing turns water into steam, and expanding steam can blow things up. You see this most often with trees. I have heard this once and it is loud.

enter image description here
from http://www.cbc.ca/news/canada/manitoba/tree-lightning-strike-explode-winnipeg-1.3640417

If something similar happens to your large target that would not be very stealthy. The target itself probably would not notice.

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Thunder comes from the air being super-heated by the lighting, expanding -- thus leaving a low-pressure area -- and the cooling air collapsing back in on itself with... a bang.

To make silent, magic lightning, say either (a) that it's cold lightning (because "magic"), or (b) that there's a force field around the lightning which hold the air in. When the force field disintegrates, you would have thunder, though, and that would increase damage done.

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    $\begingroup$ @JackIta the problem is that "Fantasy world, very reliant on magic and magic creatures" breaks physics. So, just say that it's "cold lightning". $\endgroup$ – RonJohn May 13 '17 at 8:29
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    $\begingroup$ Can you have lightning in a vacuum? $\endgroup$ – ggdx May 13 '17 at 10:50
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    $\begingroup$ instead of a forcefield that holds air in you could have one that holds it out; create a vacuum where the lightning will pass. without air there's no thunder. $\endgroup$ – Annonymus May 13 '17 at 11:15
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    $\begingroup$ @JackIta how "close as possible to the standard rules of physics" is close enough? $\endgroup$ – RonJohn May 13 '17 at 14:52
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    $\begingroup$ @DanWhite Not really, no. Lightning requires the movement of charge and something needs to carry that charge. If you just shoot electrons through a vacuum that's not lightning, it's just directed beta radiation. In fact, the main reason lightning glows the way it does is because of the fact that it's created an extremely hot plasma. Without that it would probably be mostly invisible. $\endgroup$ – Kyle May 13 '17 at 15:36
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The lightning arrow is the magical equivent of a taser. Until it makes contact and is earthed, there is no discharge until then. As it discharges through the target body, there is little or no noise. The arrow itself, I see as a magical capacitor, activated when it leaves the bow, discharging on contact. As an apprentice, the game was to charge up a capacitor and throw it to someone. When they instinctivly caught it...zap!

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  • $\begingroup$ tasers works differently, they create a circuit with your body. $\endgroup$ – JackIta May 13 '17 at 8:25
  • $\begingroup$ Analogy is always a bit suspect :-) $\endgroup$ – Wayne Watson May 13 '17 at 8:27
  • $\begingroup$ What is a "lightning arrow"? Is it real or fictitious? $\endgroup$ – Hot Licks May 13 '17 at 11:37
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    $\begingroup$ Lightning also creates a circuit with your body. Tasers use a wire and lightning or any spark ionizes a conductive plasma path in the air. Then the current flows down the wire or plasma path. $\endgroup$ – Willk May 13 '17 at 12:52
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Thunder actually is caused by the super-heated air around the electron stream, can be as loud as 120 dB close by and will be heard for miles around.

However there are also odd forms of lightning like ball lightning, which is not really defined by science (yet).

So if you go with 'low energy' bolts you should be able to achieve silence, but for one thing: Electricity will not 'spark' through the air at low energy.

So I would recommend going for a visual effect lightning-like effect or find a 'magic' way to make air conductive.

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  • $\begingroup$ the problem is that a low energy bolt not be enough, for story reason i need something that can cause very much troubler to very big creatures, that means a lot of energy $\endgroup$ – JackIta May 13 '17 at 8:39
  • $\begingroup$ @JackIta precision can make up for lack of energy. Zap the brain, monster will fall down. $\endgroup$ – Bookeater May 13 '17 at 11:08
  • $\begingroup$ @JackIta is it acceptable if the arrow carries a low voltage in flight and then discharges a larger blast when it hits? Sort of like a magic taser only more damaging in the end? This would logically create a thunderclap when the arrow strikes its target, but it would be silent in flight. $\endgroup$ – Steve-O May 13 '17 at 16:17
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The sound of thunder comes from the violent expansion of super heated air around the bolt. If the air around the channel slowly heated up then the sound would be much less. So have the lightning bolt build on a ramp. That is to say turn up its voltage slowly, don't have it discharge all at once.

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You could have the magic metal that makes up the arrow as some kind of super-conductive metal that also absorbs static electricity from the air. This would mean that, ideally after firing it, it would gather electricity from the air, and on impact, discharge it.

You could complete some kind of circuit upon firing, to allow the electricity to start building; so you're not carrying around an ever increasing amount of electricity that would very much like to ground through, well, you.

I don't know if it would still cause a thunder-like reaction when the electricity discharges into whatever solid object the arrow hits (instead of just into the air). Then again, that might be exactly what you're looking for.

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  • $\begingroup$ By what mechanism would a charged object pick up like charge from the air? $\endgroup$ – kingledion May 13 '17 at 21:14
  • $\begingroup$ @kingledion That's where I'm leaning on the whole magical metal part, as far as I know, this kind of effect would be impossible without it. $\endgroup$ – Azrantha May 16 '17 at 10:57
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The answer may lie in your magic metal and not the lightning. You could spell it to absorb sound in the vicinity, which would negate the thunder and also the cry of the victims when shot.

If you wanted to go scientific, it would absorb the heat from the lightning.

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  • $\begingroup$ "it would absorb the heat from the lightning" which would then be discharged in the target (which would not be stealthy). $\endgroup$ – RonJohn May 13 '17 at 16:27

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