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Talakeal
2013-07-04, 06:47 PM
In my games players frequently try and apply real world physics to a magical / sci fi situation to create some sort of an exploit. If I tell them it doesn't work like this, then they pick apart the entire technology and insist that if it doesn't work their way it doesn't work at all. I see a lot of similar arguments on this forum.

The most common offender is force fields of various sorts. Either those created by the D&D Wall of Force spell or a Sci Fi forcefield like what the Enterprise uses to seal breaches or restrain prisoners on Star Trek.

So, I would like to ask a few questions about people's opinions on Force Fields and the physics behind them:

1: Does a force field behave like solid matter or does it behave more like a strong magnetic field that repels all matter?

1a: How much impact does running into a force field generate? Is it any? Does anyone know if you hurl a metal object into a strong enough magnetic field if the metal object will sustain structural damage from the impact or merely decelerate and stop dead?

2: Does a force field have friction?

2a: Is it possible to climb a force field?

2b: If one is stuck on top of a horizontal force field can one push off it to escape or is one trapped?

2c: Can a mobile force field be used to carry objects? Is there a weight limit?

3: Just how strong is a force field?

3a: If hit with a huge force what will happen? Will it reflect the force entirely? Will it redirect into whatever the force field is anchored to? Will the force field move? Will the force field generator burn out?


Please, feel free to try and answer these questions or similar questions of your own!

The Grue
2013-07-04, 08:36 PM
Fun fact: "physical" forces are in fact electromagnetic forces. The resisting force you feel when you press your hand against the wall? That's the negatively-charged electrons in the atoms of your hand being repelled by the negatively-charged electrons in the atoms of the wall.

1) Both. There is no actual difference between a repulsive magnetic force and the contact force from "solid" matter. Non-pedantic answer: I would say a force field reacts like solid matter.

1a) See above. Non-pedantic answer: Works like a physical object, reacts as per Newton's Third Law; with as much force as is necessary to equalize inertia between the impacting object and the stationary object.

2) You could call it either way. Personally, I would consider the surface of a forcefield to be fairly smooth, but not perfectly smooth. Thus, an object in contact with the field's edge would experience a small amount of friction.

2b) Given the above, in theory yes but in practise no. You can't physically dig into the field like you could a rock wall, so you'd need to climb it using friction (which fails as soon as the force of gravity on your body exceeds the force of friction on your feet/hands), suction or, more feasibly, climb the way geckos do (http://geckolab.lclark.edu/dept/geckostory.html).

2c) Depends how thick the top of your force field is. If it's paper thin like I imagine the force fields in Star Trek being, no. If it's a 5-foot wall like D&D, sure, though you might have a hard time pushing off if it's too slippery.

3) Entirely up to you, I guess. Do you want force fields to be stronger or weaker than a pane of glass? Than a plank of wood? Than a sheet of iron? Than a plate of adamantium?

3a) Where a physical wall suffers a localized structural failure when something breaks through, I would have the force field "overload" entirely.

Douglas
2013-07-04, 08:46 PM
Does anyone know if you hurl a metal object into a strong enough magnetic field if the metal object will sustain structural damage from the impact or merely decelerate and stop dead?
That depends very much on how quickly the strength of the magnetic field changes with respect to location. If it's about the same strength at one end of the object as at the other, the object just decelerates and stops (and then accelerates back out if the field stays the same) without suffering damage. If it's a great deal stronger at the leading end of the object than the trailing end of the object, the object will suffer damage very similar to what would happen from colliding with a solid barrier.

The first case is roughly equivalent to your everyday experience with gravity, more specifically when something is flying through the air (such as with a ball that you just threw straight up) rather than resting on a surface. The second case, in the extreme variant of going from zero strength to very high strength in a micrometer or so, is actually exactly what really happens in the real world when an object hits a solid barrier.

Mnemnosyne
2013-07-04, 09:00 PM
Here are some good links discussing forcefields in sci-fi, they might be helpful:
http://www.projectrho.com/public_html/rocket/spacewardefense.php#forcefield
http://stardestroyer.net/Empire/Tech/Shields/Nature.html
http://stardestroyer.net/Empire/Tech/Shields/Impact.html

The answers to your questions therefore depend highly on exactly what technology you're using, and may not be universal even within the same campaign setting; there may be various forcefield technologies with different answers to those questions depending on which is being employed.

Tork
2013-07-04, 09:06 PM
1. Both or just one. A security field need only be a shock one. But to say keep air and items inside a spaceship you'd need a wall.

1a. If it is a wall type, it is a lot like hitting a wall. You could get all crazy sceince and say the field can absorb kentic energy. I don't think an object can be harmed by a magnetic field at all.

2.The idea would be that energy has no friction.

2a. Nope.

2b. Maybe

2c. Sure. There would need to be some sort of limit of weight. If you assume that the weight causes 'feedback' to the generator that is making the field.

3.As strong as the generator that is making it.

3a. Any of them.

TuggyNE
2013-07-04, 09:43 PM
I don't think an object can be harmed by a magnetic field at all.

As douglas said, it depends on the field; it's perfectly possible for a magnetic field to induce heating in a nearby object, and if there's enough of a gradient, the difference in force between ends of the object can distort or even destroy it. While such a severe gradient is quite difficult to achieve, it might be necessary for a force field effect.

valadil
2013-07-04, 10:01 PM
I don't like mixing magic and science. IMO something that alters reality isn't going to behave consistently when you start looking at the specifics. But if my players asked for a ruling, here's what I'd give them without spending too much time to think about it.

1: Does a force field behave like solid matter or does it behave more like a strong magnetic field that repels all matter?

Solid.

1a: How much impact does running into a force field generate? Is it any? Does anyone know if you hurl a metal object into a strong enough magnetic field if the metal object will sustain structural damage from the impact or merely decelerate and stop dead?

Yes. It will push back in order to repel the object. The force field will actually hit harder than a wall, because unlike the force field the wall has some give to it.

2: Does a force field have friction?

No.

2a: Is it possible to climb a force field?

No, not without friction. If you had some force moving you up, I guess you could glide up along the wall.

2b: If one is stuck on top of a horizontal force field can one push off it to escape or is one trapped?

No. What? I said these things aren't consistent, remember? This answer is because I've seen plenty of references to a horizontal force field working as a bridge. I've never seen them use one as a skating rink.

I'm also of the opinion that I'm not obliged to give the players an explanation for this. It's magic. That's what happens when you bend reality. Plus, why should they know? The characters don't know. Just because the characters have enough knowledge to be able to ask one of the secrets of the universe does not mean they know or understand the answer.

2c: Can a mobile force field be used to carry objects? Is there a weight limit?

Yes. If the players were giving me a hard time about friction, I might say something about angling the force field such that the object would slide off, and then they move the force field laterally such that the object remains on the field.

3: Just how strong is a force field?

Depends on the origin. IIRC correctly, Tenser's Floating Disc is a mobile force field. It is not as strong as a Wall of Force. In sci-fi, it would depend on the equipment generating the force field and the power source keeping it up.

3a: If hit with a huge force what will happen? Will it reflect the force entirely? Will it redirect into whatever the force field is anchored to? Will the force field move? Will the force field generator burn out?

Magic usually reflects the force. Sci-fi might let it override the origin.

Mastikator
2013-07-04, 11:45 PM
I would treat a force field as highly charged plasma contained in a magnetic field.

1 So, not solid, more like gaseous that disintegrates anything it touches.

1.1 There's no impact more than there is impact walking into fire, however anything that can be magnetized will be hurled out from the magnetic field.

