How does the "Knock" spell physically work? ( Unlimited cheese potential )

[Renduaz]

Particularly the function of making any object with a mundane or magical means which prevent access "unbarred" or "unstuck", while "unlocked" is less interesting since I'm assuming it would just replicate the clicking of the appropriate key or slot or magical password. Actually on second thought, it's also interesting how it does that. But let's start with something else first, for example, consider the classically barred door (http://i.imgur.com/l542U7E.png) as shown on the left of this picture, it's handles barred from the other side with a plank of wood or iron.

Now, a Knock spell is meant to unbar that. How so? You might imagine that the simplest method would be for the bar to slide out of the handle on it's own provided there is enough space. Even something as simple as that, if the DM were to designate it as such, already gives us the very first exploitable property of "Knock", under the premise it will unbar any door which is barred by mundane or magical means, as long as there isn't an Arcane Lock spell. That property is:

- Knock can move anything, as long as it prevents access to an object, in any direction which will enable access once the matter has been moved

But what if as the illustration to the right of the image shows, someone has welded two iron cubes larger than the openings inside the door handles on each side of a metal rod, such that it can't slide off? ( Much like a lifting weight ) Will the DM make "Knock" break the metal rod in the middle or break of the cubes? Will it vanish? Will it become temporarily immaterial? If so, then:

- Knock could break anything, as long as it makes an object barred or stuck and generally prevents access to it

- Knock will make anything disappear, either temporarily or permanently, as long as it bars or generally prevents access to an object

Do you see where we're going with this? Now, when it comes to unlocking locks, does the spell "Knock" replicate, for instance, the sequence produced by a key in a pin-tumbler lock? If so, say I forged a door which can only be opened by lifting a giant pin with a giant key, and I place some kind of really have object on that pin so that it's stuck, would Knock allow me to engineer some kind of unlimited hydraulic lift?

If Knock would move, break or de-materilize anything which bars a door for example, could I create some kind of perpetual Knock engine with the power to move absolutely anything of any weight? Could I carry a portable door like the one in the picture with me, insert a metal rod , place it between walls in a hall and watch as the metal rod burrows a hole in that hole as Knock pushes it away from barring the portable door with infinite strength? Or use it as a battering ram?

If "Knock" breaks instead of moves, Could I break magical artifacts by fitting them into custom-designed door handles, install that door in the house, cast Knock and break the artifact in two? Can I take a hoop of metal, weld off a section, fit it around a column, re-attach the section with Mending, and cast Knock to make it unstuck by breaking the column? Could I use a spell like Teleport to teleport a tiny speck of dust inside a tiny pore in a boulder and break the boulder with Knock since my speck of dust is stuck there and it bars the access? And I haven't even envisioned all the infinite possibilities so far, in fact there are probably engineers here who could think flawless and more useful ideas, depending on how Knock works in campaign. It seems to me though that no matter which way "Knock" unbars or makes something unstuck, it can be exploited as a source of infinite energy and cheese.

[rollingForInit]

The spells says, "A target that is held shut by a mundane lock or that is stuck or barred becomes unlocked, unstuck, or unbarred."

I think it depends entirely on DM adjucation, and I'd do it one of two ways.

1) Knock fails in situations such as yours. The door is no longer "locked" or even merely "barred", it's just welded shut, for all intents and purposes. It cannot be opened by a key, it cannot be opened from the other side without seriously breaking things apart. It's a bit like taking a small iron chest and welding it shut. It wouldn't be locked any longer, it'd just be a hollowed out iron object. Knock would now be insufficient to open it. In regards to your door, I see it as comparable to someone just shoving a big rock up against it. Knock wouldn't fix that, either. And it seems like a much simpler solution than the one in your picture as well.

2) Knock still works, but it does nothing beyond removing whatever is blocking, and unblocks in the most minimal of ways. In your picture, the metal rod might break and fall apart. An artifact wouldn't, because an artifact cannot be destroyed, so then it might just magically fall off, undamaged. How does it pass throught the rocks without breaking them? Magic. The spell isn't going to do anything remarkable enough to create an inifinite Knock engine or a portable battering ram.

And I'd always rule that Knock cannot break a stone containing something. An actual stone that has something inside it is not an object similar to a door, chest, box, padlock, etc. For Knock to work, the target must be held shut by a mundane lock, be stuck or barred. A stone isn't "barred" by simply being a stone.

The main issue with trying to go outside a spell's intended uses in a system like D&D, is that magic is literally magical, subject to cosmic rules, divine decrees and whatever else. It can have very arbitrary limitations.

[Renduaz]

The spells says, "A target that is held shut by a mundane lock or that is stuck or barred becomes unlocked, unstuck, or unbarred."

I think it depends entirely on DM adjucation, and I'd do it one of two ways.

1) Knock fails in situations such as yours. The door is no longer "locked" or even merely "barred", it's just welded shut, for all intents and purposes. It cannot be opened by a key, it cannot be opened from the other side without seriously breaking things apart. It's a bit like taking a small iron chest and welding it shut. It wouldn't be locked any longer, it'd just be a hollowed out iron object. Knock would now be insufficient to open it. In regards to your door, I see it as comparable to someone just shoving a big rock up against it. Knock wouldn't fix that, either. And it seems like a much simpler solution than the one in your picture as well.

2) Knock still works, but it does nothing beyond removing whatever is blocking, and unblocks in the most minimal of ways. In your picture, the metal rod might break and fall apart. An artifact wouldn't, because an artifact cannot be destroyed, so then it might just magically fall off, undamaged. How does it pass throught the rocks without breaking them? Magic. The spell isn't going to do anything remarkable enough to create an inifinite Knock engine or a portable battering ram.

And I'd always rule that Knock cannot break a stone containing something. An actual stone that has something inside it is not an object similar to a door, chest, box, padlock, etc. For Knock to work, the target must be held shut by a mundane lock, be stuck or barred. A stone isn't "barred" by simply being a stone.

The main issue with trying to go outside a spell's intended uses in a system like D&D, is that magic is literally magical, subject to cosmic rules, divine decrees and whatever else. It can have very arbitrary limitations.

I could still see uses for being able to break a metal rod and everything else with Knock. But as I've said, I've been thinking very little about the scenarios, but I do believe regardless of what you decide, Knock could be exploited. If you would consider the door in that example to be "Welded shut", Could you give me something like 2 barring or stucking mechanisms which you'd consider an object to be "barred" or "stuck" by, and how would Knock un-bar, or un-stuck that?

[tieren]

I tend to picture this spell a little more Harry Potter-ish, you tap your wand against the thing and it changes to open.

If its a mundane lock it pops open, not necessarily because the right tumblers were activated in the right sequence, maybe the gears went smooth or wobbly for a minute and nothing was then holding the bolt back.

In your barred door example, maybe the rod with the weights stays perfectly the same but the brackets holding it to the door turn to jello for a moment and the bar slides through and falls away.

Maybe a stuck door actually shrinks 1 inch and is no longer stuck into the surrounding walls, etc...

However you envision it it should be instantaneous and to the extent possible return to normal after the spell ends (other than the thing now being unlocked/unstuck.