Re: (TFT) Re: Demon slingshot

[Peter von Kleinsmid <pvk@oz.net>]

I haven't had time lately, but I'm catching up. Undead horses and others, 
beware.

(PvK yanks out his old physical Advanced Wizard book from his TFT bag for 
the first time this year, and flips to his home-made tab labelled 
"Gates  Magic Trade  Removing Magic Items"... he brushes up...)

> 1) Radius of planet measured by something like Eratosthenes' technique, 
> could be good to 1% or so (Eratosthenes was).

Ok, so it is possible someone could make a similar inference, even though 
most of the world world wouldn't even accept that the world was round for 
hundreds or thousands of years thereafter. But someone _might_ infer 
correctly, or get this info from Mnoren texts or just filtered down Mnoren 
information taken on faith thereafter, and confirmed by such observations.

> 2) Surface gravity measured by dropping stuff in a drop tower, probably 
> also good to around 1%.

Assuming one accepts and understands Newtonian physics, acceleration, and 
gravity - an advanced math talent not in ITL, ok.

> 3) Use Self-powered Flight or Carpet to go up to around 100km altitude. 
> Altitude verified by angular depression of apparent limb of planet (ie, 
> how far down is the horizon from straight level?). This also allows 
> incremental improvement of vacuum gear - go up until you turn blue, come 
> down, build a better vac-suit, try again.

Magic Carpets are stronger fliers than the Flight spell, but do you really 
think they beat, say, a 1910 biplane for performance?

Some real-world ceilings:
Jet fighter (F-15 absolute ceiling): ~30km
Jetliner (Boeing 747): ~14km
Very good WW2 fighter (P51): ~13km
Biplane (Spad): ~7km

I guess if we assume Magic Carpets use levitation or contragravity or 
something, then it would make sense they could float higher.

But then, how high is the atmosphere of your Cidri, and what do people have 
to do to stay alive up there, and does a magic carpet ever stop working at 
high altitude, or are you saying it'll do for a spaceship if you can only 
keep the passengers alive?

> 4) Hang a launch gate out over the North pole and build the facility.

Sounds like an amazing feat in itself, especially if Cidri is super-enormous.

> ...
> This still relies on having a good clock; I'm not sure exactly how to 
> solve this problem. Good pendulums are not bad, but you'll have to do 
> measurements down to sub-second values with good precision.

Not to mention mathematics. Modern aerospace teams have their work cut out 
for them doing this even with banks of computers and hundreds of engineers, 
etc.



> > However, if someone did begin this sort of experiment, and if it were
> > possible to specify gates that changed velocity or direction of velocity
> > while conserving amount of energy (which, I don't think is true),
>
> Agreed, and note that any gate that spans more than a few hundred km does 
> exactly this even for people just walking through it, if referred to an 
> inertial frame.

Ok, I'm re-appraising this having re-studied. The gate rules listed in AW 
are all about whether it will do what it does or not, not how it does what 
it does. The only parameters controlled by the wizard seem to be:

* Where is each side of the gate?
* What size is the gate (1 to 3 meters)?
* When should the gate transport someone/something, or not?

The two things the gate does are:

* Transport someone.
* Allow someone to step half-way to look through and possibly interact with 
something on the other side.

After considering I think it's implied that each side is the same size and 
shape, so it acts just like walking from one location to another.

Since there's no mention of needing to keep a consistent direction, it 
should be possible to make a gate that takes someone moving north, for 
example, and have them exit moving any other direction (although, it 
doesn't say anything about vertical gates... the assumption throughout the 
rules is that the movement is always horizontal).

Therefore, on re-reading and more reflection, it does seem to me like you 
should be able to re-direct kinetic energy with a gate.

I'm _not_ sure though, that it follows that vertical gates would be 
possible. It makes sense from a freefall perspective that they should, but 
on the other hand, who wants to say it should be possible to use the 7-Hex 
Wall spell to create a boulder in mid-air 3 meters over an opponent's head 
to flatten him with? Kind of a lame point, but still, something to consider.

Back to modern physics, gates that are vertical (i.e. perpendicular to a 
gravity field) have a constant and sustainable maintenance cost but an 
exponentially increasing energy yield (energy = mass x velocity x 
velocity), so it seems there is no conservation of energy, and in theory 
you could have a perpetual motion machine, or as much kinetic energy as 
you'd ever want (and more).

Here's a hypothesis:

Magic is accomplished by forces not included in modern physics, but they do 
seem to usually involve energy exchanges and some limits. The more powerful 
an effect, usually, the more energy required. So, inferring that we can get 
infinite energy from Gates seems inconsistent. The description says they 
allow people to walk from one place to another, not that they allow 
cataclysmic kinetic energy attacks. The energy that creates a gate sets up 
an unstable system that breaks down fairly often unless restabilized for 
half the energy needed to set it up. The costs to the wizard are flat, but 
perhaps it puts some strain on whatever system or energy field allows magic 
effects in the first place. Like stringing a rubber-band tensely between 
two pegs, suddenly you have a launcher that can launch many many paperclips 
across a classroom. Sometimes though, one or the other end of the rubber 
band may start to slip off, or the rubber band may need to be replaced. You 
could even pull it really far back and let something heavy fly through, but 
in that case you're going to stress the band even more and you'll get far 
fewer shots before the band breaks. So maybe Gates are like this. the 
description in AW covers the usual use, and maybe they do allow you to 
build up some good kinetic energy, but maybe only so much - exceed more 
than the kinetic energy of the usual maximum (say, 36 men running through 
per 5-second turn at speed 12), and perhaps the Gate will just snap and 
stop working, 50% (?) chance before or after transporting the last item. 
That would reduce the weapon potential to that of a nasty and especially 
versatile trebuchet, rather than a doomsday device (and also possibly one 
that backfires), at 100 fST, and wizard time, etc, per shot.

What the limit is, though, would be entirely GM discretion. GM could also 
of course say no limit, if they really like the idea. It could be what got 
the Mnoren to decide to leave.

There could also be other side-effects, like yes, you can get lots of 
energy, but it comes out of the local mana field, and you end up creating 
large low-mana or no-mana areas where magic doesn't work right, or at all. 
Maybe that's why the Wizard's guild leaves a few values out of the spell 
formula which also explains why the taught version only allows horizontal 
gates!


> Even Reverse Missiles will probably be ineffective against the shock wave 
> and UV  radiation, though it could be harsh on anybody around the exit end 
> of the targetting gate. (I assume the attackers would have sense enough 
> not to make the targetting gate 2-way.)

How about Control Missiles. ;-)


PvK
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