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The Short question here is do teleportation spells in Pathfinder/3.5 carry over any kinetic momentum you were subject to before the teleportation. For context, please see this example situation (which will become a real situation depending on the answer):

Bob "This is a hypothetical situation" Hrothbert has just found himself pushed over a cliff. The cliff is high enough that he does not hit the ground after a single round, so is free-falling. Poor Bob did not prepare Feather Fall today, so he can't save himself that way, but he did prepare Dimension Door! Bob readies to cast this spell before he hits the ground, and just before he dimension doors himself to a nearby rock.

Does he A: Safely land on the rock, the kinetic energy having dissipated when he cast the Dimension Door spell

OR

Does he B: Take terminal velocity falling damage as he hits his new location just as fast as when he had teleported?

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8 Answers 8

Note that if you preserve momentum you get the Near-C rock issue with the spell.

The Near-C issue arises from the game Traveller where if you jump your velocity and vector are preserved. The problem comes if you accelerate a asteroid starship to near light speed and then jump to a target planet with the exit vector aligned to the planet. When the starship emerges a week later it will smash into the planet causing much damage possibly even causing it to crack if the starship's mass is large enough.

Because of it's velocity is near light speed there is virtually no time for any type of planetary defense to react. Even if it did the amount of energy in the starship would ensure even the smallest fragments would cause much damage.

Preserving momentum with Teleport (or Teleport Object) would cause similar problems in a Pathfinder game. Just drop a rock down a tall cliff or deep pit and then teleport it, while falling, above the chosen target.

So while the rules do not explicitly state which situation the interpretation I always used was that momentum is NOT preserved. Most referees I know interpret it the same way. The intent of the spell is as a means of transportation not as a method of attack so it is consistent to adjudicate the spell this way. The side effect is that you can teleport you or a target away from an impending high speed crash.

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+1 I like the traveler example. Though you couldn't actually use Teleport Object on a rock falling down a hole, it's a touch spell and you'd have to go with it. Though that'd be a pretty creative use of a 7th level spell. You could make it a Reach Spell which gets you up to 9th level spells, but then the damage is on par with a 9th level spell, so I'm not sure that'd be game breaking, since max range on a medium spell is....and I just answered my own question. –  Cthos May 31 '11 at 17:56
    
There is an old trap based upon a permanent dimension door... take a section of hall (usually 10'x10'), put the entry on the floor, and the exit directly above the entry (usually 10-15 feet up). Toss some rocks in, like a bucket full of gravel.... It works best if the upper chunk is an area carved out with, say, Transmute Rock to mud, so that it redirects the sideways momentum mostly back in. Anyway, each rock will do a rather nasty 10d6.... Lethal buckets of gravel. –  aramis Jun 2 '11 at 0:22
    
Teleporting a falling rock isn't going to work too well. Good luck aiming it just right. You probably just expended a high level spell in order to make a big thump and drop an obstacle on the battlefield. You also had to have someone sit out the battle in order to be in position to push the rock in the first place. –  Loren Pechtel Mar 7 '12 at 3:03
    
You can handle the Near-C issue in Pathfinder by saying that the instantaneous travel through the Astral plane has a terminal velocity of its own. You can justify this by saying that the Astral plane is not an infinitely large plane through which things travel instantaneously, but rather an infinitely small plane through which things travel at a set rate. This Astral plane terminal velocity could be relative to the object's drag, and therefore even if you go in at the speed of light, the Astral plane instantly absorbs all momentum above terminal velocity. You would still go splat, though. –  dlras2 Mar 7 '12 at 15:22
    
I have never played traveller, but I think as a gm in dnd I would be inclined to let a (reach version) teleport of a large rock work as a weapon. It would hardly be game breaking and it is creative. (Also, you don't necessarily need to stone to already have momentum as long as the target is such that it can't move, just teleport it high overhead, letting momentum be preserved just lets them teleport it to just overhead and reduce the chance to dodge.) –  TimothyAWiseman Jun 5 '12 at 22:27
up vote 49 down vote accepted

I should have been more thorough in my research.

The following comes from the Falling Section of d20pfsrd.com:

A character cannot cast a spell while falling, unless the fall is greater than 500 feet or the spell is an immediate action, such as feather fall. Casting a spell while falling requires a concentration check with a DC equal to 20 + the spell's level. Casting teleport or a similar spell while falling does not end your momentum, it just changes your location, meaning that you still take falling damage, even if you arrive atop a solid surface.

The emphasis is mine.

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Worth noting that as a game rule this works fine (irrespective of good "physics of magic" arguments either way). Teleporting is already a powerful, almost disruptive, ability, it doesn't really need the addition of conditional utility side-effects to still be a great spell choice. –  Neil Slater Dec 12 '13 at 10:30

Here's how I would rule this as a DM:

Dimension Door is classified as a teleportation effect. According to the rules on teleportation effects, they are "...instantaneous travel through the Astral Plane." The Astral plane has subjective directional gravity. This is where I would say that the spell bleeds the momentum from movement into.

