[RPM] Potential Energy

[Varyon]

... 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:

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).