2 Virtually no friction unless you crash into it really fast (like splashing into water), with enough isolating material protecting you you could walk through the field.

2.1 no

2.2 you'd fall into it and probably not come out on the other side, depending on its strength.

2.3 nope, it can only be used to stop energy attacks and extreme velocity ballistic attacks.

3 the magnetic field would have to be extremely strong, probably tens of thousands of newtons. And tens of millions of degrees hot, can only be used in space.

3.1 you'd be disintegrated without protection.


In settings like Star Trek and Star Wars force fields are never described as being anything, you simply see them and they seem to work like a solid sheet of glass that zaps you if you touch it.

NichG
2013-07-05, 12:26 AM
Lets consider two kinds of forces that could give a repulsion effect.

One type is something like a concentrated area of high winds constantly pushing outward. If something shoves against it very hard, it just goes through because the wind is insufficient to deflect it. There won't be much impact because the wind exerts force over the entire thickness of the 'field', which is very very large compared to the distance over which forces from, say, a slab of concrete stop something hitting it. As far as what happens to momentum 'absorbed' by the field, its carried away by the constantly moving packets of air that comprise the field, so it would have no real effect on the point of origin (on the other hand, the point of origin will experience a constant backward push due to having to emit the wind in the first place, but this could be solved by placing the emitter between two directional surfaces of the force field). If you tried to stand on this field you'd fall through and be blown back one way or the other.

Instead of wind, this could be any kind of force-carrying thing - light, magic particles, whatever. The point is that the force is coming from something that is actually in place where you're touching it, rather than somehow being rigidly connected to the emitter.

The second type of force field is some kind of 'static' field, like you might get between a static charge and an object with a different charge (or between a magnetic field emitter and metal objects). The major difference between this and the type 1 field is that the area of the field is directly attached to the point of origin. Push on the field and you push directly on the origin point. Slam into it with tons of momentum and the origin point will pick up that momentum (and if its fixed in place, it might destroy itself against whatever is holding it in place depending on how evenly it can distribute the force).

Physically the difference is basically just where the momentum of an object interacting with the field is dissipated to. In Type 1, its dissipated into material that then interacts with the environment and deposits the momentum around the edges of the field (so e.g. if you slammed into a field like that and were bounced off, there might be an explosion of dust from the edges or something). In Type 2, its transmitted directly to the emitter. Another way to think of it is to ask 'how rigid is the coupling between emitter and field'. Type 1 is infinitely slack, whereas Type 2 is infinitely rigid. Both cases still conserve momentum.

Ashtagon
2013-07-05, 03:13 AM
My personal take on it is that D&D force fields are solid and impermeable to anything except ordinary light. They have about the same friction properties as glass. So you can walk on a horizontal wall of force, but you can't climb up a vertical one. Also, they don't accept pitons or similar climbing aids, and they remain solid and featureless unless and until they collapse completely.

SF force fields? GURPS ultra-tech is your best reference here. They have more flavours of force field than you can shake a light sabre at.

hamishspence
2013-07-05, 07:04 AM
Here are some good links discussing forcefields in sci-fi, they might be helpful:
http://www.projectrho.com/public_html/rocket/spacewardefense.php#forcefield
http://stardestroyer.net/Empire/Tech/Shields/Nature.html
http://stardestroyer.net/Empire/Tech/Shields/Impact.html

While I'd treat anything said by SD.net with a certain amount of caution- the basic points made do seem to make sense in this case.

Longes
2013-07-05, 07:08 AM
The simple answer here would be: "You are right, this technology is impossible. And so is this ship. Because it's an impossible ship, it suddenly stops working and you all die."

An even simpler answer would be: "Show me the math proving that you are right."

Autolykos
2013-07-05, 08:02 AM
Basically, it's magic. It doesn't have to make sense, it just needs to be consistent. For SciFi, any sufficiently advanced technology...
My personal take on it is this (but it's your setting, you can make them any way you like):

1: Like a solid wall. It says so in most rules, and it behaves that way in pretty much any SciFi setting I know. For pseudo-scientific explanations, look above.

1a: As much as you put into the object. What Newton said is not just a good idea, it's the law. The force field generator would still need to compensate the change in momentum, which could make the field fail if it's enough. It could probably be built to absorb energy, but there isn't much use in it (and that energy needs to go somewhere).

2: A perfectly flat force field wouldn't, but it may not be feasible to generate one. I'd go with very low friction, like ice or glass.

2a: Without tools, no (unless you use magic, but then you're probably flying and not climbing). Suction may or may not work on a gas-tight force field, and will definitely fail on one that is not. Using Van-der-Waals forces like a gecko may or may not work, depending on how the field's potential looks on a micro scale (I'd call no unless you really want it to work). In a SciFi setting, there might be special tools developed for climbing force fields, though.

2b: You can, but you won't be able to jump higher than pushing off the ground. Unless the field is built to absorb energy, then you can not.

2c: Sure, but then you need to carry the weight of the force field generator, plus the weight of the objects. Unless you also have some kind of anti-gravity technology.

3: As strong as you want it to be. It will definitely fail if you apply enough force to rip the generator out of the structure it's built into, or if you make it absorb enough energy that the generator overheats. When that happens is your call.

3a: That question is hard to answer generally. What happens when you hit a brick wall with a "large enough" force? I'd rule that the force field ceases to exist *after* the generator goes offline, and will absorb as much energy or change as much momentum as it can take before that happens. But it could have a safety overload that switches it off before the generator gets damaged.

CombatOwl
2013-07-05, 01:06 PM
In my games players frequently try and apply real world physics to a magical / sci fi situation to create some sort of an exploit. If I tell them it doesn't work like this, then they pick apart the entire technology and insist that if it doesn't work their way it doesn't work at all. I see a lot of similar arguments on this forum.

"Forcefields in this world operate by the art and science of unicorn farts and happy thoughts. It is an infinite supply of power, sadly usable only for force fields."


The most common offender is force fields of various sorts. Either those created by the D&D Wall of Force spell or a Sci Fi forcefield like what the Enterprise uses to seal breaches or restrain prisoners on Star Trek.

So, I would like to ask a few questions about people's opinions on Force Fields and the physics behind them:

1: Does a force field behave like solid matter or does it behave more like a strong magnetic field that repels all matter?

Force fields don't exist in the real world, so that's basically up to the DM to determine unless the setting establishes that already.


1a: How much impact does running into a force field generate? Is it any? Does anyone know if you hurl a metal object into a strong enough magnetic field if the metal object will sustain structural damage from the impact or merely decelerate and stop dead?

2: Does a force field have friction?

That would be up to the DM to determine, unless the setting establishes that detail for him.


2a: Is it possible to climb a force field?

I can't imagine any sort of setting where a force field would be climbable, but that's more reflecting my own interpretation.

JusticeZero
2013-07-05, 01:19 PM
1: Does a force field behave like solid matter or does it behave more like a strong magnetic field that repels all matter?The second.
1a: How much impact does running into a force field generate? Is it any? Does anyone know if you hurl a metal object into a strong enough magnetic field if the metal object will sustain structural damage from the impact or merely decelerate and stop dead?Structural damage is from inertial force. You don't have to actually "impact" anything to be damaged by an impact; the fact that the object is decelerating does the damage, not the hitting of a physical thing.
2: Does a force field have friction?
2a: Is it possible to climb a force field?
2b: If one is stuck on top of a horizontal force field can one push off it to escape or is one trapped?
2c: Can a mobile force field be used to carry objects? Is there a weight limit?A force field does not have friction, but it is unlikely to be perfectly flat. If you are on top of a force field, in a concave, then you have no way of moving; it's a bit like the magnet chamber (http://io9.com/5355779/a-mouse-defies-gravity-using-nothing-but-magnets) that they put animals into to study zero gravity. This drains power; it is not more efficient to use the field to carry things than to use a crane; the field is just to apply the force in a way that is more useful for certain things. This also explains 3; it is at best as strong as the power source that powers it's ability to put power from the generator and capacitors through the cables to accelerate objects away from the field, and if the force is higher than the rated output, the object will pass through with the remaining vector of speed. The force field generator can get pushed around by pushing on the field.

