Shrink Item

[sikyon]

Hey peeps,

How do you handle physics with shrink item in your games? Say, you toss a shrunk item and it expands in flight. How do you handle conservation of momentum and conservation of energy? Or do you just ignore it?

[Eldmor]

The mound of dead cat-girls and cheese give full cover and concealment to the target.

[Nonah_Me]

Respond to this inqury in character:

Wizard: My magic reshapes reality itself! Physics cannot bind me, fool!

Fighter: I don't care how, as long as I can use the collossal darts.

Barbarian: *scratches head* Yoo must be baddie mage! *smash*

Just ignore those things.

[brian c]

Since it doesn't have to make sense, screw conservation of momentum (etc). Just say the velocity, range and everything are the same, but the thing is huge now.

[goat]

The RAW won't really handle it, which is why the last thread I remember about this went on for quite a few pages. Basically, arguing the physical effects of something that, as its core effect, defies the laws of thermodynamics is just never a good idea.

Just play it the way that makes the most narrative sense. If you need it to expand and travel another 100 feet, let it work. If someone's trying to abuse a giant returning harpoon'o'doom, then it probably shouldn't.

[Kaelik]

Here's what I hate about people bringing up conservation of momentum/energy as regards thrown shunk objects.

An item is on a table. It is not moving at all. It gets bigger. Because the mass increases it now has a greater potential energy. The only counter for this is to teleport downward. Clearly that makes no sense. Obviously ALL exapansions increase energy in the universe. All shrinking decreases energy. So why on Earth are you arguing about conserving it only in the limited context of thrown objects, even though clearly it is impossible to use the spell in a way that maintains conservation of energy.

[Kantolin]

Personally, a rock doing (say) 4d8 damage due to being raised 4 categories from relatively small rock numbers, using a third level spell, and requiring preparation doesn't strike me as all that bad.

Sure, they can put more effort into trying to break it further, but hey. Four size categories up doesn't seem all that horrible compared to, let's say, 1d3 rock damage?

[Chronos]

Physics is the set of rules which governs the way the world works. The set of rules which govern the way the D&D world works are bound up in those books from Wizards of the Coast. Therefore, those rules in the PHB and such are the physics of D&D. D&D physics may often bear a striking resemblance to the physics of our world, but that does not mean that they are identical, and we should not be surprised when they disagree. In fact, they must sometimes disagree, since the physics of D&D allows for the existence of magic, while our own physics does not.

While the rulebooks don't specifically address the question of using Shrink Item on weapons, they do address a number of similar situations, where a weapon changes size in midair. From spells like Enlarge Person and Righteous Might, we see that

Melee and projectile weapons deal more damage. Other magical properties are not affected by this spell. Any enlarged item that leaves your possession (including a projectile or thrown weapon) instantly returns to its normal size. This means that thrown weapons deal their normal damage (projectiles deal damage based on the size of the weapon that fired them).

From this, we can reasonably extrapolate that a medium-sized character throwing a shrunken dart does damage as a colossal-scale dart, but that a medium-sized character loading his crossbow with shrunken bolts only does the damage of a medium-scale crossbow.

[Jack Zander]

But what happens when you Gaseous Form inside someone's lungs and dismiss the spell? The rules for Reduce Person suggest that you break them apart with no damage to yourself, but the Gaseous Form text says nothing about ending the spell when in a confined space.

[Nonah_Me]

Can you be hurt in Gaseous Form? If so, you provoke an AoO when trying to enter an opponent's space (er...lungs).

[JackMage666]

Can you be hurt in Gaseous Form? If so, you provoke an AoO when trying to enter an opponent's space (er...lungs).

But who's going to attack his own lungs, seriously?

[goat]

But who's going to attack his own lungs, seriously?

Someone with AWESOME regeneration.

[Jack Zander]

Yes you can be attacked but you have DR 20/magic.

[Enguhl]

The shrunken (now expanded) item will be reduced to 1/4,000 (or however much you shrunk it) of its original, forward velocity.

[WorthingSon]

But what happens when you Gaseous Form inside someone's lungs and dismiss the spell? The rules for Reduce Person suggest that you break them apart with no damage to yourself, but the Gaseous Form text says nothing about ending the spell when in a confined space.

... must... try...

[Kaelik]

The shrunken (now expanded) item will be reduced to 1/4,000 (or however much you shrunk it) of its original, forward velocity.

No it won't, because you decrease the energy of the universe when you shrunk it. So you increase the energy when you expand it.

[Jack Zander]

... must... try...

Go ahead, pull it on your DM and see what happens. He'll probably be dumbfounded the first time, but DM fiat that it doesn't work after that first piece of cheese was used.

[Nonah_Me]

But who's going to attack his own lungs, seriously?

Tiny, Diminutive, and Fine Creatures
-snip-
Creatures that take up less than 1 square of space typically have a natural reach of 0 feet, meaning they can’t reach into adjacent squares. They must enter an opponent’s square to attack in melee. This provokes an attack of opportunity from the opponent. You can attack into your own square if you need to, so you can attack such creatures normally.
-snip-

Gaseous form isn't a tiny creature, but were I DMing a game where someone tried this I'd use that rule. Therefore, someone with a +1 weapon would be able to attack the gas BEFORE they entered the lungs, thus granting the AoO.
Never said they would actually attack them once inside the lungs. That's pretty funny though.

