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Month Index: November, 1993


From:     bee@??????.??.??????.edu
Date:     Wed, 24 Nov 1993 18:30:09 -0500
Subject:  Re: Atmospheric Gravity Planes, speeds, etc...
 The whole argument sounds unneccesary to me.  The way the  
rules state that everything works sound just as sound as anyone  
else's physics-defiant ideas.  According to the way the rules explain  
it, the gravity  plane runs along a line, which is usually the  
longest and then second longest plane in the mass of a ship (which  
counts out the masts, wings, fins and so on, as they do not  
contribute any considerable amount to the mass of the ship.)  Because  
of this, the ship is weightless, as is has an equality of mass on  
both sides.  The reason the plane seems low in a ship (Making all but  
the lowest belowdecks areas gravity-down) is because of this balance  
of weight.
 A planet's gravity plane affects a ship in the same way as a  
larger ship or a decent-sized asteroid.  When two objects with  
gravity envelopes meet (that is, two objects with at least one plane  
of 25 feet or more I think...  it's a plane (keel length) that  
decides this) the object with the greater mass's "down" becomes down  
for both of them.
 The shift of gravitation occurs when the two gravity  
envelopes meet.  How do you know when this happens?  Simple: when the  
atmosphere envelopes come in contact.  The atmosphere and gravity  
envelopes occupy the same space and have the same surface.  Why?   
Again simple: the gravity envelope is what keeps the atmosphere  
envelope _in_.  Try this: touch a wet faucet with your fingertip.   
You can get really close, without getting wet, but as soon as you  
actually touch and the surface tension is broken, you get some water  
on your finger.  Now that your finger is wet, pull it away.  You have  
a "water envelope" on the tip of your finger.  If you touch the  
faucet again, the water on your finger and the water on the faucet  
merge again.
 Now, the atmospheric speed limit does not come from any  
limitations of the gravity plane or anything of the sort.  It comes  
from the fact that if you go any faster _through_ air, rather than  
carrying air, you will rip your ship to pieces.  But, alas, this is  
magic, so unless you encounter a storm or heavy winds, you can go a  
lot faster than your really could in the real world.  Reason?   
Because when a helm provides forward momentum, it does it for the  
ENTIRE SHIP.  Not just the hull, but everything down to the sails,  
the rigging, the fire in the galley, and the kender stowaway's  
topknot.
 Acceleration via spelljamming helm means no inertia for  
anything on board the ship.  But don't believe for a minute that when  
you jump overboard within an atmosphere that you won't be swept  
backwards (relative to the ship).  Not that I expect that anyone  
jumping overboard on a ship wold be thinking baout inertia anyway.
 And finally, for the flanaess or realms resident wondering  
why those jungle savages down by the equator don't fall sideways (or  
the ansalon resident wondering why the minotaurs UP by the equator  
don't fall sideways), another simple explanation.  Planets are ROUND,  
and in AD&D, apparently, evenly so (not pear shaped).  This makes the  
gravity plane attempt to expand all ways at once, and collaps in on  
itself, to a point at the center of the planet, thus making the  
center of the planet down no matter where you go on it.  On  
weird-shaped planets, presumably, gravity-plane systems are more of  
the norm, as on the rings of those planets that have them.
 Basically, what I am saying is that a ship's gravity plane is  
supposed to collapse AS SOON AS the atmosphere envelope of the ship  
and the atmosphere envelope of the planet touch.
 This works for all worlds with atmospheres (gaseous, that  
is).  For worlds without atmospheres, those who land on them are,  
forgive my elvish, fucked.  Basically, if you land a ship on one of  
those rare places with no atmosphere, the larger gravity plane  
_steals_ the atmosphere envelope, and everyone gets five melee rounds  
to scream (soundlessly) for divine intervention.  Or to cast the  
following spell:

 Maintain Atmosphere Envelope
 Mage Level 3, Priest level 2
 Mage: Alteration  Priest: Nature (air)
 Range: 0  Area Effect: 1 ship
 Components: S (hold breath)
 Duration: 1 hour per level of caster
 This spell allows the ship (or other vehicle) upon
 which the caster stands to maintain its own seperate
 atmosphere envelope (though not gravity envelope)
 from any it comes in contact with.  It also maintains
 the atmosphere when in contact with big things without
 one (like atmosphere-free planets).  It can be used 

 for cautious interaction with old-looking or undead 

 inhabited vessels, and can even be useful for submarine
 exploration (as it maintains a bubble of air around a 

 ship even in cases of landing on water)  The ship cannot
 land on water while the spell is in effect, but it can 

 land IN it.
  In the event that the GM uses this spell in a 

 non-spelljamming campaign, it is recommended that the 

 level of the spell become Mage 5, priest 4.



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Month Index: November, 1993

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