Falling into water?

[Drakevarg]

Simple question that's been bugging me:

If a character falls into the water, the DMG states that if the water is at least 10 feet deep then the first 20 feet of the fall don't count, the next 20 feet count as nonlethal damage, and all distance after that is lethal.

What they DON'T bring up is the question of "when do you stop falling?" Do you stop at the surface? 10 ft. down, since that's the requirement for a buffered fall? At the bottom?

The last one seems unreasonable, since what if you fall into the ocean? Or worse, the Plane of Water? The second one might work, but it isn't actually mentioned. The surface seems unlikely because it's just too abrupt.

What do you think?

[Yora]

If it ever should be important, I'd say 10 feet in.

[Bhaakon]

That really depends on the player's swim skill and how much crap he's carrying, no?

Olympic swimmer in his skivvies? 10 ft sounds right.
Barbarian in full plate with backpack full of gold bars? He's not stopping until bedrock.

[Trixie]

What do you think?

*Breaks out my Physics Testbook* How detailed answer do you want? :smallamused:

[Knaight]

*Breaks out my Physics Testbook* How detailed answer do you want? :smallamused:

Seems like a good method to me. Crank details up all the way, and lets see what you get. :smallwink:

[excruciarch]

It's all about how you enter the water after the fall and what you do after the submersion. And the total weight you carry on your legs. Taking player's Swim and Load into account while calculating the *point of stoppage* seems pretty reasonable to me.

[Trixie]

Seems like a good method to me. Crank details up all the way, and lets see what you get. :smallwink:

Well... I'm too busy now to give proper evaluation, seeing very important thing to calculate when considering air/fluid resistance would be drag ratio (mostly, shape of the object), but my guess would be, it would be ranging between 20:1 (20 feet of fall to 1 feet underwater) in case of light, dragging objects (wooden shield hitting water side-wise), 10:1 (halfling landing on his belly), 5:1 (normal object), 2.5:1 (laden adventurer landing legs/head first) or even 1:1 (sword hitting water tip-first), or course, afterwards the object would continue to sink unless effort to stop this would be made.

Note that this doesn't exactly work for truly high speeds - if you hit water too fast (generally, faster than it can move out of the way), it becomes rigid as steel, and energy the normally would be used to break surface and sink will be used to make big splash and disintegration of the object in question, unless it's pretty hard and drag low (the sword from above) but even in this case it will be damaged.

[excruciarch]

2 Trixie
Even considering all that surface tension thing water can't get as rigid as steel. Even frozen water can't. A sword made of tempered steel won't be damaged even after falling from considerable height with the maximum speed G-force can grant. =)

[Trixie]

Even considering all that surface tension thing water can't get as rigid as steel. Even frozen water can't. A sword made of tempered steel won't be damaged even after falling from considerable height with the maximum speed G-force can grant. =)

Really? Care to explain why anti-tank bullets made from substances considerably harder than steel fragment, ricochet or break up when fired into water? Do you have an idea how much energy you need to pump into fluids to make them move once you exceed certain barriers (such as sound of speed in a given fluid) when displaced by object hitting the water to get the fluid to move?

Surface tension has nothing to do with it, fluid physics do.

[excruciarch]

Best AMR bullets are made of depleted uranium. It is more likely to break than get deformed, like lead bullets do. And the usual 50*99 NATO cartridge contains so much powder, that it brings the barrel energy to the point of accelerating 50 to 100 gram slug way beyond the speed of sound. =) That's not something you can accomplish by throwing a sword down from a helicopter, right?
(even then yo can't compare water to steel judging only by the bullet destruction)

[Knaight]

Note that this doesn't exactly work for truly high speeds - if you hit water too fast (generally, faster than it can move out of the way), it becomes rigid as steel, and energy the normally would be used to break surface and sink will be used to make big splash and disintegration of the object in question, unless it's pretty hard and drag low (the sword from above) but even in this case it will be damaged.

Tests done regarding human terminal velocity at pretty much any breathable atmospheric pressure indicate that it is below the speeds needed for this. Excruciarch mentioned swords, and while I'm not familiar with the terminal velocity of falling swords in various pressures, I suspect they are somewhere below those of a bullet.

[kardar233]

Yeah. You hit water at terminal velocity, you're going to break a whole bucket of bones and maybe pulp some internal organs.

Your sword's gonna be fine though.

[Trixie]

Best AMR bullets are made of depleted uranium. It is more likely to break than get deformed, like lead bullets do.

