ok so physics question

[Ezekiel_Sar'run]

So say i have a homebrew race that applies a 10ft burst radius of pressure and that the character in questions pressure is 10 tons of weight, what kind of damage or effects would that have on the people around him? (hes excluded from the effect as the caster)

[Segev]

Well, first off, "pressure" is measured per-square-[area] of surface, typically. "Ten tons of pressure" is not meaningful as written, because if it's "ten tons per square mile," for instance, that's actually not very much pressure at all.

Standard atmospheric pressure is ~15 psi (pounds per square inch).

A mile is 5280 feet, or 63,360 inches on a side. A square mile (a square one mile on a side) is thus 4,014,489,600 square inches. 60,217,344,000 pounds per square mile is thus the atmospheric pressure of the Earth at sea level. That's 30,108,672 "tons of pressure," but it's distributed over a square mile.

A mere 10 tons-per-square mile would be 0.000005 pounds per square inch.

That's practically vacuum by our standards.

Assuming you mean 10 tons per square inch, that's 20000 psi, or 1,333 and 1/3 times the pressure that we experience from the atmosphere under normal circumstances.

According to a quick Google search, a human body (assuming it's breathing some sort of super-oxygenated fluid) can survive 100x the normal atmospheric pressure.

So, if you're talking 10 tons per square inch, pretty much everything is pulped, no save (except possibly "reflex negates" if they can get out of the area before the pressure wave hits them).

Now, if you're modeling it as a detonation pressure-wave, it might do less, but I haven't really studied the instantaneous pressures generated by various detonations.


Honestly, rather than calling it "ten tons of pressure," I'd call it "a high pressure field" and simply give it a number of dice of damage based on effective caster level. 1d6 per CL or 1d6/2 CL seems generally reasonable, depending on how easy it is to use. Fortitude for half, perhaps.

[Andvare]

He could mean a force of 10 tons applied to the neighbour squares, which would be something akind to 25 square feet per square (an approximation, a poor approximation), with 8 squares neighbouring a medium sized creature's square, that would be 200 square feet, so 28800 square inches. So (depending on which ton there is used), it would be 22400/28800 or 0.778 psi, or in other terms, a light breeze.

[ericgrau]

10 tons applied to a 10 foot radius is 20,000 pounds / (4 * pi * (10 ft.)^2 * (12 in./ft.)^2) = 0.11 psi.

It may be better to reconvert this into a force. An average person is about 1400 square inches on one side so that would be 150 pounds. That's roughly enough to accelerate somebody at 1 G, so treat it like sideways falling a short distance, dealing 1d6 damage. A size large creature would receive 600 pounds of force on his roughly 1200 pound body, so 0.5 G's and half the damage.

But it would have made more sense to define the effect in terms of however much damage you want and don't specify the tonnage. At least now you know it's reasonable to half/double the damage and knockback per size category of the foe.

Personally I like the "however much damage you want" option, with similar knockback. And then adjust it based on the size category of surrounding foes (half/double each). Dump a bag of cats on the guy and watch them fly and explode.

[Ezekiel_Sar'run]

ok so maybe this will help you answer my question better.

"Certain creatures emit a field of Spiritual Pressure that affect the mind and body..... the effect Spiritual weight has on the body shows that it emits what feels like actual pressure on the subjects. This pressure is greater depending on the creatures Spiritual Rank....works in an aura out to 10 ft. As a standard action (and as part of intimidate) you can surge your aura. While intimidating, there is an actual weight on the enemy...."
ok so my rank and level cause the pressure to be 19,800 lbs

[Chronos]

What book is this from? Because it still doesn't make sense.

[prufock]

Yeah, it sounds like a poorly thought out or poorly written homebrew rule. The closest I can think of is the falling damage (http://www.d20srd.org/srd/environment.htm#fallingObjects) rules.

For each 200#, the object deals 1d6, so 19800/200=99d6 damage, provided it falls at least 10 feet.

[Platymus Pus]

ok so maybe this will help you answer my question better.

"Certain creatures emit a field of Spiritual Pressure that affect the mind and body..... the effect Spiritual weight has on the body shows that it emits what feels like actual pressure on the subjects. This pressure is greater depending on the creatures Spiritual Rank....works in an aura out to 10 ft. As a standard action (and as part of intimidate) you can surge your aura. While intimidating, there is an actual weight on the enemy...."
ok so my rank and level cause the pressure to be 19,800 lbs

It sounds like a game of bleach.
What is that from?

[Dusk Eclipse]

It says right in the OP that it is a homebrewed race :smallsigh:

[Lightlawbliss]

-snip-

This doesn't help at all.

Lbs is a measure of mass iirc (I know it's mass or weight)

Presure is total force over area.

weight gives us force, we have no area.

