Physics Question D&D

[Silva Stormrage]

So a random idea popped into my mind. Imagine you set up a box of permanency walls of force so that there was a roof, bottom and all 4 walls. Then set up a teleportation circle to go inside the box. Then set up 10-20 decanters of endless water to go into the box. What would happen? I am not the best at this sort of physics so I am not sure what would happen to the water.

Would the clause of teleportation that states you have to teleport objects into a space that can support it apply?

If you could make it so that the water continually goes into the box that can't expand or break for about a year or so. Then disintegrate or destroy a wall of force what would happen? Is this effectively a mini bomb?

[Deophaun]

No real idea on the teleportation, but with the "mini-bomb," as the best a decanter of endless water can do is emit a geyser, the water in the box is effectively incompressible. There's simply not enough pressure being generated. When you disintegrate one of the walls, all the will happen is the water will spill out and you'll have 10-20 water-powered rockets take off.

[Silva Stormrage]

No real idea on the teleportation, but with the "mini-bomb," as the best a decanter of endless water can do is emit a geyser, the water in the box is effectively incompressible. There's simply not enough pressure being generated. When you disintegrate one of the walls, all the will happen is the water will spill out and you'll have 10-20 water-powered rockets take off.

No I think I was probably unclear then. I meant what would happen if you put about a years worth of the water produced from the decanters into a 10 by 10ft box covered on all sides by walls of force. Then destroy a wall. I imagine the water being that tightly compressed would expand outward as a years worth of water (About 157680000 gallons per decanter unless I screwed up somewhere mathematically) and fill it's normal volume. Unless of course water being that tightly compressed changes some of it's properties.

[Zaq]

You're applying physics to something involving walls of force. At the very best, whatever you come up with will have terrible implications that could have very bad ramifications across the system if applied in a general sense.

Tread. With. Care.

[Deophaun]

You were clear. The water simply wouldn't go into the box. The most pressure a decanter of endless water can produce creates a measly geyser that a person can overcome with an easy Strength check. That's not enough force to push more water into a space that is already full. You need the pressure equivalent of the deep ocean to do that. Your decanters will just sit there, unable to empty their contents for a year.

Edit: If, however, they did manage to put all their water into that little box, you wouldn't have water anymore. You'd have a quantum singularity due to all that mass being concentrated in that tiny space. At that point, you have a sphere of annihilation that pops the walls of force automatically.

[Ninjadeadbeard]

No I think I was probably unclear then. I meant what would happen if you put about a years worth of the water produced from the decanters into a 10 by 10ft box covered on all sides by walls of force. Then destroy a wall. I imagine the water being that tightly compressed would expand outward as a years worth of water (About 157680000 gallons per decanter unless I screwed up somewhere mathematically) and fill it's normal volume. Unless of course water being that tightly compressed changes some of it's properties.

Water's incompressible. If I understand that correctly, the decanters would just stop filling the box because the pressure wouldn't allow more water into the box. Like Deophaun said.

[Mnemnosyne]

The logical answer for the decanter part is that the decanters would stop pouring when the water pressure inside the sealed box reaches the point where the water itself is equivalent to a stopper. Not sure how many PSI that amounts to, but it's probably not a lot.

[Silva Stormrage]

You were clear. The water simply wouldn't go into the box. The most pressure a decanter of endless water can produce creates a measly geyser that a person can overcome with an easy Strength check. That's not enough force to push more water into a space that is already full. You need the pressure equivalent of the deep ocean to do that. Your decanters will just sit there, unable to empty their contents for a year.

Ah in that case I would wonder why the water would't go in as the water is being magically teleported in and since teleportation circle is not a two way effect the water can't spill back out.

Or better yet, what would happen if I managed to make a spell that WOULD let the water enter that small of a space.

[Siosilvar]

Couple options.

1) The water doesn't teleport. Since there's already stuff there, and you can't teleport into something else, it simply doesn't happen.
2) For the same reasons as above, the water gets teleported to the outside of the walls, like when you try to dimension door into solid rock. It takes 1d6 damage, if that means anything to water.
3) A wall of force breaks. After all, it takes only a DC 120 Escape Artist check to get through, so a comparable Strength check should do about the same.
4) You get a black hole.

[Slipperychicken]

The Decanters, even if the water-flow didn't care about water pressure, would break under sufficient pressure. Some kind of one-way Gate to the elemental plane of water would be better for this idea.


Check out Riverine. It's a material from Stormwrack; water sandwiched between walls of force. It's similar to what you're describing here.