This is for sci-fi force fields. Magic walls of force I give the same fluff that I give walls of ectoplasm: A partial, timeless, virtual object. A physical object, in this case a stone or metal or wooden wall, is willed to appear in a space. The power backing this does not have the power to create matter, but can (temporarily) write the existence of a material wall frozen in time into the space. The object lacks material form, and more importantly has no time to be altered by anything. It is a "glitch" effect. That said, the object has the friction, etc of the model object. Destroying the wall causes it to be dispelled.

Douglas
2013-07-05, 03:32 PM
The second.Structural damage is from inertial force. You don't have to actually "impact" anything to be damaged by an impact; the fact that the object is decelerating does the damage, not the hitting of a physical thing.
There's an important distinction here: the fact that the object is decelerating non-uniformly does the damage. Damage is caused by different parts of the object experiencing different accelerations.

Jay R
2013-07-05, 05:06 PM
In my games players frequently try and apply real world physics to a magical / sci fi situation to create some sort of an exploit. If I tell them it doesn't work like this, then they pick apart the entire technology and insist that if it doesn't work their way it doesn't work at all. I see a lot of similar arguments on this forum.


Before asking any specific questions, the general answer is that science does not work in this world.
1. If a wizard can make a lightning bolt by the force of his mind, then energy is not conserved.
2. Any creation spell proves that matter is not conserved.
3. Flying dragons or stone gargoyles are proof that the cube-square law doesn't work.
4. Flight, Levitation or Feather Fall all prove that gravity is not constant.
5. Raise Dead, Resurrection, creation spells, etc. prove that entroy is not always increasing.

In short, the best answer to any such question is that the player is assuming constancy of laws that are provably not constant.

Now, on that basis, here's how I would answer my players. [In brackets is the underlying decision I would ultimately apply.]


1: Does a force field behave like solid matter or does it behave more like a strong magnetic field that repels all matter?

Your character has heard rumors about all sorts of fields - except magnetic, of course. Tenser's Floating Disc clearly doesn't repel all matter. If you want to experiment with the field in front of me, tell me what experiment you try, and I'll tell you the effects.

[In fact, on the subatomic level, matter behaves like a field that repels other matter. If you lean on a wall, your atoms aren't actually touching the wall's atoms. It will behave like matter, but have no temperature, texture, or other properties of touch.]


1a: How much impact does running into a force field generate? Is it any? Does anyone know if you hurl a metal object into a strong enough magnetic field if the metal object will sustain structural damage from the impact or merely decelerate and stop dead?

Who's running into the force field, and at what speed, and in what armor?

[I will give them the same damage they'd get running into a granite wall.]


2: Does a force field have friction?

Describe this question in terms your character knows, and then tell me how you plan to test it.

[Not in the normal sense, but rubbing it might release some energy, depending on the field.]


2a: Is it possible to climb a force field?

Who's trying it, and how many hit points does he have?

[No, of course not. There's nothing to hold onto.]


2b: If one is stuck on top of a horizontal force field can one push off it to escape or is one trapped?

Try it and see. You have read no text on this subject.

[Neither, of course. The way to get off a more-or-less frictionless surface in our world is to throw some object in one direction, and you will slide in the other direction. But this assumes that momentum is preserved. Feel free to make a different assumption. Rememnber that fields are magic, which is not consistent.]


2c: Can a mobile force field be used to carry objects? Is there a weight limit?

Try it!
[The 1E and 2E spell Tenser's floating disc did exactly this, and gave the limits. Unless the spell description says it can, then it can't.]


3: Just how strong is a force field?

3a: If hit with a huge force what will happen? Will it reflect the force entirely? Will it redirect into whatever the force field is anchored to? Will the force field move? Will the force field generator burn out?

What experiment do you try to find out. How far back are the rest of the party standing when you try it?

[The spell description tells what the spell does.

The point is this. There are no books of physics texts describing magic, and unless they know somebody who has tried this in the past, the only way they can find out is to try it.

If you give them physical principles instead of answers to experiments, they will try the games they've been trying. Let them take risks if they want answers. They will soon lose much of their curiosity.

Lapak
2013-07-05, 05:32 PM
Hmm, OK. This is amusing enough that I'm going to try to
A) violate my own general policy by giving magic a pseudo-logical mechanism for operation, and
B) try to do it in a way that hasn't been suggested yet in this thread.

1: Does a force field behave like solid matter or does it behave more like a strong magnetic field that repels all matter?
Neither. A force field, while apparently two-dimensional, actually creates an artificial-but-infinite empty space between one side of the effect and the other. While there's nothing actually there, crossing the barrier would take an infinite amount of time. Pure light, being the one thing that travels outside of time and covers all distances instantly (magical physics!) can cross this barrier without trouble; everything else that tries to move into the barrier runs out of range and/or kinetic energy long before reaching the "other side."

1a: How much impact does running into a force field generate? Is it any? Does anyone know if you hurl a metal object into a strong enough magnetic field if the metal object will sustain structural damage from the impact or merely decelerate and stop dead?
None. Objects aren't stopped dead by the field, despite appearances; they simply run out of range and/or motive energy and either burn out (in the case of, for example, a lightning bolt) or drop straight down on the same side of the field they originated on (in the case of a physical projectile.) A creature (or object that is held off the floor, like a rolling cart) simply halts.

2: Does a force field have friction?
Not as such. There's nothing there to have friction against. Objects in contact with a force field are affected normally by gravity; an object resting on a horizontal force field is effectively suspended in endless, motionless free-fall. The sensation of pressing up against a force field is unsettling for most intelligent and semi-intelligent beings, as the physical sensation of absolute emptiness wars with the apparent affect of being stopped dead.

2a: Is it possible to climb a force field?
No. There is nothing to grip and no way to force a handhold into the field.

2b: If one is stuck on top of a horizontal force field can one push off it to escape or is one trapped?
Assuming that one is unable to make contact with anything that isn't the forcefield AND has no mode of movement other than by contact with a surface, one would be trapped.

2c: Can a mobile force field be used to carry objects? Is there a weight limit?
Yes to the first; generally no to the second (other than the obvious limits created by trying to usefully pile things up on such a surface and the apparent size of the field.)

3: Just how strong is a force field?
Strength isn't an issue, since the body of the field is an infinite empty space; there's nothing to hit or destroy. Only attacking the enchantment (or in sci-fi, the projector that generates the field) itself with specific countermeasures will break down such a field before it expires normally.

3a: If hit with a huge force what will happen? Will it reflect the force entirely? Will it redirect into whatever the force field is anchored to? Will the force field move? Will the force field generator burn out?
No, no, and no. As long as the field is up, any attacking force will simply spend itself in the theoretical empty space of the field. Only specific countermeasures that target the effect itself, rather than simply throwing raw energy or matter at the field, will bring it down.

Talakeal
2013-07-05, 05:51 PM
Lots of great stuff.

That's brilliant. That solves nearly all of the problems I was having with people using rl physics exploits with a vertical wall of force.