They break because (surprise!) DU bullets are made from baked-together[1] uranium powder, making them rather non-malleable, precisely to spread as much of the stuff around when they penetrate armor. And, actually, they're not the best, sadly.

[1] Translated term from my notes, precise English equivalent might be slightly different but I don't have time to look for it.


And the usual 50*99 NATO cartridge contains so much powder, that it brings the barrel energy to the point of accelerating 50 to 100gram slug way beyond the speed of sound. =) That's not something you can accomplish by throwing a sword down from a helicopter, right?

"Barrel energy"? Pardon? :smallconfused:

You meant 'exit velocity', perhaps? Energy =/= velocity =/= acceleration.

Actual speed of 12.7x99mm NATO bullet in the air or amount of power has nothing to do with with speed of sound in the fluid, which is rather different than in-air one, and I noted speed of sound in the fluid in just many of such barriers. Try to imagine difference between punching loose sand and punching said sand fused solid into 30 mm thick glass plate, and you won't even come close.

And actually, if the sword is dropped from high enough, and it has good drag/weight ratio, it could conceivably reach much higher speed than any bullet simply due to square/cube law.

Plus, 12.7 mm bullet weights around ~40 grams, some heavy types reaching ~50 grams, certainly not '100gram' (order of magnitude more).


(even then yo can't compare water to steel judging only by the bullet destruction)

Um... yes, I can. I took university-grade physics course, and material technology courses during my IT education. It was a few years ago, but I bet I still know more about that than any random D&D player, no offense.

[excruciarch]

Yeah. You hit water at terminal velocity, you're going to break a whole bucket of bones and maybe pulp some internal organs.

Your sword's gonna be fine though.

Terminal velocity for concrete or even solid steel (if you're lucky enough to find something big enough made of steel to fall on ) is nowhere near that of the water's.
10m fall on some concrete- you are done for, 10m fall on some water- you are alive and your kidneys are still intact. Hooray.
And a sword falling down on some concrete with final speed possible for a free fall is in trouble...

[Trixie]

Tests done regarding human terminal velocity at pretty much any breathable atmospheric pressure indicate that it is below the speeds needed for this. Excruciarch mentioned swords, and while I'm not familiar with the terminal velocity of falling swords in various pressures, I suspect they are somewhere below those of a bullet.

Human terminal velocity. We are notably not made from steel.

One example of objects dropped from above would be a tool bag (http://blogs.orlandosentinel.com/news_space_thewritestuff/2008/11/so-why-does-a-n.html) that actually burned in the atmosphere from friction, having attained speed of a few km/s prior to that, higher than any kind of bullet ever made, despite rather non-aerodynamic shape.

Yes, I don't postulate dropping the sword from the ISS, but breaching speed of sound is certainly possible, given the right shape/mass. You can't compare swords to bullets simply to huge difference of surface/mass advantage sword has due to cube/square law.


Terminal velocity for concrete or even solid steel (if you're lucky enough to find something big enough made of steel to fall on ) is nowhere near that of the water's.
10m fall on some concrete- you are done for, 10m fall on some water- you are alive and your kidneys are still intact. Hooray.
And a sword falling down on some concrete with final speed possible for a free fall is in trouble...

So, you say human body can reach speed of sound falling from 10 meters? How? :smallconfused:

And what has the object's composition to do with its terminal velocity? :smallconfused:

As for finding something made out of steel to fall on, there are so many things you'd need to be lucky to not have one nearby, though I don't know what it has to do with falling on water.

[excruciarch]

And, actually, they're not the best, sadly.
They are. Ones with steel core are not. But they are cheap and effective.

And this entire conversation is more like about how much energy an object will lose on point of entry. That defines the whole overload thing and the initial damage an object will take. Just shoot some nine caliber into water, concrete and steel, goddammit =)))
Since I've studied physics in a Russian high school my terminology can seem off. =)
PS
Like it or not, but at any speed the impulse on point of entry will differ for all substances.

[Knaight]

Human terminal velocity. We are notably not made from steel.


Sword terminal velocity in systems with meaningful atmospheric pressure is obviously much higher than human, that much is obvious. Of course, if a sword is falling from the sky in a fantasy setting -which is what is being looked at here- odds are good its attached to somebody.

[Drakevarg]

Fascinating as the physics stuff is, you have to keep in mind that DnD is a world where gravity isn't 9.8 m/s^2, but 150 ft. for the first 6 seconds and 300 ft. every 6 seconds after that. Also, the party rogue is a catgirl and calculating terminal velocity and whatnot around her would probably be fatal.

