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Part of my magic system is the ability to shoot force at people. How much force (or at what speed) would cause an explosion on impact ?

Or, if that is impossible: let's say that matter is being pushed at an outrageous speed. How much speed would be needed to cause an explosion on impact ?

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    $\begingroup$ Are you talking about a chemical reaction, like dynamite exploding, or a sudden increase in air pressure, like the loud explosive noise of lightning? $\endgroup$ – Thom Blair III Dec 25 '16 at 2:49
  • $\begingroup$ @OP This isn't exactly an answer but at least warrants mentioning. Nuclear fusion is an extreme example of what you're going for. Smashing two atoms together with enough force will create a grand explosion. But to put it in perspective, the only time we've achieved that on earth is in a hydrogen bomb. Short of nuclear fusion, a bomb-like explosion from force alone probably isn't going to happen. What you can get however, is an explosion-like blast effect (think of throwing a rock into the water and creating a dramatic splash, only replace the water with your target and up the force). $\endgroup$ – thanby Dec 26 '16 at 17:14
  • $\begingroup$ If your definition of "explosion" extends beyond chemical reactions, then technically throwing a pebble into a pond creates an explosion of water. $\endgroup$ – Shufflepants Mar 29 '17 at 18:11
  • $\begingroup$ How much speed? Depends on how much mass you're throwing what it's made of, what it's hitting, and how big of an explosion you're after. $\endgroup$ – Shufflepants Mar 29 '17 at 18:12
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Explosions do not occur on impacts. That's a Hollywood myth that has no basis in reality. It exists because explosions sell movies.

An explosion occurs when a material spontaneously undergoes a rapid exothermic chemical reaction. For example, the most famously shock-sensitive explosive of them all, nitroglycerin, decomposes according to $4 \text{C}_3\text{H}_5\text{N}_3\text{O}_9 \rightarrow 12 \text{CO}_2 + 10 \text{H}_2\text{O} + 6 \text{N}_2+\text{O}_2$. It does so if the nitroglycerin molecule gets enough energy to undergo decomposition. In the case of nitroglycerin, that energy is low enough that kinetic force (such as being shaken) is enough to cause it to go off.

Most explosives are more stable than that. In fact, since the invention of nitoglycerin, the field of explosives devleopment has heavily focused on how to make explosives which are more stable. C4, for example, can be burned -- as in you can put it in a fire and it will burn rather than explode.

Your best bet is to simply declare that the explosions are a side effect of using the magic to "shoot force." Then you can decide at what point the explosions occur.

If you really want an explosion to occur, if you accelerate the material to just shy of the speed of light, you'll find that pretty much everything reacts with enough energy to call it an explosion. It still wouldn't be an explosion by the true definition of the word, but nobody would call the effect anything but extraordinary!

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    $\begingroup$ For some examples of the near-light-speed projectile, have a look at what-if.xkcd.com/1 $\endgroup$ – Matt Bowyer Dec 24 '16 at 20:49
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You can obtain an "explosion" by accelerating enough of the surface layer of an object to overcome the resistance of the object itself. The object doesn't so much "explode" as it is smashed.

In the case of a soft body made of 70%-plus water, a.k.a. human victim, the effect ought to be impressive enough.

Also, depending on your magic system, you might end up with "shovers" - able to exert a large amount of force but not to focus on a small enough surface, still effective against a vessel's sails, say -, "punchers" and "needlers" - these last, fully capable of killing someone by either accelerating a rib fragment through their heart, or stunning/killing them through hydrostatic shock.

Or...

If the traction is exerted at the molecular level, and at the correct "frequency", it can force open the bonds in the oxygen molecule and have them react with carbon in most organic matter. It is still not an explosion, but more a sort of flash fire - a "ripping" after which the target object's surface is subject to a very hot fire. For many substances (e.g. dry wood), this also means that the rest of the object will go up in flames in very short order.

For comparison, there's something like this in Vernor Vinge's first novel, The Witling. Natives of the planet Giri have the power of limited teleport, but energy is mostly conserved. So they can kill someone by mixing up their brains, teleport air or pebbles from the other side of the planet to make them into rotational-velocity shrapnel, or large rocks from far out moons to release kiloton-equivalent strikes.

Possibly, exerting force on a leaden bullet and launching it at someone might achieve something similar to a firearm. Which also gets interesting if the magicless population discovers the equalizing power of black powder :-)

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above ~70 km/s an impact causes any material being hit to vaporize (literally converted into a gas), this creates a secondary pressure wave thus creating an explosion just as detonating an explosive like TNT does. In thicker materials it creates an accompanying crater as the partially and completely molten material further away from the impact point is pushed out of the way by the pressure wave. There is quite a bit of wiggle room depending on the masses and materials in question. Some estimates say this can occur in rock at as little as 20km/s. At lower velocities the impact forces just creates a spray of molten material pushed away by the inertial forces creating a crater but not a real explosion.

https://www.rand.org/content/dam/rand/pubs/research_memoranda/2006/RM3490.pdf

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  • $\begingroup$ This is a great simple answer, but I think it could be improved if you explain what you mean by "vaporizing" and "creating an explosion" because they probably aren't the same effects the OP is thinking of. $\endgroup$ – thanby Dec 26 '16 at 17:07

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