Earlier today my players found some Dust of Dryness. As our setting has Renaissance firearms, one of my players immediately asked if he could fire one of the pellets from a musket. I said he could try it, knowing that would give me until next week to come up with an answer.
I'm thinking this could go one of two ways: The pellet hits the target and disgorges the water, as my players are expecting, or, the pellet breaks inside the gun from the act of firing it and disgorges the water inside the gun.
For the first one, I'd probably say there's a knock back and it renders the target prone, but I'm not clear how to derive the damage.
For the second, I figure the gun is built to take an explosive internal pressure and channel it forward, since that's what a gun usually does. You've basically got a lethal-power water gun then. Still not sure how to derive that damage. Also, just out of curiosity, I got to thinking about what happens when you eject 15 cubic feet of water out of the muzzle of a gun. For ease of math, treat that as a contiguous series of 1 inch water cubes. If you put those in a line that works out to about 97200 squares on a battlemap. I don't think there's any way to tell if it has the energy to eject a line that length, since we don't have a real way to know how much force is exerted by the magical transformation. The same issue exists for trying to come up with realistic damage. I know we don't need to be realistic, but it's fun.
And than there's the issue of weather or not to allow other liquids...
If your players want the ability to soak something at long range, then allow it and see what creative uses they can make of that.
If they just want to do extra damage, that's boring. If they're rules lawyering the laws of physics and arguing it hurts real bad to be hit by a bullet-speed mass of multiple cubic feet of water, then push back that attempting to launch such a mass out of a gun is also impossible.
Same thing for people who try to enlarge/reduce something after launching it from a catapult. I'd be like, "Conservation of momentum, it slows to a crawl and drops straight down."
I'd say it does normal damage for the weapon plus unleashes the water on the target. Or maybe even 0 damage and just unleashes the water.
Rule of cool is the law, but cool is cooler if it can be built from the threads of reality, so I'm looking to reality as well. Plus, it's fun to figure out the physics.
I agree. I’d make it do the same damage that the firearm normally does and add soaking the target, putting out all fires in a 15’ radius of the target, as a secondary effect for fun.
I only have vague recollections of high school level physics ages ago so I am just going to hit this with broad strokes as best as I remember.
The law of conservation of energy (and/or conservation of momentum) says that energy going in is equal to the energy coming out. Because this is explosive acceleration the energy when the pellet is fired has to be equal or greater to the energy the pellet has at impact (some will be lost to air resistance). Therefore, if the pellet has enough energy to break at impact it should have had enough energy to break at launch. (Note: this specifically applies to explosive acceleration, a more gradual acceleration like a sling might still work. This is the difference between hitting the gas until your car reaches 90 miles per hour vs loading it in a cannon with enough TNT to accelerate it to 90 miles per hour).
On the other hand, physics still isn't on your side if the pellet breaks when the gun is fired. Water doesn't like to be compressed and will attempt to expand in all directions. Even a modern firearm wouldn't survive that level of pressure, a Renaissance era musket is just going to explode. Even if you were lucky enough for all the water to come out the front, the same force that it hitting the target is pushing the character with the gun backwards.
Now, on a side note: if one were to drop a pellet or two inside a scroll case full of nails you might have just invented a frag grenade. Just be careful not to jostle it too much before you throw it.
EDIT: regarding other liquids, the description specifically says water so I would only allow water. A possible reasonable stretch would be to use the dust of dryness to remove the water from something and concentrating what was left behind. Sprinkling dust of dryness over ale or wine might instantly distill it into a liquor.
The pellet would certainly shatter inside the barrel. This will release roughly 250,000 lb of water. Let me reiterate: two hundred and fifty thousand pounds of water. Not 15 cubic feet, 15x15x15=3375 cubic feet. If that happens instantly, that musket is gone and the shooter will quite probably be dead, unless they're so fortunate that the pieces of the weapon expelled towards them all miss any vital parts of their body and the explosive pressure fails to do them in as well. That's a lot to hope for.
Now, that's not really fun or cool to happen to a PC (maybe a little, it'd make for a memorable death at least), so I'd tone down the rate of expansion of the water. But at that point you're pretty much deciding what happens regardless of physics, so you might as well just go with whatever you think is best.
Magic violates the laws of physics in so many ways, I just don't see the point of trying to apply physics when magic items or spells are involved. If you are applying physics strictly, does the pellet have the mass of all the water in it? You couldn't even lift it.
Magic violates the laws of physics in so many ways, I just don't see the point of trying to apply physics when magic items or spells are involved. If you are applying physics strictly, does the pellet have the mass of all the water in it? You couldn't even lift it.
The pellet's weight is negligible, according to the spell description. The water's, as soon as the pellet is shattered, is definitely not.