Player: Uh...I plunge the dagger into my chest.
DM: Wha? Alright, you coup de grace yourself. Roll attack with a -10 penalty for...um...dying?

[Jack Zander]

Player: Uh...I plunge the dagger into my chest.
DM: Wha? Alright, you coup de grace yourself. Roll attack with a -10 penalty for...um...dying?

Hey, if you're going to die anyway it's worth a shot...

[Belteshazzar]

I belive a certain comic book villan would say that being inhaled in gassious form makes you into nothing more than fancy nose candy. I cant remember the particular comic but I remember the image of a rather firery looking being in a suit being inhaled though the nostrals of very pleased looking muclebound brute being used in certain Motivator Posters.

[Enguhl]

No it won't, because you decrease the energy of the universe when you shrunk it. So you increase the energy when you expand it.

Only the potential energy due to gravity, not the kinetic energy involved with its forwards movements.

[Kaelik]

Only the potential energy due to gravity, not the kinetic energy involved with its forwards movements.

Unless you target a moving object for shrinking. Besides, how does, "It only violates the conservation of energy in one way, therefore it should have to follow it in another" make any sense?

Is Shrink Item evocation/transmutation/or conjuration? If so it automatically breaks conservation of energy by definition.

[Enguhl]

Unless you target a moving object for shrinking. Besides, how does, "It only violates the conservation of energy in one way, therefore it should have to follow it in another" make any sense?

Is Shrink Item evocation/transmutation/or conjuration? If so it automatically breaks conservation of energy by definition.

The conservation of energy only applies perfectly. When you are talking about it growing in mid flight, when it gets bigger and its potential gains because it has more mass, therefore more potential energy, thus to conserve the kinetic balance, it slows down.

I think this thread just got killed by physics...

[Lochar]

If not that, then the pile of dead catgirls buried the thread.

[Enguhl]

If not that, then the pile of dead catgirls buried the thread.

Poor cat girls... they shall be missed.
Not by me. But missed none the less.

[Kaelik]

The conservation of energy only applies perfectly. When you are talking about it growing in mid flight, when it gets bigger and its potential gains because it has more mass, therefore more potential energy, thus to conserve the kinetic balance, it slows down.

I think this thread just got killed by physics...

The problem is that a non-moving item growing bigger violates conservation of energy all by itself. A stationary object growing bigger increases it's potential energy. There is no kinetic energy to be reduced. Therefore, the end of the spell dictates the increase of energy in the universe every single time. So why would it reduce the increase in energy when it absolutely cannot remove it?

[Aquillion]

The conservation of energy only applies perfectly. When you are talking about it growing in mid flight, when it gets bigger and its potential gains because it has more mass, therefore more potential energy, thus to conserve the kinetic balance, it slows down.

I think this thread just got killed by physics...

MAGIC.

More seriously, though, we don't know exactly how Shrink Item works or what it does in physics terms, so we can't say anything about how it should behave. Possibly the item's mass is simply 'shunted' elsewhere, temporarily converted into a form of energy that we don't know about, or whatever.

This would explain why the object instantly returns to normal when subjected to a dispel magic (there's no logical reason why it would, is there? Not unless the spell was actively 'hiding' the mass the entire time.) The spell is shifting a portion of the subject's mass along another dimension or whatever, and actively preventing the hidden mass from impacting the real world. The energy to do this is provided by the usual energy source for spells and magic, which varies from setting to setting.

Note that for Shrink Item to work in this way at all, the spell must provide the energy necessary to manipulate the 'hidden' portion of mass in tandum with the unhidden portion. For instance, if you shrink a table and pick it up, the spell will lift the 'hidden' 3999/4000ths of its mass for you.

This means that if you Shrink Item a rock, carry it up a hill, then unshrink it, the actual 'lifting' to bring all that missing mass up the hill was provided by the spell, which was essentially 'lifting' the rock the whole time by suppressing part of its mass and the related effects. Likewise, when you throw a shrunken boulder, the Shrink Item spell provides the necessary energy to get the 'hidden' mass moving along with the object's unhidden portion... and then ends, revealing everything. From our perspective, it appears as though extra mass and kinetic energy have appeared from nowhere, but this is not the case.

[Mordan]

Wizard: umm... I'll use my magic missile spell on him
DM: Okay, as soon as you can explain using physics, chemistry and correct mathematical knowledge, where the fire comes from and why it doesn't dissipate as it hurls from you to the target. And then explain why it should suddenly affect said target.
Wizard: umm... Okay, I'll try cone of c... never mine, what's about..? Screw it, I quit. Next week, someone else gets to DM.

Why is there even a discussion about how it can happen? It's magic. Who cares if the object is instantly made smaller, or if it takes nth of a second to shrink? Who cares how much of weight is being magically supported by the spell? Does it really matter? It's magic!!

[Enguhl]

Why is there even a discussion about how it can happen?

Was bored

[Chronos]

On the Gaseous Form question, there's a monster with a similar ability, the Belker (not to be confused with any psychotic halflings we know).