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Old 02-13-2020, 07:51 PM   #1
OddGamer
 
Join Date: Jul 2005
Location: Ontario, Canada
Default Melting ice fast

I'm trying to model a cartoon in GURPS (I know, not a good idea), and I came across an interesting issue that I don't know if there are rules for it or where they are.
In the cartoon involved, a very large hunk of ice was falling and the 'hero' involved blasted said hunk of ice with a fire attack, melting the whole thing. I suspect that it's some insane level of damage and I'll be dialing it back for actual combat (calling that a 'special effect' sort of idea). So is there somewhere that mentions how much burning type damage is needed to melt different amounts of ice, whether linear or some form of curve?
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Old 02-13-2020, 08:39 PM   #2
Anthony
 
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Default Re: Melting ice fast

It takes around ten times as much energy to melt a human-sized chunk of ice as it takes to kill a human by raising their body temperature outside of the survivable range. However, in mechanical terms I'd probably just figure reducing a chunk of ice to -10xHP completely melts it (far less to make it shatter).
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Old 02-13-2020, 09:01 PM   #3
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Default Re: Melting ice fast

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Originally Posted by Anthony View Post
It takes around ten times as much energy to melt a human-sized chunk of ice as it takes to kill a human by raising their body temperature outside of the survivable range. However, in mechanical terms I'd probably just figure reducing a chunk of ice to -10xHP completely melts it (far less to make it shatter).
Given the density of ice isn't that far off from the density of a person, and that ice is homogenous, you're probably looking at damage in the vicinity of 400 (~115d) burn to melt a human-sized chunk of ice.

Another option would be to use the beam weapons from Spaceships. Every kg of ice requires around 333.55 kJ to melt it once it reaches 0 C. Our weapon from above would be around 100 MJ (which is actually 100d burn), which would melt right around 300 kg of ice. Melting a chunk of ice of roughly human weight (62 kg) would require around 20 MJ, roughly 50d or so. That's 175 damage to melt 137 lb. Because the damage of beam weapons vs energy and quantity of HP vs mass actually both scale by cube root, that ratio should be fairly constant - call it 1.25 burn damage for every pound of ice that needs to get melted. Note you'll typically need to heat up the ice to get it to 0 C before you melt it, but IIRC the energy to shift it up to melting temperature is very low compared to what's needed to actually melt it.
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Old 02-13-2020, 09:28 PM   #4
Dalillama
 
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Default Re: Melting ice fast

Buy a Burning IA with enough damage to be impressive, then buy Create (Ice) with Destruction Only as an alternate ability.
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Old 02-13-2020, 11:06 PM   #5
Fred Brackin
 
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Default Re: Melting ice fast

Quote:
Originally Posted by Anthony View Post
, in mechanical terms I'd probably just figure reducing a chunk of ice to -10xHP completely melts it (far less to make it shatter).
If you're going to have enough energy to melt the whole mass of ice in less than one second you're probably going to push the first bit of ice through 2 phase changes from ice to liquid water to steam and that's going to eb an explosion.

The OP asked if there were rules and the rules in question are the Object Hit Pts Table on B. 558 modifed by the rules fro Fragile(Brittle) from p.136 and quite possibly Vulnerability p.161.

First you figure out how heavy your chunk of ice is. It's a given that water is 1 metric ton per cubic meter and that ice is 92& as dense as water or (switching from kg to the lbs the table is in) 2024 lbs per cubic meter.

Unless we actually are dealing with Ice Cubes Of Unusual Size (ICOUS) you're estimations of size are going to be rough anyway so you might as well pick an even number for weight.

The table on p.558 (or use of the formula under it) will then give you HP. Fragile(Brittle) cmes in as soon as a HT Roll to avoid Death is failed which will cause the cube to immediately go to -HPx10.