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Honestly? In terms of “what would really happen,” my instinct is that it would destroy the firearm and drench the shooter and everything around them with (15m)³ of water. I’d say a Strength save or be knocked prone. This is my “best attempt at realism” ruling.
In terms of “rewarding a cool idea,” launching the pellet is far more believable to me than shooting a jet of water. There’s just no way the gun’s barrel is strong enough to redirect the water instead of just exploding. So for “rule of cool,” my ruling would be to simply allow the pellet’s normal effect but at long range; i.e. the pellet shatters exactly as it would if someone had used their action to do it locally, but it can happen at... up to the gun’s normal range, I guess?
Since the magic item doesn’t say anything about damage or knockdown effects, I wouldn’t say there are any. Pavilionaire’s point about conservation of momentum is very relevant here: when it leaves the gun, it has no mass, which means it has no momentum. To preserve that property, its velocity has to drop to zero when it suddenly acquires mass, so no damage.
It’s cool enough letting players activate the item at range. There’s no need to add damage or other effects to it beyond what the item’s description says.
**Snip** Pavilionaire’s point about conservation of momentum is very relevant here: when it leaves the gun, it has no mass, which means it has no momentum. To preserve that property, its velocity has to drop to zero when it suddenly acquires mass, so no damage.**Snip**
As long as we are getting deep in the physics, I am going to ague this point. The pellet's weight is 'negligible', which is not the same as having no mass. It just means it doesn't weigh enough to count against encumbrance. The weight of a single bullet in game terms is also negligible, but it certainly has enough mass to carry momentum.
However, I would argue that the momentum of the of the pellet has no effect on the water that magically reappears when the pellet shatters. Getting hit by that pellet is going to hurt, and then you find yourself drenched in a 15 foot cube of water.
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... And you really think that conservation of momentum or even energy has a sense in a universe where matter is created, with or without momentum, with magic all over the place ?
Real World physics only apply at the very basic level in D&D, there are so many spells and abilities (not to mention settings, with Spelljammer gravity being official in WD-DotMM) that break them completely.
At this stage, only Rule of Cool can really apply, with the only concern being making it not too overpowered.
Yes actually, I generally do.
1st: OP specifically was asking (in 3rd post) for how the real world physics would work, so a discussion of real world physics is entirely on topic here.
2nd: At the tables I play at things tend to work Like Reality Unless Noted. The only magic affecting the scenario is the the water pellet from the dust of dryness, and it is only magic in that when it shatters it brings back the water used to create it. From the limited description of the negligible weight marble sized pellet I don't see anything that would suggest that it would behave in any unexpected way.
Rule of Cool and Rule of DM absolutely do apply if that is what the DM wants to do with this, but for the moment we are talking physics.
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If the pellet explodes in the chamber, rather than just having the gun explode why not have a brief water cannon effect out of the barrel as all the water escapes?
Certainly I'd allow it to knock back, and end prone if you're closer to the gun. But no direct damage from the water (but if the enemy were standing near the edge of a cliff...)
(Quick google says water cannon shoots 20 litres of water per second.)
I would say the attacked creature takes 2d6 bludgeoning damage, and then both the attacker and the attacked make Strength saving throws, the attacker with a lower DC, or be knocked prone.
I would say the attacked creature takes 2d6 bludgeoning damage, and then both the attacker and the attacked make Strength saving throws, the attacker with a lower DC, or be knocked prone.
Why use the attacker's Strength for a musket shot?
I would say the attacked creature takes 2d6 bludgeoning damage, and then both the attacker and the attacked make Strength saving throws, the attacker with a lower DC, or be knocked prone.
Why use the attacker's Strength for a musket shot?
Because the explosion which would propel a bullet instead breaks the pellet, creating the effect of a fireman's hose, which by the way requires multiple people to hold on to because of its sheer water pressure.
I like the hose wrangling mechanics idea, but my "realism" sense floods the shooter. If you allow the munition to deliver the flood to the target on impact with target, Dust of Dryness is uncommon, so expect the future of warfare in your game to get literally bogged down by this tactical innovation with things like sieges being resolved by waterball munitions producing let's call it "explosive liquefaction" and the like; and dust of dryness is your game world's uranium. Just came here to drop the puns.
There's no way a small marble, which is designed to break, would survive the pressure of a gunpowder detonation. Then it turn there is no way a gun would survive the massive expansion of water within it. But the other thing to consider is the size of the marble. If its a couple of millimetres too large it won't fit down the barrel, while too small and it rattles around inside the gun and would tumble causing the pallet to break.
If the character is proficient in firearms then I would say he would understand the device well enough to know it wouldn't work. If he's not proficient then perhaps an int check to figure out the likely physical result.