Of course, for horizontal walls of force it makes them much worse. Not only would it be a perfect prison / pack mule, but it can also imbue objects with virtually infinite amounts of kinetic energy due to gravity, unless I missed something, which is very possible. Any solution to that?

Lapak
2013-07-05, 06:45 PM
That's brilliant. That solves nearly all of the problems I was having with people using rl physics exploits with a vertical wall of force.

Of course, for horizontal walls of force it makes them much worse. Not only would it be a perfect prison / pack mule, but it can also imbue objects with virtually infinite amounts of kinetic energy due to gravity, unless I missed something, which is very possible. Any solution to that?Hmm. Well, as for the infinite-kinetic-energy business I wouldn't worry, as it is (in essence) a motionless free fall since you can't actually make any real progress. You're falling into non-space, not into a gravity well, so you're not actually accelerating at all in a practical sense; remember that you're not actually moving in good old 'XYZ' coordinates. All of your speed is accumulated and/or spent in the W direction that the spell creates. So when the effect terminates you're shunted out of non-space onto the side of the field you started on with zero speed. The pack-mule issue is limited as I said; however good a packer you may be you can only load so much onto a platform the size of a Tenser's Floating Disc before stuff falls off. It's nice, but not game-breaking. Plus there's no real way to avoid the fact that the stuff is going to fall down when the effect ends unless you're quick enough to unload it, which creates new problems transportation-wise if there's anything breakable involved.

EDIT: For two points of clarification: to be absolutely clear, yes you are falling and accelerating when you're resting on a horizontal field, but you're accelerating in a direction that ceases to exist when the spell stops. Which is from a practical standpoint 'not accelerating at all.' And increasing the size of a pack-mule field to get around packing issues creates its own problems: trying to load or unload things on a surface wider than twice arm's length which you cannot stand on safely becomes a significant challenge. [/edit]

Or the simplest resolution is to declare that force fields oriented parallel to a gravity field can't exist due to the nature of the effect that creates the field. Perpendicular-to-gravity (that is, straight up-and-down walls) and spherical effects (which are self-supporting) only. No more prison-planes, because a prisoner will slip right off a sphere.

Talakeal
2013-07-05, 09:42 PM
More good stuff.

That's a good idea about directions, although I can't say for sure how it would work "realistically", it is certainly good enough for the game.

The problem is that I am using a somewhat open ended magic system, where the precise variables of the spell are fluid. Players are creating horizontal force fields and using them as immobilization traps, or making mobile force fields and using them as infinite capacity mules.

By saying that a force field must be oriented in a certain direction or must be stationary I am placing in a lot of arbitrary restrictions which disrupt an otherwise elegant spell system.

Lapak
2013-07-05, 10:11 PM
That's a good idea about directions, although I can't say for sure how it would work "realistically", it is certainly good enough for the game.

The problem is that I am using a somewhat open ended magic system, where the precise variables of the spell are fluid. Players are creating horizontal force fields and using them as immobilization traps, or making mobile force fields and using them as infinite capacity mules.

By saying that a force field must be oriented in a certain direction or must be stationary I am placing in a lot of arbitrary restrictions which disrupt an otherwise elegant spell system.I wouldn't worry too much about it even if you keep any-direction force fields; so long as you enforce the natural problems with flat, frictionless carry-fields they'll be of limited utility, and using them as immobilization traps would be tougher than you think. Assuming - as, for example, Wall of Force does - that you can't create them in an occupied space, creating one underneath someone who is standing on a surface isn't possible. Assuming that they have to be a solid plane - and I can't see THAT as unreasonable, considering what they are - you can't encircle someone with one, either. (Englobe them, possibly; encircle them, no.)

And in any event, in any situation where forcefield-on-demand is available to your players their opposition is probably either potent enough to have a countermeasure (flight, long reach, a grapple-gun, Gust of Wind, a Decanter of Endless Water, harpooning a PC, etc.) or insignificant enough that they wouldn't be too troublesome anyway.

And if need be, 'must be stationary' is WAY the easiest limitation to justify in my model; creating infinite non-space in a set location is quite mad enough without justifying a mobile version of the effect. If you have Tenser's or an equivalent, that may be another effect altogether; the main rules of 3e don't support hiding under a Tenser's as a shield of invulnerability or even imply that it's indestructible.

Talakeal
2013-07-05, 10:56 PM
Most people dont have pcs like mine. They absolutely have used tensers floating disk as an impenetrable shield / obstacle and argued the "physics" would make it impossible to use as a mule if it didnt also fulfil those roles.

The New Bruceski
2013-07-05, 11:15 PM
Tenser's has a weight limit, therefore it is not indestructible. Max weight divided by area is the force required to break through. Let me just check the SRD...

3 feet diameter, 100lbs per level. Area is pi*18^2=about 1018 square inches, so it can withstand a tenth of a pound per square inch per caster level. You could punch through it even at 20th level.

Lapak
2013-07-05, 11:47 PM
Most people dont have pcs like mine. They absolutely have used tensers floating disk as an impenetrable shield / obstacle and argued the "physics" would make it impossible to use as a mule if it didnt also fulfil those roles.Well, the biggest problem with THAT has nothing to do with the indestructibility and everything to do with the fact that it's only about as big as a large shield. 3' diameter isn't enough for ONE person to hide completely under, let alone a party, plus it hovers 3 feet off the ground so it's useless against anyone who is at a similar elevation to you. I'd go ahead and give whoever single character was cowering under it bonuses as if using a large shield against anyone who was substantially above them (or equal height and in melee with them, I suppose; if you want to take -4 to AC in order to gain +1 to AC against a melee attacker, that's your choice I guess) and leave it at that. Hardly game-breaking.

Autolykos
2013-07-06, 04:39 AM
Most people dont have pcs like mine. They absolutely have used tensers floating disk as an impenetrable shield / obstacle and argued the "physics" would make it impossible to use as a mule if it didnt also fulfil those roles.And they're right to argue that way. The spell's other limitations make it a poor shield, but it should be able to block attacks in principle. Even though magic is by definition violating the laws of nature, it should do so as little as possible. Otherwise, you will quickly find yourself in a world full of contradictions where nothing makes sense. As soon as I'd see that coming, I'd have a good OOG talk about it, and if that doesn't help, I'd leave. Unless, of course, the premise of the game includes an inconsistent world like Toon or Paranoia.
With SciFi, doing stuff like that is usually even worse. You can probably get away playing fast and loose with quantum mechanics or relativity, as it will be hard for player actions to expose inconsistencies in them. But once you start to repeatedly kick Newton (or, for that matter, Boltzmann) in the balls, there won't be much consistency left to salvage, even though you might not see the problem immediately. It won't be long until the physics that model your world are contorted like an Escher painting, and you'll have to end every argument about the world with "because I say so" because no explanation would make sense.
But just because your world has consistent rules does not mean you need to tell them to your players right away. I think Jay R has the best advice in the whole thread. Let them try it out. It's more fun than telling them, and makes it less likely that you'll have to make inconsistent rulings. But if you do and they notice, they'll probably feel cheated. I definitely would.