Although normal subjective directional gravity requires the character to assign the "down" direction to slow and stop themselves, I would rule that teleportation effect spells would be designed to automatically assign the "down" direction to be the opposite of any existing momentum.

This would obviously bring up the possibility of someone researching a unique teleportation effect spell that does maintain momentum during the travel period.

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This is a good interpretation for 3.5. It would seem that 3.5 does not have the added bit that Pathfinder does, so it could possibly go either way in 3.5. –  Cthos May 31 '11 at 18:33

If Kinetic energy is not preserved by the teleport spell, then creatures in the process of moving when teleported should have to make balance checks or fall down. (watches character on flying dragon teleport above a volcano and fall to doom because all forward movement was halted) Since creatures do not have to make such checks, it follows that Kinetic energy must be preserved. :-)

P.S. Near-C issue is awesome... which is why planetary governments ought to create Dimensional Anchor interdiction zones to protect against the attack. Even more awesome would be a redirection spell that redirects incoming teleports into the Sun...

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For the Near-C teleportation issue, check out the comic: Schlock Mercneary. It covers this rather well. Relativistic Kill Vehicle –  Brian Ballsun-Stanton Mar 7 '12 at 13:40

Cthos answered it by the books but I'll throw out my approach as it's slightly different:

The problem with blindly carrying kinetic energy through a teleport is that you get nasty effects from planetary rotation. (The novel "The Witling" by Vernor Vinge deals with this quite well--long distance transit is via chains of lakes that are used as shock absorbers. The only intercontinental ports that are feasible are between like positions in the northern and southern hemispheres.)

Thus I rule that it's kinetic energy relative to your reference frame but you get some leeway in defining that reference frame.

If you're out in the open you get only one reference frame, the planet you are near. (If you're in deep space not near a planet then it's the star. For interstellar space it's the galaxy.)

Spaces that are contained give you the option of using either the containment or the environment of the containment (or even another step up if you have moving objects inside moving objects) as the reference velocity.

You're standing still and want to port to the ship at speed 10. If you arrive on deck you arrive at speed 10. If you port to a cabin you get to choose 0 or 10.

You're flying along at 20 and want to port to the same ship. Deck = 10 (assuming you're lined up right). Cabin = 10 or 20. Your friend pushes a wagon through the hold at speed 10 and you can arrive inside (assuming everything lines up) at 0, 10 or 20.

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Planetary motion? What's that? Everyone knows the gods created the firmament to be unchanged and unchanging. The sun rises in the east, sets in the west, and at night passes through the underworld, driving up the ghosts to harass the unrighteous. –  Alticamelus Mar 7 '12 at 9:12

Teleportation is an exercise in space time manipulation. Like all forms of space time travel it adheres to the rules of special relativity. Yes kinetic energy is conserved and yes it seems to change based on the perception of outside observers but this is not the case to person in transit in his relative case the gravity and directions have not changed at all. This is the natural skew and twist of space time caused by movement itself. Classic examples are the fact light spreads equal from a moving object from the perspective of the moving object the expansion is equal distant and even and the light does not appear to change. But from an outside observer it appears as if the light is warping and twisting (red shift and blue shift). Like wise in teleportation the teleporter does not feel any change in gravity, angular momentum and vector velocities while outside observers would percieve drastic changes in all of these factors. This inherent natural law of the universe would not need to any magic to compensate other then the instantaneous transport from one frame of referance to another.

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Nice interpretation. Do you have a source for it, or is it your own? –  Thanuir Jun 6 '12 at 4:03

Regardless of what the exact rules state I think that in general I have simply have the teleporting person, object etc, arrive with no kinetic energy relative to the location teleported to. It does allow a quickened teleport to save a falling person but eliminates a lot of other problems, like using a permanent to create infinite energy, and determining vectors upon arrival (teleported 3/4 or the way around the world) etc.

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Teleportation is usually tied to a destination location "I'm going to teleport to x square on (or above) the ground" or "I'm going to teleport on top of the roof of that moving steam train" etc. I've always thought the magic that anchors the destination matches the speed and velocity to whatever your destination is tied to.

I.E. if you teleport to 100 feet above the ground, when you arrive you're 'stopped' relative to the ground (immediately before you start falling). If you teleport onto an moving train, you're 'stopped' relative to the train. This seems to be more consistent when using teleport to arrive on/at moving objects. It's still open to abuse if used creatively, but to me this seems to be more internally consistent with the spell.

This would also mean if you declare a destination based on the original location ("I'm going to teleport 50 feet directly in front of myself") then I'd say your movement is preserved since your destination is relative to your starting position.

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