D&D General Is this a fair trap?

[Ruin Explorer]

With 10' x 10' 10' block of solid granite it would most certainly be completely spilled out of the pit.

Yeah, but not quickly. It would gradually jet out as the block (which would necessarily be somewhat smaller than that) slowly sank. The closer to 10x10x10, the slower it's likely to be, because the amount of goo that can leak out will be limited. It's also possible it just stops at some point, because the block is unstable, and it's goo, not water - so the block may well lean slightly in a direction and then jam.

Also, if it's granite and that big, it's not rope, and you're altering the scenario to make it a magical rope or giant's hair or w/e, which is not the trap as written.

 

[Maxperson]

You haven't addressed the other various failings of the situation, like the fire killing the Yellow Mold, either.

The mold never gets touched. It's on top of the stone block. The rope is very narrow and the fire isn't going to spread out over the top of the block. Further, if you want to spare the few centimeters of mold near the rope entry point, you just put a 6" pipe into the block at the point where the rope comes out and the fire never touches any of the mold.

 

[Maxperson]

The block weighs at most 8000lb, not 50 tons, as I've established. The positioning of the Yellow Mold given the arrangement of ropes described to hold up the block means it is necessarily in direct contact with the "flammable ropes". It's their choice to describe the block being hung the way it was.

Plus the 10x10x10 basis for the size of the falling block is not only not going to work mechanically, but it's simply not textual. It's a number made up by another poster with no basis for doing so.

Size to Weight Calculator (Rectangular Box)

The size to weight calculator (rectangular box) evaluates the weight of a rectangular box.

www.omnicalculator.com

I put in 10x10x10 for dimensions and used granite, which has a density of 165-172 pounds per cubic foot. I used 170 for nice even numbers. That block came out weighing 170,000 pounds or 85 tons.

 

[pemerton]

Did a little rendition how I think it might work…

The original article has a picture/diagram with labelled components. Yours is cooler!

 

[Maxperson]

From the OP:

the rope is in fact supporting a large stone block that sits in the ceiling above the pit (by passing through a hole in the middle of the block, over a hook/pulley that hangs from the true ceiling above the block, and then splits or is knotted into four strands which run to each corner of the block, thereby suspending it).

That means the rope would have to pass through the yellow mold on top of the block, as well as the block itself.

Not with a simple 6" pipe inserted into the top of the block at the point where the rope enters.

 

[Nefermandias]

Yeah, but not quickly. It would gradually jet out as the block (which would necessarily be somewhat smaller than that) slowly sank. The closer to 10x10x10, the slower it's likely to be, because the amount of goo that can leak out will be limited. It's also possible it just stops at some point, because the block is unstable, and it's goo, not water - so the block may well lean slightly in a direction and then jam.

Also, if it's granite and that big, it's not rope, and you're altering the scenario to make it a magical rope or giant's hair or w/e, which is not the trap as written.

Yes, no way the goo is going to be explosively pushed out of the pit. Still, people in the vicinity would still get hit by it. And yes, I thought the super strong, magic rope was a given at this point.

 

[pemerton]

Over a mere ten-foot drop for something that heavy air resistance is going to be negligible.

The YM is on top of the falling rock, right? The burning rope is all beneath the falling rock, right? Therefore, how can the YM catch fire in this scenario without the PCs causing it?

I think we're agreed here. I think @Ruin Explorer's figures for velocity are wrong. And likewise his supposition about the fire on the rope killing the mould.

Note that the trap description in the OP specifically mentions that the pit is a 10' cube. The one-foot lip is a later invention, out of discussion in this thread; and its presence takes away any real hope of the splatter effect working.

There is no mention of any lip in the text. There is a small lip in Roger Musson's picture. Whether it would stop the Cube splatter I don't know - in @Stormonu's diagram it doesn't seem to!

 

[pemerton]

Come to think of it, wouldn’t the fire suffocate inside the hole in the block? That would still cause the block to drop and avoid the risk of the fire touching the mold.

This is what @AbdulAlhazred said upthread.

Wait, what’s the rope secured to on the bottom? Wouldn’t the gelatinous cube burn through it?

It's a metal ring. In the AD&D MM, metal is described as "indigestible" by Gelatinous Cubes. That's why they have treasure floating inside them!

 

[tomBitonti]

So ... unless the GC material is compressible, if the block is nearly as big as the pit and falls face on, the impact is likely to be quite jarring; nearly instantaneous. The GC material towards the center won’t have enough time to flow out of the was of the cube.

it does seem that a narrow band of GC material might be expelled quite explosively by the initial impact. I’m thinking as a fine mist and dispersing in a wide plume.

In term of dimension and the mass of the stone block, keep in mind that the GC scales at the same rate as the cube. What matters is the height of the cube, not so much its width, and probably the relative density of the rock vs the GC material. Although, the GC material might be close to water. Or not, if there is a lot dissolved in it.

TomB

 

[tomBitonti]

So .. at 170 lb / cu ft, a 10 ft column of granite has about 12 psi (pounds per square inch) of pressure. A typical home water pressure is 50 psi, four times that. This pressure forcing GC material up seems to be quite low. Most of the effect would likely be from the initial impact.

in my prior post, I imagined the block hitting face on. The situation seems quite different if the block is rotated 1/8 of a turn (45 degrees).

TomB