I like the hose wrangling mechanics idea, but my "realism" sense floods the shooter. If you allow the munition to deliver the flood to the target on impact with target, Dust of Dryness is uncommon, so expect the future of warfare in your game to get literally bogged down by this tactical innovation with things like sieges being resolved by waterball munitions producing let's call it "explosive liquefaction" and the like; and dust of dryness is your game world's uranium. Just came here to drop the puns.
This is a great example of why I really dislike the game's rarity system for magical items. It feels like no one understands what 'common' or 'uncommon' mean as words.
Again one does not need this work with a firearm to be an issue. It could be fired from a sling with negligible risk of breaking on launch. It could be dropped from the air. It could be dropped en masse.
Sure, but it wouldn't be a very effective form of warfare, because the item does no damage and has no negative effect other than making stuff wet.
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Earlier today my players found some Dust of Dryness. As our setting has Renaissance firearms, one of my players immediately asked if he could fire one of the pellets from a musket. I said he could try it, knowing that would give me until next week to come up with an answer.
I'm thinking this could go one of two ways: The pellet hits the target and disgorges the water, as my players are expecting, or, the pellet breaks inside the gun from the act of firing it and disgorges the water inside the gun.
For the first one, I'd probably say there's a knock back and it renders the target prone, but I'm not clear how to derive the damage.
For the second, I figure the gun is built to take an explosive internal pressure and channel it forward, since that's what a gun usually does. You've basically got a lethal-power water gun then. Still not sure how to derive that damage. Also, just out of curiosity, I got to thinking about what happens when you eject 15 cubic feet of water out of the muzzle of a gun. For ease of math, treat that as a contiguous series of 1 inch water cubes. If you put those in a line that works out to about 97200 squares on a battlemap. I don't think there's any way to tell if it has the energy to eject a line that length, since we don't have a real way to know how much force is exerted by the magical transformation. The same issue exists for trying to come up with realistic damage. I know we don't need to be realistic, but it's fun.
And than there's the issue of weather or not to allow other liquids...
Rule of cool is more important than physics here.
If your players want the ability to soak something at long range, then allow it and see what creative uses they can make of that.
If they just want to do extra damage, that's boring. If they're rules lawyering the laws of physics and arguing it hurts real bad to be hit by a bullet-speed mass of multiple cubic feet of water, then push back that attempting to launch such a mass out of a gun is also impossible.
Same thing for people who try to enlarge/reduce something after launching it from a catapult. I'd be like, "Conservation of momentum, it slows to a crawl and drops straight down."
I'd say it does normal damage for the weapon plus unleashes the water on the target. Or maybe even 0 damage and just unleashes the water.
Rule of cool is the law, but cool is cooler if it can be built from the threads of reality, so I'm looking to reality as well. Plus, it's fun to figure out the physics.
I agree. I’d make it do the same damage that the firearm normally does and add soaking the target, putting out all fires in a 15’ radius of the target, as a secondary effect for fun.
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Physics is a cruel mistress..
I only have vague recollections of high school level physics ages ago so I am just going to hit this with broad strokes as best as I remember.
The law of conservation of energy (and/or conservation of momentum) says that energy going in is equal to the energy coming out. Because this is explosive acceleration the energy when the pellet is fired has to be equal or greater to the energy the pellet has at impact (some will be lost to air resistance). Therefore, if the pellet has enough energy to break at impact it should have had enough energy to break at launch. (Note: this specifically applies to explosive acceleration, a more gradual acceleration like a sling might still work. This is the difference between hitting the gas until your car reaches 90 miles per hour vs loading it in a cannon with enough TNT to accelerate it to 90 miles per hour).
On the other hand, physics still isn't on your side if the pellet breaks when the gun is fired. Water doesn't like to be compressed and will attempt to expand in all directions. Even a modern firearm wouldn't survive that level of pressure, a Renaissance era musket is just going to explode. Even if you were lucky enough for all the water to come out the front, the same force that it hitting the target is pushing the character with the gun backwards.
Now, on a side note: if one were to drop a pellet or two inside a scroll case full of nails you might have just invented a frag grenade. Just be careful not to jostle it too much before you throw it.
EDIT: regarding other liquids, the description specifically says water so I would only allow water. A possible reasonable stretch would be to use the dust of dryness to remove the water from something and concentrating what was left behind. Sprinkling dust of dryness over ale or wine might instantly distill it into a liquor.
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The pellet would certainly shatter inside the barrel. This will release roughly 250,000 lb of water. Let me reiterate: two hundred and fifty thousand pounds of water. Not 15 cubic feet, 15x15x15=3375 cubic feet. If that happens instantly, that musket is gone and the shooter will quite probably be dead, unless they're so fortunate that the pieces of the weapon expelled towards them all miss any vital parts of their body and the explosive pressure fails to do them in as well. That's a lot to hope for.