Talakeal
2013-07-06, 05:31 AM
And they're right to argue that way. The spell's other limitations make it a poor shield, but it should be able to block attacks in principle. Even though magic is by definition violating the laws of nature, it should do so as little as possible. Otherwise, you will quickly find yourself in a world full of contradictions where nothing makes sense. As soon as I'd see that coming, I'd have a good OOG talk about it, and if that doesn't help, I'd leave. Unless, of course, the premise of the game includes an inconsistent world like Toon or Paranoia.
With SciFi, doing stuff like that is usually even worse. You can probably get away playing fast and loose with quantum mechanics or relativity, as it will be hard for player actions to expose inconsistencies in them. But once you start to repeatedly kick Newton (or, for that matter, Boltzmann) in the balls, there won't be much consistency left to salvage, even though you might not see the problem immediately. It won't be long until the physics that model your world are contorted like an Escher painting, and you'll have to end every argument about the world with "because I say so" because no explanation would make sense.
But just because your world has consistent rules does not mean you need to tell them to your players right away. I think Jay R has the best advice in the whole thread. Let them try it out. It's more fun than telling them, and makes it less likely that you'll have to make inconsistent rulings. But if you do and they notice, they'll probably feel cheated. I definitely would.

Wow. Its refreshing to find someone online who actually agrees with my PCs, and takes it one step further. I don't think I have ever met someone who would feel cheated or leave the game over a DM insisting that spells do what RAW says they do before.

The problem with that line of thinking is, where do you stop? The game is full of places where the rules are either an abstraction or are trying to describe something for which the laws of physics have no explanation.

For example:

Dragons are far too heavy to fly. Humans cannot survive immersion in lava no matter how tough. Energy cannot be created or destroyed. A dagger can kill any man in one hit. Every action has an equal and opposite reaction. One cannot expend more calories than one takes in, and cannot regenerate tissue in excess of available food.

All of these things are flat out impossible using physics as we know them, yet the rules say they are possible.

Likewise the rules say absolutely nothing about how strong tenser's floating disk is. It might be impenetrable, or it might be as weak as wet tissue paper. There are no game rules to base this off of, and there are no real life examples to use.

Likewise I once had a player who tried transforming a thrown rock into gold mid flight, arguing that increasing the mass while keeping a constant velocity would greatly increase its momentum and the damage of impact. Another player said that was nonsense, it would be momentum that would remain constant and the velocity would decrease accordingly, causing the rock to harmlessly fall short*.

Who was right? Who the heck knows? They are describing a situation that is literally impossible in the real world, thus physics has no answer. Likewise the game designers never wrote rules for it.

I am not sure if it is reasonable to try and insist physics work a certain way in regards to an effect that is literally impossible. Take for example Teleport. If you used it to travel instantly from the pole to the equator you would, in the real world, be thrown to the ground and torn to pieces by the difference in rotational velocity. If the DM declared your PC dead as a result of that, would you say "Well, that's physics. Time to reroll,"? Or would you argue that the magical teleportation doesn't have any RAW or fluff mention of shredding people like that, and thus the spell must not work that way?
What if I said that the next time you cast a wall of force it stopped the planet dead in its tracks and caused an apocalypse? Because the wall of force says it is completely immobile and impenetrable, and it says nothing about taking a planet's orbital momentum (or indeed the momentum of the rest of the universe) into account.

If anything assuming a Tenser's Disk is an effective shield, let alone an invincible one, actually has LESS support, both in physics and in RAW, than killing people through teleportation velocity.

Its the kind of thinking that leads to the commoner rail gun, something that conveniently ignores some physics and some RAW, and then puts what is left together again in an exploitative fashion.




Well, the biggest problem with THAT has nothing to do with the indestructibility and everything to do with the fact that it's only about as big as a large shield. 3' diameter isn't enough for ONE person to hide completely under, let alone a party, plus it hovers 3 feet off the ground so it's useless against anyone who is at a similar elevation to you. I'd go ahead and give whoever single character was cowering under it bonuses as if using a large shield against anyone who was substantially above them (or equal height and in melee with them, I suppose; if you want to take -4 to AC in order to gain +1 to AC against a melee attacker, that's your choice I guess) and leave it at that. Hardly game-breaking.

IIRC the players cast an enlarged tenser's disk (I don't know if that is RAW legal, but as I said I use a homebrew metamagic system) to block a trapdoor and trap some enemies in a burning room while they sat safely below.




Tenser's has a weight limit, therefore it is not indestructible. Max weight divided by area is the force required to break through. Let me just check the SRD...

3 feet diameter, 100lbs per level. Area is pi*18^2=about 1018 square inches, so it can withstand a tenth of a pound per square inch per caster level. You could punch through it even at 20th level.

While I appreciate the math, the spell never says whether that is the force required to break the disk or merely overtax its capacity for movement.

I believe your calculations assume that all weight MUST be distributed perfectly evenly, which is of course fairly ridiculous. There is no RAW support for that, and it makes the spell useless as one couldn't realistically load the disk without puncturing it.



*: A similar anecdote. I have a homebrew spell that instantly changes the facing of the target. The RAW use is to knock a standing person prone or vice versa, or allow a flying creature with poor maneuverability to execute an instant turn.
One of my players insisted on using the spell to turn an enemy's attacks around on them in midair. I said the spell doesn't work that way, and all it would do is cause the projectile to strike the same target blunt end first. The player insisted the spell MUST also redirect all momentum in the new direction, otherwise using it for an on the spot turn would be impossible, and using it on someone in motion would send them tumbling backwards as all their forward momentum is now going in the opposite direction.
I tried to say that it was magic and that newton's laws could be hand waved (as the are in the above teleportation example), but the player refused to back down, so I had to end up raising the spell level to a point where using it to shoot back arrows was reasonable, and was far too high for its intended purpose, for which it was never cast again.
It seems to me that arguing that magic, something which already violates the laws of physics and has tons of built in game balance checks for no reason (say not being able to summon creatures in midair or being able to create matter out of nothing but not an equivalent amount of pure energy), follows some reasonable measures of balance and common sense is hardly game breaking or cheating.

TuggyNE
2013-07-06, 06:09 AM
A similar anecdote. I have a homebrew spell that instantly changes the facing of the target. The RAW use is to knock a standing person prone or vice versa, or allow a flying creature with poor maneuverability to execute an instant turn.
One of my players insisted on using the spell to turn an enemy's attacks around on them in midair. I said the spell doesn't work that way, and all it would do is cause the projectile to strike the same target blunt end first. The player insisted the spell MUST also redirect all momentum in the new direction, otherwise using it for an on the spot turn would be impossible, and using it on someone in motion would send them tumbling backwards as all their forward momentum is now going in the opposite direction.
I tried to say that it was magic and that newton's laws could be hand waved (as the are in the above teleportation example), but the player refused to back down, so I had to end up raising the spell level to a point where using it to shoot back arrows was reasonable, and was far too high for its intended purpose, for which it was never cast again.

For what it's worth, I'd just rejigger the spell so it couldn't be cast on objects. Problem solved, albeit inelegantly.

Lapak
2013-07-06, 06:46 AM
IIRC the players cast an enlarged tenser's disk (I don't know if that is RAW legal, but as I said I use a homebrew metamagic system) to block a trapdoor and trap some enemies in a burning room while they sat safely below.Hmm. Some significant problems with that theory...

