D&D 5E I'm the DM and a player is trying to abuse the Immovable Rod. Advice?

[AaronOfBarbaria]

It's not the rules, it's physics.

I know, that's what I said.

 

[Yunru]

Besides, weight is relative. Just build it high enough and 8001 pounds becomes 7999 pounds.

 

[merwins]

With a little tinkering, a clever character could probably rig up a system to attach the rods to boots and lock or unlock them with foot movements. Then you're just walking on air.

The universe demands it: https://youtu.be/B4JCehDOy54?t=30s

 

[Sunseeker]

The problem with the Immovable Rod is that it even has a "weight limit". It shouldn't. It should have had a mass limit based on D&D size categories with a variable DC to dislodge it based on the size of the creature making the check. So a medium Immovable Rod would be "immovable" by a medium creature except by a DC 30 Str check, by a Large creature, DC 25, Huge, DC 20, Gargantuan, DC 15. A medium Immovable Rod could carry say, a large load before breaking (10x10x10). And then we wouldn't have to worry about if it is a large load of Lead or a large load of popcorn. Then as Borg Einstein would say: physics is irrelevant.

[MENTION=6701872]AaronOfBarbaria[/MENTION] is right, D&D and physics do not mesh well. The problem is that D&D likes to tiptoe into the waters of science because a lot of us are science-based nerds. They really shouldn't. If we want to apply science to things, that should be our decision. As brought up in the "how many dragons does it take to lift a dragon?" D&D has a horrible weight/carrying capacity calculation and an equally horrible size/mass calculation. D&D would have been much better off calculating carrying capacity in a number of "slots" and then assigning each item a number of slots it fills.

D&D should really attempt to be completely abstract, or completely concrete with its mathematics and measurements. Being somewhere in the middle just makes things confusing and weird.

 

[ThePolarBear]

If you throw something it doesn't go on forever.

Unless it's a Immovable Rod and somehow you activate it in midair. It doesn't exactly GO anywhere... but it sure as hell it does not drop!

If nothingelse, wizards are the scientists of the DND world, as they understand the lawsof physics better than anyone, because you need to understand the laws in orderto understand how to break them. Or at least, those wizards who invented spells understand physics. Everyone else is just copying.

Tell that to the barbarian that just launched himself from way too high in the sky and landed alive. And can do that consistently. I guess he is a very close second to the throne of physics breaker.

When being hit by lightning is 2d10 damage, a crashing flying fortress is 18d10, and 24d10 is the crushing damage of the jaw of a moon sized monster i would say that's not that scandalous that immovable rods actually share a limit. That said, i'm more concerned about finding a big enough amount of those rods and planning construction of said building than anything. A little error and someone has to roll 18d10.

 

[TheCosmicKid]

The problem with the Immovable Rod is that it even has a "weight limit". It shouldn't. It should have had a mass limit based on D&D size categories with a variable DC to dislodge it based on the size of the creature making the check. So a medium Immovable Rod would be "immovable" by a medium creature except by a DC 30 Str check, by a Large creature, DC 25, Huge, DC 20, Gargantuan, DC 15. A medium Immovable Rod could carry say, a large load before breaking (10x10x10). And then we wouldn't have to worry about if it is a large load of Lead or a large load of popcorn. Then as Borg Einstein would say: physics is irrelevant.

@AaronOfBarbaria is right, D&D and physics do not mesh well. The problem is that D&D likes to tiptoe into the waters of science because a lot of us are science-based nerds. They really shouldn't. If we want to apply science to things, that should be our decision. As brought up in the "how many dragons does it take to lift a dragon?" D&D has a horrible weight/carrying capacity calculation and an equally horrible size/mass calculation. D&D would have been much better off calculating carrying capacity in a number of "slots" and then assigning each item a number of slots it fills.

D&D should really attempt to be completely abstract, or completely concrete with its mathematics and measurements. Being somewhere in the middle just makes things confusing and weird.

What? As long as you're not changing gravity fields, mass is a single-variable function of weight. It is not a single-variable function of volume; you need density in there too. A 10x10x10 load of lead is much more massive than a 10x10x10 load of popcorn. So if you want the immovable rod to care about mass, the current mechanic of a weight limit is the correct approximation.

Furthermore, I'd argue that actual weight, and not just weight as a proxy for mass, should be the rod's limiter. Weight is the amount of downward force that the load is applying to the rod. If you want a mass limit (or worse yet a volume limit), what you're saying is that exerting force on the rod isn't what moves the rod. Which is especially weird since you talk about moving the rod with Str checks.

 

[seebs]

It makes a fair bit of sense for it to care about weight, since that's a first approximation of force. How do you move it? By applying enough force to move it, which requires either (1) a DC 30 strength check, or (2) 8,000 pounds of force. Which we handwave and just call "an 8,000 pound object". Presumably, if you wanted to be picky, a smaller object moving fast enough could also move it.

 

[SkidAce]

It makes a fair bit of sense for it to care about weight, since that's a first approximation of force. How do you move it? By applying enough force to move it, which requires either (1) a DC 30 strength check, or (2) 8,000 pounds of force. Which we handwave and just call "an 8,000 pound object". Presumably, if you wanted to be picky, a smaller object moving fast enough could also move it.

Hmmm....so an object moving twice as fast as a standing still "8,000 pound object" would only have to weigh 4,000 pounds. And an object moving twice as fast as that, 2,000, 8 = 1,000, 16 = 500, 32 = 250.

So a 250 pound barbarian could, if moving fast enough....move the immovable rod. Of course it would be a matter of where he gripped it, i.e. by the husk.

 

[Ovinomancer]

Hmmm....so an object moving twice as fast as a standing still "8,000 pound object" would only have to weigh 4,000 pounds. And an object moving twice as fast as that, 2,000, 8 = 1,000, 16 = 500, 32 = 250.

So a 250 pound barbarian could, if moving fast enough....move the immovable rod. Of course it would be a matter of where he gripped it, i.e. by the husk.

Well, no. Force is mass x acceleration. Mass x speed is momentum. Impact force is pretty complicated, especially involving elastic collisions, but, generally, you increase impact force by a factor of 4 per doubling of speed.

And it turns out it takes very little to create 8000lbs of impact force. A grown man (220 lbs, its an easy conversion to metric) jumping onto the rod from 5' up would easily do it. And that's allowing for an elastic collision where you give by a few inches on impact (the rod, of course, wouldn't move, until it did).

 

[Maxperson]

Hmmm....so an object moving twice as fast as a standing still "8,000 pound object" would only have to weigh 4,000 pounds. And an object moving twice as fast as that, 2,000, 8 = 1,000, 16 = 500, 32 = 250.

So a 250 pound barbarian could, if moving fast enough....move the immovable rod. Of course it would be a matter of where he gripped it, i.e. by the husk.

He wouldn't have to grip it. At that point it would be embedded somewhere within his body

Edit: Hmm. Twice as fast as not moving is how fast exactly? Isn't 2 x 0 still 0? Keep multiplying until you have 32 x 0 = 0.