Now, that's not really fun or cool to happen to a PC (maybe a little, it'd make for a memorable death at least), so I'd tone down the rate of expansion of the water. But at that point you're pretty much deciding what happens regardless of physics, so you might as well just go with whatever you think is best.
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Magic violates the laws of physics in so many ways, I just don't see the point of trying to apply physics when magic items or spells are involved. If you are applying physics strictly, does the pellet have the mass of all the water in it? You couldn't even lift it.
The pellet's weight is negligible, according to the spell description. The water's, as soon as the pellet is shattered, is definitely not.
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Honestly? In terms of “what would really happen,” my instinct is that it would destroy the firearm and drench the shooter and everything around them with (15m)³ of water. I’d say a Strength save or be knocked prone. This is my “best attempt at realism” ruling.
In terms of “rewarding a cool idea,” launching the pellet is far more believable to me than shooting a jet of water. There’s just no way the gun’s barrel is strong enough to redirect the water instead of just exploding. So for “rule of cool,” my ruling would be to simply allow the pellet’s normal effect but at long range; i.e. the pellet shatters exactly as it would if someone had used their action to do it locally, but it can happen at... up to the gun’s normal range, I guess?
Since the magic item doesn’t say anything about damage or knockdown effects, I wouldn’t say there are any. Pavilionaire’s point about conservation of momentum is very relevant here: when it leaves the gun, it has no mass, which means it has no momentum. To preserve that property, its velocity has to drop to zero when it suddenly acquires mass, so no damage.
It’s cool enough letting players activate the item at range. There’s no need to add damage or other effects to it beyond what the item’s description says.
I don’t know if it would be physically possible, but i would rule it canon. It’s pretty creative thinking
As long as we are getting deep in the physics, I am going to ague this point. The pellet's weight is 'negligible', which is not the same as having no mass. It just means it doesn't weigh enough to count against encumbrance. The weight of a single bullet in game terms is also negligible, but it certainly has enough mass to carry momentum.
However, I would argue that the momentum of the of the pellet has no effect on the water that magically reappears when the pellet shatters. Getting hit by that pellet is going to hurt, and then you find yourself drenched in a 15 foot cube of water.
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Yes actually, I generally do.
1st: OP specifically was asking (in 3rd post) for how the real world physics would work, so a discussion of real world physics is entirely on topic here.
2nd: At the tables I play at things tend to work Like Reality Unless Noted. The only magic affecting the scenario is the the water pellet from the dust of dryness, and it is only magic in that when it shatters it brings back the water used to create it. From the limited description of the negligible weight marble sized pellet I don't see anything that would suggest that it would behave in any unexpected way.
Rule of Cool and Rule of DM absolutely do apply if that is what the DM wants to do with this, but for the moment we are talking physics.
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If the pellet explodes in the chamber, rather than just having the gun explode why not have a brief water cannon effect out of the barrel as all the water escapes?
Certainly I'd allow it to knock back, and end prone if you're closer to the gun. But no direct damage from the water (but if the enemy were standing near the edge of a cliff...)
(Quick google says water cannon shoots 20 litres of water per second.)
I would say the attacked creature takes 2d6 bludgeoning damage, and then both the attacker and the attacked make Strength saving throws, the attacker with a lower DC, or be knocked prone.
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Why use the attacker's Strength for a musket shot?
Because the explosion which would propel a bullet instead breaks the pellet, creating the effect of a fireman's hose, which by the way requires multiple people to hold on to because of its sheer water pressure.
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I like the hose wrangling mechanics idea, but my "realism" sense floods the shooter. If you allow the munition to deliver the flood to the target on impact with target, Dust of Dryness is uncommon, so expect the future of warfare in your game to get literally bogged down by this tactical innovation with things like sieges being resolved by waterball munitions producing let's call it "explosive liquefaction" and the like; and dust of dryness is your game world's uranium. Just came here to drop the puns.
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There's no way a small marble, which is designed to break, would survive the pressure of a gunpowder detonation. Then it turn there is no way a gun would survive the massive expansion of water within it. But the other thing to consider is the size of the marble. If its a couple of millimetres too large it won't fit down the barrel, while too small and it rattles around inside the gun and would tumble causing the pallet to break.
If the character is proficient in firearms then I would say he would understand the device well enough to know it wouldn't work. If he's not proficient then perhaps an int check to figure out the likely physical result.
I'm liking the world of waterlogged warfare this thread inspired in me. I may run with it, with squishy shoes.
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Sure, but it wouldn't be a very effective form of warfare, because the item does no damage and has no negative effect other than making stuff wet.