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Old 01-31-2017, 12:32 PM   #1
Varyon
 
Join Date: Jun 2013
Default [RPM] Potential Energy

... or, how to make falling boulders and boxes of explosives in RPM.

This thread is inspired by this ritual and the problem it raises. I think I actually have a relatively simple solution.

See, the issue isn't so much creating a big boulder that can fall on and smash people - it's creating one up in the sky above the character. After all, if someone were to create a boulder right beside them, then push it off a cliff, that doesn't seem an illegitimate option (it's just like being able to create a club without needing to pay for the damage your ogre friend will do with it). Essentially, in addition to just creating a big chunk of rock, you are also creating it with a massive amount of potential energy, calling for Create Energy. Whether this is Lesser or Greater is up to the GM - you might want to follow the damage guidelines from Destroy Matter.

At first, my idea was to add a surcharge to the ritual to account for such energy, but it occurred to me that the Create Advantage actually gives a more-or-less balanced matter-energy equivalence*, which works out to every 100 kJ of energy being worth 1 lb of matter. This should also be doable for explosives and batteries/power cells. Call it Potential Energy for objects created at a great height, Stored Energy for explosives and batteries/power cells.

After doing some unit conversions and simplifying, I've got the equations needed. For adding potential energy (such as creating a boulder 50 yards in the sky, as in the example ritual), use w*h*g/4000, where w is weight in lb, h is height in yards, and g is gravity in G's (1 on Earth), to determine how many lb-equivalents of energy you need to add. For explosives, this is instead 20*w*REF (every pound of TNT has around 2000 kJ in it). In either case, you must pay for both the weight of matter you create and the weight-equivalent of energy you add to it.

So, for that Bridge Breaker Charm, you're looking probably looking at Greater Create Energy (6) + Lesser Create Matter (6) + Lesser Control Magic (5) + Subject Weight, 50 tons (8) + Potential Energy, 1250 lb (5) + Range, 50 yards (8) + Duration, 10 minutes (1)**, for a total of 117 energy (39x3), which seems more appropriate.

For a Conjure C4 ritual that makes a 8 of the typical 1.25 lb blocks of C4 that lasts for up to a day, each 1.25 lb block of C4 contains energy equivalent to 35 lb of Subject Weight, so you're looking at Greater Create Energy (6) + Lesser Create Matter (6) + Subject Weight, 10 lb (0) + Stored Energy, 280 lb (3) + Duration, 1 day (7), for a total of 66 energy (22x3). You'd later detonate them either with normal blasting caps or a Lesser Create Energy ritual.

Optionally, a character can use Path of Matter in place of Path of Energy here (to make a character who can create boulders up in the sky but not fireballs). This is probably a trait worth [5] or so to do so for Potential Energy, but I generally wouldn't make it available for Stored Energy (if it is, maybe another [5] there). Optionally, only allow such characters to do this with rituals for which they either have a Grimoire or Ritual Mastery. Note the ritual that doesn't use Path of Energy is distinct from the one that does.

If you'd prefer, multiply the above equations by 100 (the first becomes 25* rather than /4) to get Potential/Stored Energy in kJ, and multiply the weight column of the Spell Modifiers Table by 100 to change from lb to kJ. Of course, that can result in some pretty big numbers to look at, so you might instead want to divide by 10 in each case to turn things into MJ. The table would change to this:
Code:
Poten/Stored	Added Energy
1 kJ		+0
3 kJ		+1
10 kJ		+2
30 kJ		+3
100 kJ		+4
300 kJ		+5
1 MJ		+6
3 MJ		+7
10 MJ		+8
…		…
(x1000)		(+6)

*E=mc^2 doesn't work here, because it means the 10 lb object you can make without adding any energy is worth something like 80 PJ, if I've done my math right. That's a bit over the output of the Tunguska event.

**Allowing "Momentary" to last long enough for the boulder to hit the ground doesn't seem like a stretch to me, but would only reduce the cost of the spell to 114 energy (38x3).

Last edited by Varyon; 03-25-2021 at 08:09 AM. Reason: correcting J/kJ SNAFU
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Old 01-31-2017, 12:49 PM   #2
Anthony
 
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Default Re: [RPM] Potential Energy

The fundamental problem is that damage and weight are on completely different scales. Plausibly speaking, 'transform' and 'destroy' should be the same magnitude of effect, which means if we leave the weight table alone, we should actually have a damage table sort of like this
Code:
Energy  Weight      Damage
-2      1 lb        1d
-1      3 lbs       1d+2
0       10 lbs.     2d
+1`     30 lbs.     3d
+2      100 lbs.    4d+2
+3      300 lbs.    7d
+4      1,000 lbs.  10d
+5      3,000 lbs.  15d
+6      5 tons      20d
+7      15 tons     30d
+8      50 tons     45d
+9      150 tons    70d
+10     500 tons    100d
Separately from that, your 100 kJ figure is seriously high. My numbers mean that a 1 lb unliving object (4 hp) needs to be moving at 25 yards per second for the correct damage. That's an energy of 118J (not kJ).
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Old 01-31-2017, 01:15 PM   #3
Varyon
 