*: A similar anecdote. I have a homebrew spell that instantly changes the facing of the target. The RAW use is to knock a standing person prone or vice versa, or allow a flying creature with poor maneuverability to execute an instant turn.
One of my players insisted on using the spell to turn an enemy's attacks around on them in midair. I said the spell doesn't work that way, and all it would do is cause the projectile to strike the same target blunt end first. The player insisted the spell MUST also redirect all momentum in the new direction, otherwise using it for an on the spot turn would be impossible, and using it on someone in motion would send them tumbling backwards as all their forward momentum is now going in the opposite direction.
I tried to say that it was magic and that newton's laws could be hand waved (as the are in the above teleportation example), but the player refused to back down, so I had to end up raising the spell level to a point where using it to shoot back arrows was reasonable, and was far too high for its intended purpose, for which it was never cast again.
It seems to me that arguing that magic, something which already violates the laws of physics and has tons of built in game balance checks for no reason (say not being able to summon creatures in midair or being able to create matter out of nothing but not an equivalent amount of pure energy), follows some reasonable measures of balance and common sense is hardly game breaking or cheating.Yep, that second anecdote confirms for me that the problem is less with the group and more with you letting the group walk all over you. As you mentioned earlier in the post, they're cherry-picking what they want physics to apply to and what they don't and even making up suggestions that make no physical sense; an instant reversal of a moving target would have all kinds of momentum issues but a complete reversal of it makes no logical sense whatsoever. That crosses the line from "trying to make a sensible argument" into "but I want this to do something it shouldn't" and if you aren't willing to say no to THAT then you are going to have never-ending problems. That one isn't even an issue of saying "it's magic, it doesn't work that way;" it jumps right past that into "no, what you are suggesting is not logically consistent EVEN IF we assume that the spell works on the gross physical level in the way you are imagining."

Which last isn't a safe assumption anyway! Aside from that, it suffers from the usual laziness in terms of assuming that targeting is magical just because it's a spell.
- Perhaps the effect takes more than a fraction of a second to kick in, and something moving fast enough (like a projectile) isn't still long enough to effect.
- Perhaps the spell requires that the caster state an exact position for their target, which is impossible for a swiftly-moving object
- Perhaps the spell uses the soul and/or consciousness of the target to define the boundaries of the spell effect (which is to say, it can only target a creature.)

It's worse than the nearly-universal assumption that a wizard can just eyeball the placement for the origin point of a 40' sphere such that it hits all the enemies fighting his front-line defenders but doesn't touch the defenders themselves. Unless he's laid down a marker on the ground before the fight, that's a pretty demanding mental calculation.

The Tenser's thing I might let them get away with, if we had decided that the height of the thing could be adjusted - there's no way that a disk 3 feet off the ground is doing much to block a trapdoor - but assuming that's possible also makes a lot of assumptions about the Disk that may or may not be true.

Getting back on point, you need to learn to say No and make it stick, because the 'reverse facing' argument is less 'this makes physical sense' and more 'I want it to do something there is no basis for it to do.'

Autolykos
2013-07-06, 07:27 AM
Wow. Its refreshing to find someone online who actually agrees with my PCs, and takes it one step further. I don't think I have ever met someone who would feel cheated or leave the game over a DM insisting that spells do what RAW says they do before.I'm not saying that physics should override RAW. I'm even ok with RAW sometimes violating physics, as far as magic is concerned. My point is just that this should be kept to an absolute minimum, and everything not explicitly mentioned in RAW (or your house rules) should behave consistent to the rules governing our world.
The primary effects of magic (like the wizard throwing a lightning bolt) are allowed to walk all over physics. That's fine, it's magic. But you'll save yourself a lot of headaches if the secondary effects (does that lightning bolt produce heat or sound?) are consistent with real-world physics.
If you want a metaphysical excuse for what magic can do, I'd just postulate that it connects to a quasi-plane that acts as energy source, entropy sink or reaction mass, depending on what your spell needs. The spell maintains that connection and is able to transfer a finite amount of whatever it needs to produce its effects. And stuff outside the direct effects of the spell does not have access to this, and thus has to obey physics as we know it. For creatures behaving inconsistent with physics, they probably have an "implicit" SLA that lets them ignore these specific effects and can't be dispelled.
In SciFi, that "quasi-plane" should be replaced by a power cable, some large mass (like a spaceship or planet) and some place to blow excess entropy to (like anywhere outside).
And where RAW leads to completely ludicrous results (like the commoner rail gun) you should be fine with saying that RAW is inconsistent and you won't use it that way. But that's a house rule, and I think it's bad form to make up house rules as you go if you can avoid it, especially if it's just to foil their plans.
In your example of using Tenser's Floating Disc to block a trap door, I'd congratulate them on their creativity (if they can explain how they would move the disc in a position that can block it). It's however reasonable to assume that the disc can't generate more force that what it can normally carry, so if the monster is stronger than that, it will push the disc out of the way.
On an additional note, your world doesn't actually have to follow our physics. It just needs to be consistent in itself, and the players should at least be able to have some intuition about stuff their characters experience regularly. And the easiest way to build such a system and be reasonably sure it's non-contradictory is copying at least Newtonian physics and probably also thermodynamics from our world.

EDIT: Please don't think I'm blaming you for stuff going wrong with your group. You seem to have at least one player I couldn't be bothered to game with. If that's the one starting these discussions, he might be doing it just to annoy you, and not for any good reasons.
But I've had some bad experiences with a DM in the past who would arbitrarily change the way his world behaves whenever we tried to do something that wouldn't fit "his" plot. That led to some conflict, and I'd imagine his version of what happened would look quite a lot like some of your posts in other threads, had he posted it to some Internet forum. I have some theories on how these conflicts come about, but that would probably derail this thread.

Anonymouswizard
2013-07-06, 09:50 AM
1: Does a force field behave like solid matter or does it behave more like a strong magnetic field that repels all matter?
Why assume that there is just the one type of force field? Lets assume we have two types of force fields, one is a 'Repulsive Force Field' that repels matter, and the other is an 'Invisible Matter Force Field' that behaves like matter. For preference I would use an IMFF as it feels like harder science when using strong force fields (solid objects are just lots of points of mass surrounded by force fields), and if force fields behave like matter we could have 'solid' force fields that act like walls and 'liquid' force fields that just require greater effort to move through (and act like most 'repulsive' force fields).


1a: How much impact does running into a force field generate? Is it any? Does anyone know if you hurl a metal object into a strong enough magnetic field if the metal object will sustain structural damage from the impact or merely decelerate and stop dead?
again, why are all force fields the same. Our 'liquid IMFF' has less impact than our 'solid IMFF', but both would kill you if you ran fast enough.


2: Does a force field have friction?
Does it provide a normal reaction force? If so then yes, but the coefficient of friction may not be noticeable. Depending on your force field it could be anywhere from practically 0 t better than normal ground.


2a: Is it possible to climb a force field?
No, due t smoothness, but it may be possible to travel up an inclined force field, even up an almost vertical one if the coefficient of friction is great enough.


2b: If one is stuck on top of a horizontal force field can one push off it to escape or is one trapped?
Stand on the ground. Can you push up on it? If the coefficient of friction is great enough then you can apply the force you need, assuming the local g isn't too much for you to handle.


2c: Can a mobile force field be used to carry objects? Is there a weight limit?
Yes and yes, but you could increase the weight limit in theory by adding more mass.


3: Just how strong is a force field?
Varies. A solid force field will give way if enough force is applied, and depending on the maker and their technology will either keep the hole, move the remaining Invisible Matter to end up with a slightly weaker force field, or just repair itself to full strength.


3a: If hit with a huge force what will happen? Will it reflect the force entirely? Will it redirect into whatever the force field is anchored to? Will the force field move? Will the force field generator burn out?
It will act like matter does. It will absorb as much force as it can, and then the bit hit will move. The generator will not take significant damage unless hit itself.

Jay R
2013-07-06, 11:47 AM
The problem with that line of thinking is, where do you stop? The game is full of places where the rules are either an abstraction or are trying to describe something for which the laws of physics have no explanation.

So the DM makes a ruling about how it works. For instance:


Dragons are far too heavy to fly.

So are wizards. Therefore the assumption that gravity is a universal force is provably false. Dragons are magical creatures, and one of their abilities is to fly.


