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In an answer to Can an Immovable Rod be carried in a Bag of Holding?, you could place an Immovable rod half-in and half outside a bag of holding, and turn it on.

It would be "immovable" in the prime plane, as well as "immovable" in the limited dimension of the bag of holding.

Would this lock the bag of holding into space, say against gravity, or DC 30 strength checks? Since you can't pull the dimension outside of the bag, and that dimension is locked to the rod.

You could climb up a ladder, hold the open bag up, rod half-in, and press the button.... Then lower a 20 1 ton block with a cylindrical hole half the size of the rod on the bottom face, on top of your combination... ;)

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I believe that while the bag and rod would be locked in place, an Immovable Rod halfway into a Bag of Holding will still deactivate or be moved with enough weight or force. That includes any weight in excess of 8,000 lbs. (4 tons) or a DC 30 Strength check. Note that the effects of extreme weight and extreme strength on an Immovable Rod are different.

The text of Immovable Rod is:

This flat iron rod has a button on one end. You can use an action to press the button, which causes the rod to become magically fixed in place. Until you or another creature uses an action to push the button again, the rod doesn't move, even if it is defying gravity. The rod can hold up to 8,000 pounds of weight. More weight causes the rod to deactivate and fall. A creature can use an action to make a DC30 Strength check, moving the fixed rod up to 10 feet on a success.

If more than 8,000 lbs is placed on the Immovable Rod, even if it's placed halfway in a Bag of Holding, it deactivates and the rod and bag fall. A strength check could have multiple results. A creature can pull the rod from the bag (causing the bag to fall off), push it further into the bag (leaving it in the bag's pocket dimension, meaning the bag will fall), or push the rod and the bag 10 feet (the rod stays halfway in the bag). Also consider that weight put on the button could cause it to shut off immediately, even if it's less than 8,000 lbs.

Up to that point, however, I would rule that any force placed on the rod is no different with or without the Bag of Holding. Even placing a ton of weight (2,000 lbs) on the rod shouldn't puncture or break the bag, as the rod is fixed in space and supports the weight entirely. However, I wouldn't say there's any benefit in terms of stability gained by attaching a Bag of Holding to one end, and neither does the linked answer. It simply says that attempting to move an active Immovable Rod into a dimensional space in a Bag of Holding would require a strength check to do, as it's considered to be moving the rod.

Keep in mind that the linked answer is not written rule, merely an interpretation of the effects of an Immovable Rod, the pocket dimensional space of a Bag of Holding, and the nature of physics in the D&D system. It does not override the rules of an Immovable Rod, unless the DM decrees it so.

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    \$\begingroup\$ Except, with the button inside the bag (not being pushed on by the block) it is inaccessible without cutting the bag open. \$\endgroup\$ – user18037 Mar 11 '15 at 14:51
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    \$\begingroup\$ @user18037 Ok, but the rod is still just a rod. Being inside a bag doesn't grant it any fantastic powers beyond those it already had. \$\endgroup\$ – David Reeve Mar 11 '15 at 15:10
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    \$\begingroup\$ Yes. In truth, the bag does not seem to add anything to this scheme that the rod doesn't already do. \$\endgroup\$ – SevenSidedDie Mar 11 '15 at 15:39
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Yes, the bag will be fixed in space. However, the system of the bag and the immovable rod will not necessarily hold against a 20 ton block.

Note that the answer you linked is for the 3.5e. In the 5th edition description bag of holding no longer says that it "opens into a nondimensional space", it only says

This bag has an interior space considerably larger than its outside dimensions

However, description of Heward's handy haversack says

Placing the haversack inside an extradimensional space created by a bag of holding...

Meaning that 5th edition bag of holding works on the same principle as the 3.5e. Descriptions of Immovable Rod are basically the same for two editions (I consider this description for 3.5e). Which means that the logic of the answer for the question you linked holds for the 5th edition as well. Bag of holding with an activated immovable rod half-inside of it is fixed in the space as well.

As for the situation you described in the end, it depends on your opinion of how physics and magic work together. I would rule that the bag receives half of the rod's load (see the reasoning below), meaning that if you load the rod with anything heavier than 1000 lbs (500×2) the bag will burst.


Why does the bag receive half of the rod's load?

The force applied to the rod has to be compensated by something. Since the rod defies everything and can be probably used on any plane it has to be the fabric of the dimension that takes the load, spreading it around in the same way as when you poke yourself with a finger and all the skin around stretches.

Thus, the bag's extradimensional space has to receive the load proportional to the portion of the rod it has inside. The load spreads around and reaches the walls, and the bag feels the load the same way as it normally would.

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  • \$\begingroup\$ But a bag doesn't feel the force of the weight of any object? \$\endgroup\$ – user18037 Mar 11 '15 at 14:53
  • \$\begingroup\$ @user18037 I'm not sure I'm following you, I've explained in my answer why in my opinion the bag feels the weigh of the cement block \$\endgroup\$ – black_fm Mar 11 '15 at 15:07
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    \$\begingroup\$ @user18037 A bag can have force exerted directly on it by a knife, as evidenced by there being rules for what happens if one is pierced. Also, as it's possible to retrieve an item from the bottom of a nearly-empty bag without climbing inside, we can assume that for some reason it is always possible to reach the far side of a bag from the entrance regardless of the length of the object doing the reaching. As such, I'd be very surprised if a stone block pushed partially into the bag wasn't pushing against the far side - and thus straining it - already. (Just a tangent, don't mind me.) \$\endgroup\$ – GMJoe Mar 12 '15 at 2:45
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I think this is being over-thought, but unrealistically. For instance, the rod is stuck in the frame of space, correct? To which reference point?

I think the game designers meant in Reference to the ground and not actual dimensional space. Why? Because if it was in re reference to the activator, it would move along with that said activator staying in exactly the position whether walking jumping up and down or while spinning.

How about relative to the moon? It would be ripped out of your hand and be moving constantly west at the speed of 1 arc second per second approximately or 1 mile a minute at the earths equator.

How about relative to the sun? Well that would depend on the time of day. At noon it would fly west into orbit around the sun at several thousand miles a hour as the bar took 24 days to follow earths orbit at the speed of the Suns rotation. At midnight it would go east, but that's the same direction for the sun. At sunset the bar would fly straight up. At sunrise the bar would go straight down and at that speed it, forget magic, it's inertia would cause it to make a crater the size of a small city.

How about in reference to the galactic core? Shoot, if it hit the ground at those speeds the little bar might cause a disruption of the biosphere causing mass extinction.

What's all this mean? It means it's up to the DM. I think if you put a fixed bar inside a bag of holding that the bag would get stuck until you pushed the button again or you slipped the bag off of it again because the bar is fixed in space relative to the ground

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  • \$\begingroup\$ This entire basis for this answer presumes basic physics that might not be applicable. A different plane of existence may in fact have absolute spacial dimensions. Relativity need not apply. \$\endgroup\$ – InternetHobo Aug 3 '17 at 22:04

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