I love the questions I ask for research

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I need some kind of yardstick by which to gauge the destructive potential of one stick of dynamite. Presuming it was jammed into a device built largely of sturdy wood nailed together, how large of a device could the dynamite effectively destroy? (For values of “destroy” that equal “render it completely inoperable, such that the thing can’t really be repaired.”)

I know that’s a very imprecise description, and I’ll be getting imprecise answers, but it would be nice to know if one stick would be enough to trash, say, a car-sized target, or more, or less.

0 Responses to “I love the questions I ask for research”

  1. marydell

    Look up “stick of dynamite” on youtube and you’ll see a lot of examples of half sticks & whole sticks being used to blow stuff up…mostly small-to medium stuff. Unfortunately a lot of the videos don’t do a good job of showing after effects, so in the one where they blow up a fridge with a stick of dynamite, it’s not clear how blowed up it really done got.

    Based on these videos, I’d think you could blow a big hole in a car engine with one stick dynamite, but to blow the whole car up you’d probably need one of those bundles of six or eight sticks together that they always have in cartoons.

    Wikipedia has a big article on dynamite and another on relative destructive capabilities of explosives, but I don’t speak Math so couldn’t really see an answer there. Mythbusters blows stuff up all the time, so their site may help.

    • Marie Brennan

      It isn’t actually a car I’m trying to blow up; that was just a unit of size. I’ll check Youtube, though — good suggestion!

  2. drydem

    the real trick to demolitions is placement and containment. If you blow up an m80 on an open palm, you have a bad burn. If you blow up an m80 in a closed fist, you no longer have a hand.
    assuming the stick of dynamite could be placed in a reasonably enclosed location, it could cause all manner of mischief. Just throwing it at something would probably cause only cosmetic damage.

    • alecaustin

      Yeah, object density is and the containment of the explosion is highly relevant here. Wikipedia claims that a stick of dynamite contains 2.1 MegaJoules of energy, but how thoroughly contained the explosion is determines how much of that energy actually yields destruction.

      Should be pretty easy to do some back-of-the-napkin math to determine how much energy is being transferred per square inch at a given distance from the explosion, assuming a spherical stick of dynamite. (Not a reasonable assumption, of course. But you probably don’t need mathematical precision here either, and if you need a better approximation, adding the surface area of a cylinder to that wouldn’t be too hard.)

      Really, the important bit in terms of tearing apart a wooden structure would probably be which of the bits closest to the explosion survive to have energy transferred to them and then fly off to transfer that energy to other things, preferably breaking themselves and those other things in the process. A MegaJoule is about the amount of kinetic energy that a speeding one-ton car, and speeding cars do a very good job of rendering themselves largely irreparable if they wrap themselves around something, so my instinct is that having a single stick of dynamite destroy a car-sized wooden object could be credible if A) the explosion happened near the center of the object, B) was sufficiently contained or channeled to increase the effective yield of the explosion, and C) if the wooden object wasn’t that sturdy to begin with. If you’re talking a car-sized structure made of thick planks and heavy logs, though, one stick isn’t going to be enough.

      (Also, explosions don’t set things on fire unless they spread around flammable substances as well as sparks, given that the explosion’s shockwave snuffs out flames. But you probably knew that already.)

  3. Anonymous

    Well, there are several factors involved (putting on my hat as having commanded an aircraft maintenance squadron that included both EOD and bomb-dump components):
    * How much fluid (air) space is inside that “sturdily built” object. The more hollow space there is, the more opportunities there are for rapidly heated and pressurized air to do its destructive work; and, similarly, the smaller the holes allowing outside access for that air there are, the more fun the air will have finding a way out.
    * Proper treatment of the dynamite. Dynamite is not a solid; it is a liquid suspension of (largely) nitroglycerin in sawdust. Each stick has to be physically rotated a partial turn every so often; the military uses a sixty-day rotation schedule with really, really dire consequences for screwing up either the task or the recordkeeping. Dynamite that hasn’t been treated properly won’t explode with a predictable effect… and, too often, can explode at the wrong time entirely.
    * The quality and nature of the joinery. Are we talking about nailed together (but nonethless sturdy, like a house)? Glue-and-screw (and what kind of glue)? Fully dovetailed/mortise-and-tenoned? For sudden stresses, the joints of a wooden construct are usually the weak points.
    * What kind of wood was used? There’s a huge difference in strength between a structure built of kiln-dried white oak and the same structure, built with the same techniques, out of hastily adzed square green fir.

    I know that just adds more questions instead of answering the initial one. Welcome to the world of making things go boom, which is as much an art as a science.

    • Marie Brennan

      I figured you’d have input on this. 🙂 My answers to your points are on the vague side — the thing being blown up isn’t too precisely described — but I’ll keep those factors in mind.

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