<other examples>

All of these things are flat out impossible using physics as we know them, yet the rules say they are possible.

Right. So every one of these is proof that your players' logic is wrong. It is based on the assumption of consistent physical laws, and the laws of physics are not consistent when acted uipon by the forc es of magic.

Every single time they try to use a spell in a way the rules don't allow, the response needs to be some version of, "It doesn't work. If you make a Knowledge (Arcane) check, you will remember that magical forces are capricious, inconsistent, and untrustworthy. If you want to research a spell that does that, you may attempt to do so. But until you have a spell with that effect, you do not have a spell with that effect."


Likewise I once had a player who tried transforming a thrown rock into gold mid flight, arguing that increasing the mass while keeping a constant velocity would greatly increase its momentum and the damage of impact. Another player said that was nonsense, it would be momentum that would remain constant and the velocity would decrease accordingly, causing the rock to harmlessly fall short*.

Who was right? Who the heck knows? They are describing a situation that is literally impossible in the real world, thus physics has no answer. Likewise the game designers never wrote rules for it.

The game designers did write rules for it. Look on page 9 of the 3E DMG, in the section called Adjudicating. The essential idea is that the DM must make a ruling, and then stick with it.

(In the transformation case, I would immediately remind both players that both momentum and velocity are only constant until acted upon by an outside force, which has just occurred. If they want to know what would happen, they can experiment. My ruling would be that the force it hits with is the force it's thrown with, regardless of velocity or momentum. Perhaps the rock changes slowly, just a little bit after it hits its target. It might work if thrown in a high arc, perhaps by a catapult, and had lots of time to change, and was also propelled by gravity after the transformation. But a straight throw hits with the force it was thrown with.)


I am not sure if it is reasonable to try and insist physics work a certain way in regards to an effect that is literally impossible. Take for example Teleport. If you used it to travel instantly from the pole to the equator you would, in the real world, be thrown to the ground and torn to pieces by the difference in rotational velocity. If the DM declared your PC dead as a result of that, would you say "Well, that's physics. Time to reroll,"? Or would you argue that the magical teleportation doesn't have any RAW or fluff mention of shredding people like that, and thus the spell must not work that way?

Once again, you are assuming the world is like Earth. It is not automatically a ball, nor is it automatically spinning, nor is momentum automatically conserved. My ruling in this case would be couched in modern physics language. You started out motionless measured by the obviously most reasonable frame of reference; you end up motionless measured by the obviously most reasonable frame of reference.


What if I said that the next time you cast a wall of force it stopped the planet dead in its tracks and caused an apocalypse? Because the wall of force says it is completely immobile and impenetrable, and it says nothing about taking a planet's orbital momentum (or indeed the momentum of the rest of the universe) into account.

What's a planet? What's an orbit? What's momentum?

If this spell has ever been cast before, then that effect obviously did not happen. It is immobile in the obvious frame of reference. Note the need to state a frame of reference. Once you assume modern physics, the word "immobile" has no meaning outside of some frame of reference. For instance, why are you worrying about the planet's spin, without considering the planet's path around the sun, the sun's orbit around the galaxy, and the galaxy's movement?


Its the kind of thinking that leads to the commoner rail gun, something that conveniently ignores some physics and some RAW, and then puts what is left together again in an exploitative fashion.

The commoner railgun is the perfect example of why you can't mix real physics with D&D rules. By RAW, maybe you can get 10,000 people to pass a spear in one round, but when it's finally used, it will do 1d6 damage. By physics, a spear that traveled that far in six seconds would do extreme damage, but 10,000 commoners can't make it happen. There is no set of assumptions under which this works.


IIRC the players cast an enlarged tenser's disk (I don't know if that is RAW legal, but as I said I use a homebrew metamagic system) to block a trapdoor and trap some enemies in a burning room while they sat safely below.

"The disk floats approximately three feet above the ground at all times. The disk also winks out if you ... try to take the disk more than three feet away from the surface beneath it." If the trap door is more than three feet off the ground, it doesn't work.

Also, As soon as over 100 pounds per level stand on the trap door, the spell fails. If they don't have that much weight, it might work.


While I appreciate the math, the spell never says whether that is the force required to break the disk or merely overtax its capacity for movement.

"It can hold 100 pounds per weight per caster level." It therefore cannot hold more than that. (And if it didn't say, then you would make the final ruling.)


*: A similar anecdote. I have a homebrew spell that instantly changes the facing of the target. The RAW use is to knock a standing person prone or vice versa, or allow a flying creature with poor maneuverability to execute an instant turn.
One of my players insisted on using the spell to turn an enemy's attacks around on them in midair. I said the spell doesn't work that way, and all it would do is cause the projectile to strike the same target blunt end first. The player insisted the spell MUST also redirect all momentum in the new direction, otherwise using it for an on the spot turn would be impossible, and using it on someone in motion would send them tumbling backwards as all their forward momentum is now going in the opposite direction.

DM: All right, Fred, your character believes that, and casts the spell. It doesn't work. George, it's your turn next. What does your character do?
Fred: But the spell MUST also redirect all momentum in the new direction, otherwise using it for an on the spot turn would be impossible...
DM: Fred, you're in combat. You tried it; it failed. If you spend more than six seconds assuming that it should have worked, then in the next round, your character will just stand there thinking it should have worked. George, it's your move.

Your problem has nothing to do with the application of physics, and everything to do with the fact that they don't accept that the DM controls the game.

NichG
2013-07-07, 05:42 AM
For the teleport case, the sci-fi equivalent is probably a really interesting problem. Consider a wormhole where the two mouths of the wormhole are on different points of a rotating object. What happens?

Generally speaking, the answer has to look something like 'when things pass through the wormhole mouths, a force is exerted on the frames containing the wormhole mouths that balances the momentum change between the reference frames'.

So one way to deal with it is that instead of worrying about Teleport, lets start with Gate and treat Teleport as a sort of invisible Gate. This says that when you use Gate, the frame containing the Gate should exert forces needed to balance momentum (and also energy, if you have a Gate that is going across a gravitational potential). The object crossing the Gate will basically 'feel' the transmission of momentum and energy as it goes, which might manifest as a sort of forcefield if you're going uphill or a tendency to be sucked through if you're going downhill. The momentum aspect is weirder, but I'd envision it being experienced as a kind of lopsided pressure or tug, like you might feel as a passenger in a car that's turning.

So now with teleport, just say that experientially you walk a short distance down a tunnel in the astral, where the length of the tunnel is set more by how long it has to be to safely smear out the effects of the change in energy and momentum between reference frames. So teleport actually takes slightly longer to go, say, 500ft up, than it does to go a few miles horizontally, because you need a longer 'tunnel' so that the caster can actually put in the uphill effort. If we assume that there is actual energy in the spell, the effort doesn't have to be the same as climbing a 500ft incline, and that goes a long way towards explaining weight limitations and range limitations and why they scale with CL.

Another way to look at it that is far more esoteric is that momentum and energy conservation exist as consequences of fundamental symmetries of physics with respect to translation in space and time. However, since teleportation goes through the Astral, in which space and time do not properly exist, those symmetries do not formally apply. This is kind of conceptually elegant, but it has really awful consequences if you play it out, namely that conservation of energy and momentum just don't work.