[killianh]

Couple options.

1) The water doesn't teleport. Since there's already stuff there, and you can't teleport into something else (at least in 3.5; you get pushed to the nearest available space), it simply doesn't happen.
2) For the same reasons as above, the water gets teleported to the outside of the walls, like when you try to dimension door into solid rock. It takes 1d6 damage, if that means anything to water.
3) A wall of force breaks. After all, it takes only a DC 120 Escape Artist check to get through, so a comparable Strength check should do about the same.
4) You get a black hole.

basically this. If you did have a form of spell that you placed inside the cube that endlessly spouted water (maybe a trap of create water activated by being near a wall of force?) then it would build up PSI until it could emulate a DC 120 strength check.

A car with say 1550 lbs is held up by 4 35 PSI tires which is a max load on some cars. For easy math (though will probable be wrong in actual physics) would be to say that 140 PSI can hold 1550 lbs up or roughly the top load D&D 3.5 heavy load for a 30 STR character. If it would take a DC 120 break check to break a wall of force then it would need to reach a psi of 560 to blow a wall, at which point the speed and flow of the water would follow normal physics for rupture of high pressure containers (which I don't have the math equation on hand for)

on the plus side the smaller the box the more deadly the pop so this could be weaponized with a custom magic item :smallamused:

EDIT: The math might be off a bit further than expected due to the fact that weight limits are based both on size and strength and I've only accounted for weight. If the tires used the example are called small creatures than PSI would be 1120 needed. If the water is considered a large creature than the psi is only 280 (as best as my math ATM is allowing me to calculate

[Snowbluff]

You're applying physics to something involving walls of force. At the very best, whatever you come up with will have terrible implications that could have very bad ramifications across the system if applied in a general sense.

Tread. With. Care.

This. This, so very hard.

Last time I checked, [Force] shouldn't work like it does. :smalleek:

[Mithril Leaf]

This. This, so very hard.

Last time I checked, [Force] shouldn't work like it does. :smalleek:

Yeah, that is quickly discovered in just about every thread that discusses anything made of force. It does count as a material though.

[demigodus]

Well, the decanter isn't exactly pouring water in, as it is making water out of no where, and lightly pushing it in there. If we take that interpretation, then the volume of the water will keep increasing. The decanter just will have trouble getting a sufficient force to push said water out of itself (until it builds up, then pushes out?).

As for the actual physics, if water was incompressible, trying to put more water in there would create infinite pressure. Which, strangely enough isn't what would happen. To help explain the situation, a 2D phase diagram (http://en.wikipedia.org/wiki/Phase_diagram) is probably the simplest scientific diagram I know of for this. Here is the image in question:
http://en.wikipedia.org/wiki/File:Phase-diag2.svg

Now, it has been around 4 years since I have used a phase diagram, but based on what the image shows, apparently there IS a pressure at which liquids become compressible again. In that case, as the wall of force gets completely filled, the moment another drop is added, the area around that drop would shoot up in pressure until the water got compressible again. And eventually the entire thing would turn into a compressible liquid.

So if you managed to teleport water into water, then yes, you would end up with compressible water. That is a bomb when you disable the walls. Except at this point, it would be reasonable to demand that what a wall of force does be explained in more precise, physics terms.

[demigodus]

basically this. If you did have a form of spell that you placed inside the cube that endlessly spouted water (maybe a trap of create water activated by being near a wall of force?) then it would build up PSI until it could emulate a DC 120 strength check.

A car with say 1550 lbs is held up by 4 35 PSI tires which is a max load on some cars. For easy math (though will probable be wrong in actual physics) would be to say that 140 PSI can hold 1550 lbs up or roughly the top load D&D 3.5 heavy load for a 30 STR character. If it would take a DC 120 break check to break a wall of force then it would need to reach a psi of 560 to blow a wall, at which point the speed and flow of the water would follow normal physics for rupture of high pressure containers (which I don't have the math equation on hand for)

That PSI is a measure of how much pressure the strength of the tires (as in, how much pressure breaks them). You can't convert that PSI into a force it is lifting though. Using a different cart design, you might, after all, end up with tires that are under more PSI of pressure while holding up the same load.

Also, 3.5 strength-to-weight are exponential, not linear. So if a 30 STR is 1,600lb (value calculated from the SRD), then 120 STR would correspond to 1,600lb * 4^9 = 419,430,400lb of force.

Because the way 3.5 works, this force is applied to a 5ftx5ft square area, or 3600 square inches of area. That comes out to ~116,508 PSI.

