Spelljammer How do gravity planes work?

[jasper]

I don't need the tech details. But last night in the spelljammer Academy Realmspace adventure we were having trouble with what happens when you cross the plane? You are climbing down then suddenly what happens. For those who don't have the book. The ship is a ball with the gravity plane between the first and second deck.
Do you orbit a ship if you jump off? The Wotc Legends of Multiverse podcast has this happens alot.

 

[UngeheuerLich]

Do you orbit a ship if you jump off? The Wotc Legends of Multiverse podcast has this happens alot.

No. You oscilate.

This is the plane:

.......................................

You fall down, if you are above it and up if you are below it.

 

[DEFCON 1]

Boot up a game of Portal and a DM can set up all manner of scenarios of different gravity planes and such to see the results.

 

[overgeeked]

I don't need the tech details. But last night in the spelljammer Academy Realmspace adventure we were having trouble with what happens when you cross the plane? You are climbing down then suddenly what happens. For those who don't have the book. The ship is a ball with the gravity plane between the first and second deck.

Check out this image of the gravity plane. Wherever the gravity plane is that's the "down" for gravity. If you're above that line or below that line doesn't matter, gravity pulls you towards that plane. If you're climbing down towards that plane and reach that line, stopping say where your stomach is on that line, then gravity is pulling your head and feet towards your stomach. If you cross that line moving in the same direction you were going, you're now climbing up, away from the pull of gravity.

Do you orbit a ship if you jump off? The WotC Legends of Multiverse podcast has this happens a lot.

It depends. It's like skipping a rock. If you jump off you might shoot right out of the air bubble and find yourself in Wildspace or you might "skip the rock" (i.e. jump off at just the right angle) to circle the ship. Like you say, it's like orbiting something. All those precise calculations that NASA has to do to get something to orbit a larger object, yeah...your character has to run those numbers in their head and hope. It's a game experienced characters play. Throwing things off the deck at just the right angle to circle "under" the ship and either hit or be passed to a crewmember on the far side of the deck.

 

[Andras]

You drift outwards alongs the gravity plane at 10ft per round. if you exit the envelope you get left behind by the ship.

 

[EzekielRaiden]

No. You oscilate.

Bit late in reply here, but you'd likely also have damped oscillation due to the effects of air resistance, and possibly some weakening of the "restorative" force (what resists motion against the gravity plane) assuming the plane has some amount of thickness to it. So if you were (say) tied by a rope behind the ship, your position would oscillate and slowly decay to where your center of mass was located somewhere "inside" the gravity plane.

 

[kigmatzomat]

Orbiting won't happen with a gravity plane, it requires a gravity line or point where you could rotate around, like a gravity axle.

When you jump off, you will have a downward ( y ) and an outward (x) velocity component.

*--- x
| \
y z

The plane will cause the downward movement to oscillate across the plane, causing a bobbing motion vertically centered on the plane, slowed only by air resistance.

There is nothing impacting your outward motion, meaning you keep the same horizontal speed, slowed only by air resistance.

This will result in a sine-wave like movement as you move away from the ship.

\/\/\
..\/ \/

You could tie a rope to yourself and the ship, which could redirect the outward movement to simulate an orbit, but that would wrap you around the hull.

As there is no "breeze" in the bubble, it is possible for objects to simply lose all relative velocity and be stuck in at the plane some distance from the ship, but it would require a suitable low velocity.