The reason thats awful is not 'the PC Wizard can blow stuff up'. Its that anywhere that connections to the Astral can form environmentally at some rate is gradually gaining or losing energy (since if its not conserved it will generally vary). If the rate of Astral connections is correlated to increasing energy, this effect will tend to self-amplify and basically the universe self-destructs due to its own fluctuations after some finite time. If they're correlated to low ambient energy then I think its stable, so there you can get away with it (but it defines a universal rest frame, etc, which is interesting but not too awkward really). If its decorrelated entirely you still blow up, but it takes much longer (rather than energy ~ e^t, its energy ~ sqrt(t)).

So basically in the second model, the fact that the universe exists implies that approaching ground-state energies is a way to create portals to the Astral. Which means, in quite elegant fashion, that if your PCs try to go to deep space they have a good chance of ending up on the Astral.

TuggyNE
2013-07-07, 06:45 AM
So basically in the second model, the fact that the universe exists implies that approaching ground-state energies is a way to create portals to the Astral. Which means, in quite elegant fashion, that if your PCs try to go to deep space they have a good chance of ending up on the Astral.

I can live with that. Not sure if catgirls can, though. :smallamused:

Kalirren
2013-07-07, 10:23 AM
So, I would like to ask a few questions about people's opinions on Force Fields and the physics behind them:

1: Does a force field behave like solid matter or does it behave more like a strong magnetic field that repels all matter?

I model a force field as a region of space of arbitrarily high potential, a perfectly mechanically reflective surface. Since mechanical force is just the negative derivative of potential with respect to distance, this should be able to give you any force field you like. I avoid tangling with magnetic fields this way. (EM fields have a vector potential component. Let's just not deal with that.)


1a: How much impact does running into a force field generate? Is it any? Does anyone know if you hurl a metal object into a strong enough magnetic field if the metal object will sustain structural damage from the impact or merely decelerate and stop dead?

Running into a force wall generates as much impact as running into a solid wall. Also, since sound is just a mechanical wave, a wall-shaped force field acts as a nearly perfect reflective surface for sound. No comment on the magnetic question.


2: Does a force field have friction?

Here, you have two choices. Think about the volume defined by the force field as having surface tension, or its surface having some sort of spring constant.

Now ask yourself a question. Is surface tension very high but finite, or is it infinite? Both are possible.

If surface tension is finite, then the surface is not frictionless. It is possible to create a frictional force on the force field by applying a force normal to the surface, causing the surface to deform slightly, and then changing the direction of that applied force while the surface is still deformed to get some transverse component to your motion. You'd essentially be making your own waves on the surface and then surfing on them to get anywhere, but any conversion of normal to transverse force is friction.

If however surface tension is infinite, then its shape is static, and possibly frictionless. (It could still have friction, if it were so designed.)


2a: Is it possible to climb a force field?

It is only possible to climb a force field (without chucking gear in the opposite direction) if its slope angle is less than the arctangent of its coefficient of friction. This leads immediately to the next result:


2b: If one is stuck on top of a horizontal force field can one push off it to escape or is one trapped?

If the forcefield has friction, you can eventually just crawl off. If the forcefield has no friction, start chucking gear in the opposite direction.


2c: Can a mobile force field be used to carry objects? Is there a weight limit?

This depends on how the forcefield is generated - mostly its shape.


3: Just how strong is a force field?

This depends on how the forcefield is generated. I would model the failure load of a force field as being proportional to its thickness and inversely proportional to its area.


3a: If hit with a huge force what will happen? Will it reflect the force entirely? Will it redirect into whatever the force field is anchored to? Will the force field move? Will the force field generator burn out?

This is very poorly worded. Forces act on masses and cause them to accelerate. They don't hit things. Impulses hit things. Since the force field is a perfectly mechanically reflective surface, any incoming impulse will be reflected at full strength (minus the work done against the surface tension of the field), though the effects this might have on any object would vary.

Since I don't like infinites, the way I prefer to model forcefields is with the very-high-surface tension model, along with a very high effective mass. Momentum from incoming impulses is conserved, but initially dissipated through surface tension. The generation mechanism is designed to damp the common harmonics of waves in the surface caused by surface tension. Eventually, in this way the work done by an incoming object upon the force field will be dissipated by the generation mechanism. The generation mechanism is programmed to fail in a controlled manner when the vibrations in the surface of the force field caused by successive impacts are too strong for the mechanism to maintain. This gives a force field finite hp, and makes them vulnerable to concentrated damage directed against its weakest point.

Wardog
2013-07-16, 07:22 PM
Some random thoughts and responses:

The "Laws of Science/Nature" are just our best description of the way things behave. If - in your game world - things behave in a manner inconsistent with the real world, then obviously the laws of science/nature are different. (I would dispute the claim that "magic overrrides the laws of nature" or "science doesn't work" - as long as it behaves consistently and predictably, [arcane] magic is just alternative-reality science).


Before asking any specific questions, the general answer is that science does not work in this world.
1. If a wizard can make a lightning bolt by the force of his mind, then energy is not conserved.
2. Any creation spell proves that matter is not conserved.
3. Flying dragons or stone gargoyles are proof that the cube-square law doesn't work.
4. Flight, Levitation or Feather Fall all prove that gravity is not constant.
5. Raise Dead, Resurrection, creation spells, etc. prove that entroy is not always increasing.

In short, the best answer to any such question is that the player is assuming constancy of laws that are provably not constant.
1) Unless he is drawing the energy from another dimension/his mana/the spell components/etc. (Why can a wizard only cast x spells per day? Presumably because his source of energy is limited).
2) Unless it involves energy-to-mass conversion (and 1), or summons matter from somewhere else.
3) Probably, unless they also have some inate levitating force...
4) Which doesn't necessarily mean that gravity itself is variable, just that magic is able to exert a force sufficient to counter gravity.
5) No more so that growing crystals/building a house of cards/ growing organisms does in the real world. Entropy can decrease locally - it just requires expenditure of energy, which causes more entropy elsewhere.




*: A similar anecdote. I have a homebrew spell that instantly changes the facing of the target. The RAW use is to knock a standing person prone or vice versa, or allow a flying creature with poor maneuverability to execute an instant turn.
One of my players insisted on using the spell to turn an enemy's attacks around on them in midair. I said the spell doesn't work that way, and all it would do is cause the projectile to strike the same target blunt end first. The player insisted the spell MUST also redirect all momentum in the new direction, otherwise using it for an on the spot turn would be impossible, and using it on someone in motion would send them tumbling backwards as all their forward momentum is now going in the opposite direction.


I don't see why it would behave like that. All the spell needs to do to have the intended effect is to apply a force or a torque to the target, to turn it round. If you did that to a moving object, it would (as you said) keep moving in the same direction it was going, but would now be pointing the other way. (Like a Babylon 5 Starfury spinning round to shoot "backwards" while maintaining its flight path).

And besides, if they can come up with a suitible real-world reson why it should do that, but you don't want it to, then as per my first point, and Jay R's comment, the laws of physics of the game world must accomodate everything that happens in that world. If your players (or their characters, assuming they have enough Int) want to spend time experimenting and analysing the behaviour of objects in the game so as to work out the game-world "laws of physics" (and how they differ from the real world), they can do so. But they can't use real-world physics to over-ride explicity-stated aspects of the game-world.

***

As for an example of "how force fields work", in the Polity novels, "hard fields" seem to obey laws of conservation of energy and momentum. If a shield absorbs too much energy (e.g. from laser hits), then the generatior will overheat or explode. If it suffers a sufficiently hard impact (e.g. space-ships colliding, or a hit from a near-c rail-gun) then the shield generator will be torn from it's mountings and sent flying backwards (most likely damaging the ship in the process). Warships often have multiple shield generators producing overlapping fields, so that when one becomes dangerously overloaded, it can be switched off before it is damaged, and a fresh field generated in its place.