[Twilightwyrm]

I think in this case it would be helpful to think of walls of force as functionally equivalent to the magnetic fields generated by super-powerful magnets that can sometimes be used in science to test things like, say, plasma. That being said, the way you describe it, I'm inclined to agree with this option:
"2) For the same reasons as above, the water gets teleported to the outside of the walls, like when you try to dimension door into solid rock. It takes 1d6 damage, if that means anything to water."
I would also echo that warning that has been mentioned here about applying physics to walls of force. I have given a general description of a real-world analogue, but even this is inaccurate at best.

[sonofzeal]

If water was uncompressible, sound could not propagate through it. Since common experience informs us that it actually propagates much better than in air, this is obviously mistaken. A cursory google search informs me that the compressibility of water is roughly that of steel. Water under sufficient pressure will start generating heat, but that's another issue.

Really, I think the weak spot here is the teleportation. Can you teleport something somewhere that's already "full"? Probably not. Air displacement is taken for granted, but I don't think you can teleport a liquid to where a liquidalready is, just like you can't teleport a solid to where a solid already is.

[NichG]

The teleportation is definitely the weak spot of this argument.

If you just had the decanters inside the area, I'd say they either get stoppered or more likely, they're eventually damaged and destroyed by the pressure (at deep sea environments there's pressure damage in D&D, and a decanter of endless water doesn't have many HP). So you'd get a decently pressured water bomb, but not some kind of singularity (and honestly, a year's worth of water production isn't enough to make a singularity with an event horizon big enough to be observed. The entire mass of the Earth only gives you something like a 1cm event horizon. You'd get a highly compressed plasma, maybe neutron-star density if you're lucky.

So lets see... 20*30 gallons per 6 seconds is about 380kg/sec, so for a year that's 1.2*10^10 kg. Neutron stars are roughly 10^18 kg/m^3, so if you wanted this to even hit neutron star densities you'd need to confine it into a cubical volume a few millimeters to a side. So you're pretty much still going to be in the realm of 'ordinary' plasmas if you're working in 5ft squares.

Actually you might just end up with a solid phase of water. It depends on the radiative cooling rate through the walls of force, whether or not the thing can cool down fast enough to solidify.

[ericgrau]

It would build up to geyser pressure then stop flowing. Which is basically instantly after the box fills up since the water is almost incompressible. For the same reason the moment you remove a wall or open a teleportation outlet it would almost instantly relieve the pressure and the water would not geyser out. It would flow out gently and it would only geyser the normal amount from the decanters.

It takes thousands of psi to crush a solid (not hollow) object. In some cases a solid object would never break. The decanters would not break.

So all in all the effect would be pretty underwhelming. A splash of water spills gently out of your teleport destination, then a smaller waterfall continues from there.

[Dusk Eclipse]

Won't someone think of the poor catgirls?:smalleek:

Someone had to do it

[The Dark Fiddler]

I can't speak as though I'm an expert at physics, having only taken a high-school level course, but I can say what I'd do as a DM if somebody tried this in a game I was running. I'd let the decanters fill up the box, and once that happens, I'd have the decanters push themselves away from the portal they're filling. If they were suspended above the portal, I'd just treat it as though the portal was the surface of the water, meaning it would start filling whatever room you set the teleportation circle in instead.

Funny enough, looking up the spell made me realize that you can't actually do this, as teleportation circle only works on creatures who activate it. I'm ignoring that and assuming some sort of mostly-equivalent ability for the sake of argument, however.

[KoopaTrooper#12]

Water can be compressed it just takes a lot of pressure, it creates different forms of ice like Ice 7.

Now you are using a decanter of endless water what if you did it differently, use dust of dryness. Put a wall of force around a bunch of dust of dryness beads that have already absorbed water and then rupture them. The water doesn't flow out like a decanter all the volume is released. So you would get way more water then there is room for.

I think it would become a form of ice (like ice 7) from the extreme pressure but would quickly shatter the wall of force much like a legendary dreadnought can with a strength check (DC: 32) and as the wall breaks the water would no longer be under pressure and would go back to a more natural form. If someone happened to be inside the wall of force with the beads of dryness (full of water) when they were broken.. I think that person is way beyond dead.

[Zale]

So, you can't teleport something into water?

[Ashtagon]

Won't someone think of the poor catgirls?:smalleek:

Someone had to do it

This. Exactly this. We both had to do it.

[Andvare]

A water diagram.

http://www.lsbu.ac.uk/water/phase.html

[Anxe]

The simplest interpretation by RAW is that the box is full, so the water is teleported out of the space.