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Default Re: [RPM] Potential Energy

Quote:
Originally Posted by Anthony View Post
The fundamental problem is that damage and weight are on completely different scales.
My system is scaling things based simply on energy, with no direct consideration for damage. The "1 lb = 100 kJ" figure is based off of Create, where matter is created as 10*(level squared) lb, while energy is 1000*(level squared) kJ.

I'm curious, however, as to how you came to your table. At first it looks like you're assuming an REF .0028 or so explosive for the 10 lb -> 2d figure (consistent with 0 energy for a 2d external explosive), but in that case 1,000 lb of it would do 20d damage, not 10d.
(EDIT: Upon a second review, it looks like you're more-or-less scaling things as +1 SSR to damage per +3 SSR to weight, which would be consistent with scaling explosive damage to the cube root of weight instead of the square root. Is that the case here?)

Quote:
Originally Posted by Anthony View Post
Separately from that, your 100 kJ figure is seriously high. My numbers mean that a 1 lb unliving object (4 hp) needs to be moving at 25 yards per second for the correct damage. That's an energy of 118J (not kJ).
Crap, for some reason I was thinking kg*m/s2 was kJ, not J. I'll update my post shortly.
(EDIT: Updated)

Last edited by Varyon; 01-31-2017 at 01:32 PM.
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Old 01-31-2017, 02:41 PM   #4
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Default Re: [RPM] Potential Energy

Quote:
Originally Posted by Varyon View Post
I'm curious, however, as to how you came to your table.
I started at a base of 'a damage effect should break an unliving object of equal mass' and then rebased it slightly to 1 lb = 1d. Thus, a 1,000 lb unliving object (40 hp) corresponds to a 10d attack (35 damage).
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Old 01-31-2017, 03:40 PM   #5
Varyon
 
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Default Re: [RPM] Potential Energy

Quote:
Originally Posted by Anthony View Post
I started at a base of 'a damage effect should break an unliving object of equal mass' and then rebased it slightly to 1 lb = 1d. Thus, a 1,000 lb unliving object (40 hp) corresponds to a 10d attack (35 damage).
Ah, so I was correct about you scaling by cube root, but was wrong for why you did so.

I'll give it some thought. It would certainly make things more concise than the current methodology I've suggested.
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Old 01-31-2017, 04:39 PM   #6
AnkhLord
 
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Default Re: [RPM] Potential Energy

I am very pleased to have spurred such an interesting debate.

I would imagine that making Gunpowder is not possible with lesser as it is an EXACT chemical mixture. Even if we give it that.
Using Greater Create Matter, three times with a duration of 1 day(39 energy each). Will create the ingredients of Blackpowder.

Now to my original intent.

Based on your critique (MUCH appreciated). Here is the renewed effort. I even went so far as to compute the Size of the beast.

Quote:
Bridge Breaker MKIV
Spell Effects: Lesser Create Matter.
Inherent Modifiers: Area Of Effect, The Cube is roughly 110^3 yards + Subject Weight, 984,150 Tons + Duration, < 10 min.age.
Greater Effects: 0 (1).

The spell has a delay of 30 seconds after breaking. Creates a single solid Cube of Stone, centred on the origin. After breaking the charm it is highly advisable to vacate the area.

This Casting: Lesser Create Matter (6) + Lesser Control Magic (5) + Area Of Effect, 150 yards (22) + Subject Weight, 984,150 tons (17) + Duration, 10 minutes (1). 51 energy (511).
Roughly, (Fast math) 81 tonnes Ft^2. and it stayed on the Ground.
EDIT: The reason to not decrease the Duration is the "secondary effects" of the such a large and heavy object interacting with the world.

Even if I choose not to use such a High weight. Controlling the shape to have a narrow base and wide top would still have the desired effect. Moreover making a multi-ton cylinder would be able to accomplish the goal also.

All this is fun. But the real truth is that a Transform matter at the base of a bridge would be all it would take to wipe it out. Which leads me to believe a clever Ritualist would never have to use more than 50 EP to cause utter destruction.

Ok. So update: The 3 rules Ask if it possible for A person could do it by themselves if it takes a long time and equipment, possible. If any are yes then it might be Greater, if 2 are yes. it is Most Likely Greater.
3 is clearly a greater or more.

