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[Splint]

Yeah, but dwarven technology defies all logic. That crossbow may have fired copper, but who's to say if the munitions guy didn't core it with lead or something?

And besides, in DF, looking for logic we can understand is like trying to find a tooth on the floor of a bar mid bar fight. It won't happen too easily.

[Corai]

Dwarf fortress logic = tomatoes


Logic = Logic


Thats my explanation for dwarf fortress and what it does. Enjoy your flying kobolds.

[Escapism]

You've got some... points. Did some calculations and assuming I'm not misinterpreting the wikis numbers, a bronze bolt would weigh 1.2 kg. Neat. Or a stack of bronze bolts, idk. The latter makes more sense, as that would mean a bronze bolt in-game weighs ~50 gram.

[Splint]

I like my homemade railguns better. A poorly aimed shot will shatter bones,. Centermass will be fatal as they get smacked with enough force to splatter them into chunky mustard ona wall, tree, or what have you.

[GenJeFT]

Actually, from some quick research, a crossbow could send a kobolt flying a little bit.

A kobold is smaller then a dog, so I am going to compare it with a European wolf which weigh around 38.5 kilograms. Which is not that much.

Kobolds would weigh less then that, how much less I don't really know, so I am going to guess they weigh around 22.7 Kilograms, or around the size of an 8 year old child.

I cant find any units for the force of a crossbow in metric so I am going to convert the weight to English.

A child weighs around 50 to 60 pounds. A cross bow bolt has the force of about 86.78 ft-lbs. So I think a cross bow would readily knock over a kobolt without much trouble. Depending on the bolt of course.

[Urist Da Vinci]

Link to my research thread on "propelled by the blow" back from before the minecart update, when objects didn't travel in parabolas. Things work somewhat differently now, and I don't intend to redo the research at this time.

http://www.bay12forums.com/smf/index.php?topic=107575.0

My hunch is that the velocity of bolts is static, and when you use a denser material for the bolts it increases the momentum, which causes small creatures like kobolds to get knocked back.

As far as I could test, the momentum of the bolts is static, and so is the damage and knockback, but changing the mass of the bolt only means that it goes a bit faster or slower. If it tries to go too fast, it's velocity will be capped to the MAXVEL of the crossbow.

[dennislp3]

one thing the combat report doesn't state is how far it skid across the ground. The system only recognized that it did. For all we know it moved an inch. I think people see skid and have grand ideas of something flying across the floor.

[Splint]

I see skid and usually interpret it as them slamming into the ground, not sliding across it. Unless they actually do slide some distance.

[Shmo]

 We can always approach this quantitatively, keeping in mind the oddness of units. I will not assume 1Γ = 1kg (this proves immaterial and someone cleverer than I would eliminate mass by defining specific inertia). Explicitly SI measures like body volume will, however, be treated as such. Should I make an error in my appraisal of units or scales - which is likely given I'm generally unfamiliar with raws - feel free to correct me. We proceed:

Taking the density of the kobold to be that of water = ρ_w Γ/L, we have the mass of an adult kobold to be 20ρ_w Γ. [2]

Now, looking at SHOOT_FORCE, if this is indeed a force and not impulse, doesn't tell us about the resultant momentum of the bolt. Thus we consider the bolt to travel at MAX_VEL = 1000 [3], the units of which are dubious. cm/s gives 36km/h exit velocity. Real crossbows can have an exit velocity closer to 350 km/h [1], so we assume good dwarven crossbows actually fire the bolt at 1000 dm/s = 100m/s.

The size of a bolt is listed as 150 [3], assumed reasonably to be cm^3. The density of copper is given to be 8930 [3], which we infer to be 8.39ρ_w Γ/L from the real life density of copper. From this we get the mass of one bolt is 0.150*8.390ρ_w Γ ~ 1.26ρ_w Γ.

From this we get the momentum of the launched bolt is 125.85ρ_w Γm/s. By conservation of linear momentum this must equal the momentum of the final kobold-bolt system, whose velocity we shall denote by v. Then: v*21.26ρ_w Γ = 125.85ρ_w Γm/s => v ~ 5.92m/s = 21.3km/h.

Not too shabby, I dare say. The skidding is physically justified under the MAX_VEL assumption. The root cause seems to be the unnaturally high exit velocity of the crossbow, which would in more realistic circumstances be, probably, half of what it is.

It is left as an exercise for the reader to visualize what would happen to a kobold baby (HINT: mass = 1ρ_w Γ [2]).

---
References:

[1] http://en.wikipedia.org/wiki/Projectile
[2] http://dwarffortresswiki.org/index.php/Kobold
[3] vanilla Arch Linux 0.34.11 raws

---

P.S. We have ignored the vector nature of velocity - the kobold-bold system will naturally proceed in the direction of the bolt. Assuming this is at least roughly horizontal, skidding indeed seems like a physically legitimate outcome.

P.P.S. If it weren't so late I'd do an analysis of how far the kobold should travel given some uncontroversial assumptions about coefficients of friction (though deriving g_Γ from circumstances might be non-trivial). I might yet return to this problem, this is terribly fun.

[Sus]

Congratulations Shmo, you earn a ☼forgotten beast silk sock☼ for some A-grade dwarven ‼Science‼.