If we're looking for a physics question, wouldn't the water in the box vaporize? It slowly fills up the box, causing the air to be more and more pressurized. This pressurizes the water more, allowing it to enter the gas phase (or supercritical fluid, whatever). I think this would allow even more water to be pumped in over time, eventually turning the contents of the box into plasma. We could say that plasma dissolves the walls of force, but the game already has rules for plasma (or similar things) in the DMG futuristic weapons. Those only deal damage which does not affect a wall of force.

So now the water starts doing fusion reactions within the wall of force. Heat starts to be transferred through the walls. Massive amounts of heat. The heat would dissipate though. I guess this would cause significant warming within the area around the box.

If you dispel the box you'd get a fusion meltdown reaction of some kind. I'm not sure what that affect would be, but it'd be like a nuclear bomb.

[Anxe]

So, you can't teleport something into water?

More specifically, you can't teleport something into a space where there is no room for expansion. If I teleport someone into a lake, the lake's surface goes up by a millimeter or something. But if I teleport them into a box of water from which the water cannot escape... That would be just like teleporting someone into a stone wall. They can't go there, so the spell shunts them off in some direction.

[Deophaun]

If water was uncompressible, sound could not propagate through it.
Actually, sound would propagate through it at infinite speed, which breaks the laws of physics. So, matter is always compressible.

[Slipperychicken]

More specifically, you can't teleport something into a space where there is no room for expansion. If I teleport someone into a lake, the lake's surface goes up by a millimeter or something. But if I teleport them into a box of water from which the water cannot escape... That would be just like teleporting someone into a stone wall. They can't go there, so the spell shunts them off in some direction.

If teleporting into open water displaces the water, why wouldn't teleporting into stone displace it as well?

[Ravenica]

because stone isn't a fluid and doesn't utilize fluid dynamics

[Yora]

Actually, sound would propagate through it at infinite speed, which breaks the laws of physics. So, matter is always compressible.
At the very least when the pressure gets high enough to make the sub-atomic particles turn into neutron star matter.

Assuming water were incompressible, you would fill the space with as much water molecules as it can hold, and to get one more molecule inside, you need to push it with enough force to make the entire water turn into neutron star matter. And I don't have a number, but "ginormous" sounds like a good approximation.

[Deophaun]

because stone isn't a fluid and doesn't utilize fluid dynamics
Careful, I believe sand utilizes FD as well. Let's just leave it as "'cause the books say so."

At the very least when the pressure gets high enough to make the sub-atomic particles turn into neutron star matter.
Even that is compressible. The degenerate matter at the surface of a neutron star is less dense than the degenerate matter at the center.

[TelemontTanthul]

First: I am assuming that the decanters are inside of this "Cube of Force".

Second: I am assuming that the decanters magically create water, leaving nowhere for the water to exit.

That being said, I believe that the logical result would be that the decanters of water would succumb to the pressure long before the walls of force did.

Now: If the decanters are outside of the Cube of Force, then I wouldn't know what would happen.

[Zale]

More specifically, you can't teleport something into a space where there is no room for expansion. If I teleport someone into a lake, the lake's surface goes up by a millimeter or something. But if I teleport them into a box of water from which the water cannot escape... That would be just like teleporting someone into a stone wall. They can't go there, so the spell shunts them off in some direction.

That makes sense.

[Ravenica]

Careful, I believe sand utilizes FD as well. Let's just leave it as "'cause the books say so."

Even that is compressible. The degenerate matter at the surface of a neutron star is less dense than the degenerate matter at the center.

sand is a particulate in addition to being a solid, it does use FD, Ice utilizes plastic flow and thus obeys some of the laws of fluid dynamic, the only thing to fear is people trying to justify sillyness with bad science :smalltongue:

[NichG]

The simplest interpretation by RAW is that the box is full, so the water is teleported out of the space.

If we're looking for a physics question, wouldn't the water in the box vaporize? It slowly fills up the box, causing the air to be more and more pressurized. This pressurizes the water more, allowing it to enter the gas phase (or supercritical fluid, whatever). I think this would allow even more water to be pumped in over time, eventually turning the contents of the box into plasma. We could say that plasma dissolves the walls of force, but the game already has rules for plasma (or similar things) in the DMG futuristic weapons. Those only deal damage which does not affect a wall of force.

So now the water starts doing fusion reactions within the wall of force. Heat starts to be transferred through the walls. Massive amounts of heat. The heat would dissipate though. I guess this would cause significant warming within the area around the box.