Last edited by AnkhLord; 02-01-2017 at 01:35 PM. Reason: Idea after posting. Found other rules.
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Old 01-31-2017, 10:36 PM   #7
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Default Re: [RPM] Potential Energy

I would generally avoid any calculations of energy or energy-pressure generated by the falling object, just as I would avoid checking the shear modulus for the wooden beams or measuring the length of time of contact between the boulder.

The number one rule of RPM is that it is a Rule Zero system. If the intent of casting the spell is to inflict a bunch of damage, the vehicle by which said damage is delivered is irrelevant, especially if that vehicle will blink out of existence right after dealing that damage. As such, this is simply adding the Damage modifier to the spell with sufficient quantity and modifiers to represent a massive falling boulder. That it creates a massive falling boulder simply gives the option to cast this as a Create Matter effect instead of a Destroy Matter effect. I'd allow either for this sort of thing, personally, but others might be more stringent.

If the boulder is to stick around afterward for a while, I'd treat this as two effects: Create Matter (to make a semi-permanent boulder) and Destroy Matter (to trash the bridge/squash the troll/etc.).

Personally, I'd be curious to hear how PK would adjudicate this situation.
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Old 02-01-2017, 11:20 AM   #8
Varyon
 
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Default Re: [RPM] Potential Energy

Quote:
Originally Posted by AnkhLord View Post
I would imagine that making Gunpowder is not possible with lesser as it is an EXACT chemical mixture. Even if we give it that.
Using Greater Create Matter, three times with a duration of 1 day(39 energy each). Will create the ingredients of Blackpowder.
Black powder isn't as complex as a crossbow, which I think is the simplest thing that calls for Greater. It would require a skill roll, just as making it from raw materials does - Explosives (Fireworks) or Chemistry at +4, or Explosives (Demolition) at full skill. Failing that, saltpeter, charcoal, and sulfur are certainly simple enough for Lesser Create, so three uses of that could make the raw materials, then you use normal skill and tools to make the explosive.

Quote:
Originally Posted by AnkhLord View Post
Based on your critique (MUCH appreciated). Here is the renewed effort. I even went so far as to compute the Size of the beast.
I don't think you need Area of Effect here - that's to affect multiple targets, not something you need to throw on to account for the large surface area of the thing you created. And, yeah, with that much weight you probably break through the bridge without needing to account for anything else. With Lesser Create Matter, you boulder is probably more an amorphous lump that approximates a cube (or cylinder, or whatever shape you're shooting for), but that should be fine, as you're going for sheer weight rather than aesthetics.

Quote:
Originally Posted by Humabout View Post
The number one rule of RPM is that it is a Rule Zero system. If the intent of casting the spell is to inflict a bunch of damage, the vehicle by which said damage is delivered is irrelevant, especially if that vehicle will blink out of existence right after dealing that damage. As such, this is simply adding the Damage modifier to the spell with sufficient quantity and modifiers to represent a massive falling boulder. That it creates a massive falling boulder simply gives the option to cast this as a Create Matter effect instead of a Destroy Matter effect. I'd allow either for this sort of thing, personally, but others might be more stringent.
As a GM, I'm alright with not using the normal Damage modifier for something like this. I wouldn't have an issue with a ritualist at the top of a cliff using a non-damaging ritual spell to make a boulder and then shove it off to smash something below. With that in mind, there doesn't feel like there should be anything stopping a flying mage from using the same ritual to make an adjacent boulder, which would similarly fall and crush whatever was beneath. The issue is that doing either of those requires a difficult setup and precise aiming, while Ankhlord's ritual is basically just "Cast, Run, Smash" (or worse, "throw at the target, enjoy the view" if it's an ammunition Charm), because it adds in a vertical component to the ritual. As I'm alright with making an object at the same elevation as the character with a normal Create Matter effect, but higher elevation means higher potential energy, I opted for a surcharge for said potential energy.

Of course, if someone wants to use the normal Damage modifier for a similar ritual, like a rain of stones, I'm fine with that.
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Old 02-01-2017, 11:50 AM   #9
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Default Re: [RPM] Potential Energy

If you made the rock at your altitude and just dropped it, that would probably require a Dropping roll to hit.
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Old 02-01-2017, 02:01 PM   #10
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Default Re: [RPM] Potential Energy

Quote:
Originally Posted by Humabout View Post
The number one rule of RPM is that it is a Rule Zero system. If the intent of casting the spell is to inflict a bunch of damage, the vehicle by which said damage is delivered is irrelevant, especially if that vehicle will blink out of existence right after dealing that damage. As such, this is simply adding the Damage modifier to the spell with sufficient quantity and modifiers to represent a massive falling boulder. That it creates a massive falling boulder simply gives the option to cast this as a Create Matter effect instead of a Destroy Matter effect. I'd allow either for this sort of thing, personally, but others might be more stringent.
Yep. This is overthinking the subject. Just add the damage modifier.
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