[Platymus Pus]

It says right in the OP that it is a homebrewed race :smallsigh:

And I would like to know what race it is. It may help.

[ericgrau]

Well assuming 0.1 psi as found before, 0.1 psi on one side of a person would throw him back a little like a repelling shield. 0.1 psi surrounding him wouldn't be that noticeable. It might make his ears feel a little pressure like when you swim to the bottom of a swimming pool. So he'd notice it but it'd be harmless.

Again the ability is so arbitrary I don't see much point in measuring it with real world physics. Just use game measurements instead, like squares or hp damage or a demoralizing effect or whatever.

[Segev]

Okay. If what you're trying to do is impose weight on a character but not damage, what you do is simply take the "weight" your aura applies and make it so that all creatures in the aura are "carrying" that much extra weight. This will put most characters into the "you can't hold up this much" category, it sounds like. Check out the Encumberance rules.

[Autopsibiofeeder]

Well assuming 0.1 psi as found before, 0.1 psi on one side of a person would throw him back a little like a repelling shield. 0.1 psi surrounding him wouldn't be that noticeable. It might make his ears feel a little pressure like when you swim to the bottom of a swimming pool. So he'd notice it but it'd be harmless.

Again the ability is so arbitrary I don't see much point in measuring it with real world physics. Just use game measurements instead, like squares or hp damage or a demoralizing effect or whatever.

I agree. Perhaps the OP is looking for a Slow type effect, or being affected as if under water in terms of movement? (Am still not sure what the ability is supposed to do exactly).

[RaviStrife]

So say i have a homebrew race that applies a 10ft burst radius of pressure and that the character in questions pressure is 10 tons of weight, what kind of damage or effects would that have on the people around him? (hes excluded from the effect as the caster)

I think he's more looking for the effects of a "powerful presence" in game terms.

(Also, props to the person who got the Bleach reference. .. this definitely sounds like it.


In game terms, you'll likely want to represent this in a few different ways.
1) You'll likely need to create a subsystem similar to hardness-say the BBEG has "A powerful spiritual field-your weapons can't penetrate his skin"- treat it like he has a "Power Level" of 5; you have to Power Attack for 5 points of BaB to have any damage get through. Alternately, simply give him DR/- that scales base on the HD of the attacker (5 DR/- vs 1 level lower, 10 DR/- vs 2 levels lower, and so on)

2) For the character itself, you can represent this as a temporary exhaustion effect (specifically the strength and dexterity penalties), either based on a save or outright immunity based on level. This could function similar to Sneak attacks vs uncanny Dodge; you would have to be 4 levels higher than your victims uncanny Dodge level to land a successful sneak attack.

3) Finally, if this is actually based on Bleach staying in this kind of field should be DRAINING. I would handle it as 1-10 points of non-lethal damage just from being exposed to this aura. This would of course to be relative to the subjects (like a level 1 commoner should pass out just from exposure within a few rounds)

[Draz74]

OK, while the whole "weight" part of the homebrew race doesn't make much sense as a source of the attack ... weight is a force, and therefore the same units as forces applied in other situations. So I think it makes sense to assume that 10 tons is the force applied outwards, regardless of how that mechanic works.

And I think it sounds like the intended area to be dividing by is the surface area of the 10-ft burst. I.e., 1256.6 square feet.

10 tons spread out over the surface of a 10-ft radius sphere comes out to 0.11 pounds per square inch. Not enough to do much damage.

Of course, the pressure would only be that low on the outer edges of the 10-ft burst. The closer to the source you get, the more the pressure would be at that point.

Halfway out (the average in some sense), the pressure would be ... quadrupled. 0.44 pounds per square inch. Still not exactly fearsome.

[forsaken1111]

If this is indeed inspired by bleach, then the spiritual pressure mechanic applies a downwards force, so as suggested just apply that much 'weight' using the encumbrance rules. This generally means that most characters simply won't be able to move.

If you (or your DM) wants this effect to be lethal, well applying 20 tons of force to anyone will probably kill them regardless unless they can resist using the same spiritual pressure mechanic.

It really is a poorly designed mechanic though as written.

[Shining Wrath]

ok so maybe this will help you answer my question better.

"Certain creatures emit a field of Spiritual Pressure that affect the mind and body..... the effect Spiritual weight has on the body shows that it emits what feels like actual pressure on the subjects. This pressure is greater depending on the creatures Spiritual Rank....works in an aura out to 10 ft. As a standard action (and as part of intimidate) you can surge your aura. While intimidating, there is an actual weight on the enemy...."
ok so my rank and level cause the pressure to be 19,800 lbs

You put 10 tons of weight on top of everything within 10 feet? That's a 5 x 5 block of 5' x 5' cubes, not counting the middle one. So 600 square feet, with 19,800 pounds distributed atop it, is 33 pounds per square foot, or roughly twice the atmosphere.

What is the duration?