Anywho, the general gist is that it would be pretty much completely ad hoc then, yeah?

[Rogue Shadows]

Fascinating as the physics stuff is, you have to keep in mind that DnD is a world where gravity isn't 9.8 m/s^2, but 150 ft. for the first 6 seconds and 300 ft. every 6 seconds after that.

That's really just for flying creatures...I go with the somewhat dirty, but also more accurate, 500 ft on the first round and 1000 feet each round thereafter.


Anywho, the general gist is that it would be pretty much completely ad hoc then, yeah?

Probably. As a quick-and-dirty rule I'd say you sink 10 feet for every 30 feet you fell, up to a maximum of sinking 50 feet. Until I'm given a better quick-and-dirty, that is.

[King Atticus]

Just have a hungry Dragon Turtle down there, then how deep the entry or how much damage from the fall becomes a moot point. :smallbiggrin:

[Drakevarg]

Just have a hungry Dragon Turtle down there, then how deep the entry or how much damage from the fall becomes a moot point. :smallbiggrin:

There's already Chuuls swimming around down there to encourage them to find a dry spot, pronto. The party is a 6-man 3rd level party, so a Chuul is theoretically survivable. Not that I would encourage them to fight it out.

[HalfDragonCube]

There's already Chuuls swimming around down there to encourage them to find a dry spot, pronto. The party is a 6-man 3rd level party, so a Chuul is theoretically survivable. Not that I would encourage them to fight it out.

*Insert witty Chuul/O-Chuul pun here*

Too tired for funniness...

[Kalaska'Agathas]

Stormwrack has more detailed rules for falling into water, I believe. It doesn't give a depth to which you fall, however, it states that the minimum safe depth for any dive is 30' (or less, for lesser dives) so I presume one would go no deeper than that.

[Talya]

Terminal velocity for concrete or even solid steel (if you're lucky enough to find something big enough made of steel to fall on ) is nowhere near that of the water's.

The phrase "terminal velocity" doesn't mean what you think it does. Safe to say, terminal velocity is always the same for any given object at a certain atmospheric pressure regardless of what substance you're going to land on.

Terminal Velocity is the speed at which an object stops accellerating during a freefall. For a human being, this is generally between 120mph (belly-to-ground skydiving) and 200mph (intentionally minimizing drag surface and aiming at the ground head or feet-first.)

Terminal Velocity has nothing to do with the speed at which a sudden stop is fatal.

[Big Fau]

Really? Care to explain why anti-tank bullets made from substances considerably harder than steel fragment, ricochet or break up when fired into water? Do you have an idea how much energy you need to pump into fluids to make them move once you exceed certain barriers (such as sound of speed in a given fluid) when displaced by object hitting the water to get the fluid to move?

Surface tension has nothing to do with it, fluid physics do.

Fact: Water is not harder than concrete. Just easier to move through. The rapid deceleration is actually what causes bullets and tank shells to disintegrate.


Mythbusters busted this fairly recently. Falling on concrete at terminal velocity resulted in a pig corpse getting decapitated, whereas the water merely broke the neck (the head was still attached).

[Knaight]

Mythbusters busted this fairly recently. Falling on concrete at terminal velocity resulted in a pig corpse getting decapitated, whereas the water merely broke the neck (the head was still attached).

Which stands up as regards humans. However, if falling faster than the speed of sound in water, things get a lot messier, as the water can't really move out of the way effectively.

[Bhaakon]

Which stands up as regards humans. However, if falling faster than the speed of sound in water, things get a lot messier, as the water can't really move out of the way effectively.

Mythbusters did that one too, confirming your assertion. High-speed rifle bullets disintegrated into harmless shards near the surface, while slower shotgun slugs and handgun bullets held their shape and penetrated much farther.

[excruciarch]

as the water can't really move out of the way effectively.
Something hard monocrystalline will *move out of the way* with even less effectiveness, believe me. Comparing liquid water to something of solid state and high density is just wrong. The only thing that matters in this regard is kinetic energy loss after an object at given speed *meets* the surface of an other substance (or environment, don't know what exactly you call the process of an object leaving one environment (air) and entering the other (water)).
PS
A bullet will lose less energy entering water, but since water is in liquid state there is nothing to keep the bullet together if the impact damages bullet's structure. Then our bullet will just get *disintegrated* or *dispersed*. Given high enough speed and right angle it can even ricochet.