If you dispel the box you'd get a fusion meltdown reaction of some kind. I'm not sure what that affect would be, but it'd be like a nuclear bomb.

It'd cool down pretty quickly honestly. Fusion is very picky, especially the kind of fusion you'd get with ordinary water (as opposed to deuterium water). This is basically the exact problem that we have with making actual fusion power plants that break even - things generally cool down the chamber, matter is lost to the walls, etc, and your efficiency shoots through the floor.

So I'm going to do a calculation to check this, because what the heck. Spoilered since it's going to be mathy.



The walls of force are transparent, so unlike the sun where lots of heat is retained due to photons taking millions of years to escape the core, this thing might cool down too fast to actually maintain fusion. To really say what'd happen we'd need an equation of state that models the water->supercritical fluid->plasma transition; we could use a vanderWaals fluid or something, but above critical an ideal gas is probably decent enough (at least until you need a relativistic gas). So PV=NkT. We also will need the ratio of specific heats, so lets assume that the water falls apart by the time we're interested so gamma=5/3 (monatomic gas).
We also need to assume a constraint on our inclusion of material, such as an adiabatic process or isothermal process.

So basically we're holding V constant, and changing N (and P and T by consequence). If we assume that we're doing this fast compared to the cooling mechanisms, we're changing things adiabatically, so: P^(-2/3) T^(5/3) = P0^(-2/3) T0^(5/3).

Taking P0 and T0 to be atmospheric pressure and a temperature of 300K, we have that:

T=300K * (P/1 atm)^(2/3)

But P=NkT/V and P0=N0 k T0/V0, so we can write this:

T = 300K * (N/N0)^2

We have dN/dt from the rate of inflow of water. Lets call this Q. For simplicity, lets write Q in terms of system volumes per unit time, so Q = (1/N0) dN/dt = constant. This also means that N = N0*Q*t.

We then have:

dT/dt = 300K * 2 * Q^2 * t

So the heating (assuming perfectly reflective walls of force instead of transparent) would go like T ~ 300 K * Q^2 * t^2, so it gets hot decently fast.

Now lets consider radiative cooling. If this is a cubical wall of force 1 meter to a side then we have a surface area of 6 m^2. This radiates at roughly 3x10^(-7) T^4 watts (for T in kelvin). So we know that at some point, radiative cooling will become faster than the compressive heating and the thing will stop getting hotter (barring fusion processes, self-gravitation, and the like). We can figure out this temperature, but we need the specific heat of our stuff. For a monoatomic ideal gas at constant volume, this is 3/2 R or about 10 J/mol K. The specific heat of our system will therefore be Cv=10*(N0/6*10^23)*(1+Q*t).

So what does this mean? The time derivative of the temperature from cooling will be dT/dt = -(1/Cv) sigma A T^4 (where sigma A = 3x10^(-7)). When this is equal to our heating term in size, we know we've left the adiabatic regime. That happens when:

3*10^(-7) * (6*10^23/N0)/(10*(1+Qt)) * (300 K)^4 * Q^8 t^8 = 300K * 2 * Q^2 * t

Our one meter cube contains about 2*10^5 moles of atoms when filled with water at STP, so we know N0. The inflow is 100 gallons/second (for 20 decanters), where a cubic meter of water is 264 gallons, so Q is about 0.4.

This gives us that the isothermal time is about 20 seconds, with a temperature around 20000K.

So this thing very very quickly heats up and then starts glowing white hot. Its radiating at 50 gigawatts, so this thing is very quickly heating up its environment. However, it can't get hotter unless it raises the exterior environment to a comparable temperature, and 20000K isn't enough to get fusion (it takes 14 million kelvin in the sun).


TLDR: The thing equilibriates at around 20000K, and doesn't end up hitting the requirements for fusion.

[Anxe]

Ah! Thank you! Still quite hot, but not fusion hot. Wanna do the math on the walls being dispelled?

[hoverfrog]

I believe that the logical result would be that the decanters of water would succumb to the pressure long before the walls of force did.Exactly what I was going to say. the pressure would build until the decanters could either no longer force water into the area or they were crushed by the pressure.

Is it actually possible to connect walls of force like this anyway? The caster can form the wall into a flat, vertical plane whose area is up to one 10- foot square per level. The wall must be continuous and unbroken when formed. If its surface is broken by any object or creature, the spell fails.Walls of force can be placed next to one another in a pattern but they aren't actually connected in a seamless way. Water would just escape through the gaps.