Play with the size of the fire attack, the size of the the ice chunk and whether or how much Vulnerability to Fire to give it to get the result that satisfies you. Maybe easy to Kill too.
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Old 02-13-2020, 11:23 PM   #6
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Default Re: Melting ice fast

This seems like Power Parry from Supers. IIRC, 1d of attack parries 1d of attack. So, 1d of burning will parry 1d of crushing (from the falling ice). Physics can go lump itself. If the GM wants to describe that as the ice melting or even sublimating, then... cool!

Cartoons are at least supers-adjacent, so I'd be happy porting those rules if the feel is right.
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Old 02-14-2020, 09:39 AM   #7
OddGamer
 
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Default Re: Melting ice fast

Some good thoughts here, and I can't believe I managed to miss the box. Kinda ticked at myself. I'm probably just as much missing the (blatantly obvious) bit where this next question comes in, but... well. Are there rules for area affects or (more specifically) cones striking large object? (The attack in question is a cone attack, specifically a breath weapon.) After all, if your attack does 10 damage to each hex it hits, then if you're talking about a multi-hex item (yes, the thing was that big, it's a cartoon), it should take the damage for each hex actually hit, shouldn't it? That would vastly reduce the dice of damage needed.

On a side note, since the weight of the object involved is in the calculations, are strengths involved in multiple people trying to lift/slow the descent of something simply added together? They were flying (wings, though unrealistically small ones), if that matters. I'm somewhat guessing on the numbers involved in trying to stop this thing from hitting, but it should give me a better idea of the weight than trying to work out the volume of an object I can only see in two dimensions.
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Old 02-14-2020, 10:12 AM   #8
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Default Re: Melting ice fast

Quote:
Originally Posted by OddGamer View Post
On a side note, since the weight of the object involved is in the calculations, are strengths involved in multiple people trying to lift/slow the descent of something simply added together? They were flying (wings, though unrealistically small ones), if that matters. I'm somewhat guessing on the numbers involved in trying to stop this thing from hitting, but it should give me a better idea of the weight than trying to work out the volume of an object I can only see in two dimensions.
Add up the Basic Lift and match it up to the closest ST score that matches the sum. Just adding up ST scores will produce extremely wonky results.
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Old 02-14-2020, 07:09 PM   #9
Varyon
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Default Re: Melting ice fast

Quote:
Originally Posted by OddGamer View Post
Some good thoughts here, and I can't believe I managed to miss the box. Kinda ticked at myself. I'm probably just as much missing the (blatantly obvious) bit where this next question comes in, but... well. Are there rules for area affects or (more specifically) cones striking large object? (The attack in question is a cone attack, specifically a breath weapon.) After all, if your attack does 10 damage to each hex it hits, then if you're talking about a multi-hex item (yes, the thing was that big, it's a cartoon), it should take the damage for each hex actually hit, shouldn't it? That would vastly reduce the dice of damage needed.
Realistically, area effects (such as cones) should do more damage to larger targets than to smaller ones. Roughly speaking, so long as the target is completely within the area of effect, every +1 to SM should be +1 SSR (x1.5, x2, x3, x5, etc) to damage, while every -1 to SM should be -1 SSR (x0.7, x0.5, x0.3, etc) to damage. I think. By GURPS RAW, however, this is not the case, even if the the target covers multiple hexes.

Quote:
Originally Posted by OddGamer View Post
On a side note, since the weight of the object involved is in the calculations, are strengths involved in multiple people trying to lift/slow the descent of something simply added together? They were flying (wings, though unrealistically small ones), if that matters. I'm somewhat guessing on the numbers involved in trying to stop this thing from hitting, but it should give me a better idea of the weight than trying to work out the volume of an object I can only see in two dimensions.
As awesomenessofme1 notes, when combining the strength of multiple characters you should combine their Basic Lifts. If you need an ST score, you can back-calculate, but I assume this is a case where you essentially need to know the Basic Lift of the combined force of everyone listed, in which case no conversion is necessary.
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