Rules:
*You can teleport into and out of it at will
*It has a couple of plug sockets and can connect to internet from the region you teleported in from
*You can take objects and people with you
*As already stated, it is (3m)^3 (3m*3m*3m). The walls are plain plaster with a light in the middle of the ceiling. The pocket dimension is topologically toroidal, so if there weren’t walls and a ceiling/floor (which you can actually destroy) you would loop if you went more than 3m in any direction. Gravity, then, is artificial and can be altered to anywhere from 0 to 2g from a dial on the wall.
Edit: additional specifications
*You can only teleport out to where you teleported in from.
*Time proceeds at the same rate inside the pocket dimension
*There is an eject button for those inside to get out if something happens to you
They wouldn’t go faster than terminal velocity if you keep air in the chamber, and even if you remove it, they won’t go faster than c. They’ll still go pretty fast, though.
I don’t think the drag force due to air would work the same in a system with such a high concentration of rocks. It’s not like one object falling through undisturbed fluid, which then has to get out of the way, in this case the air would gradually start to move along with the rocks.
This might be better modelled as turbulent flow of a mixed solid/air suspension. But there’s no ‘edges’ to the flow due to the looped dimension, so the viscous forces are pretty uniform… There would still be a terminal velocity, but much much higher than a rock falling through an atmosphere
Also I imagine the rocks would quickly grind themselves to very fine dust, once they pick up a bit of kinetic energy, so then it would behave more like a fluid with uniform density… Could it even end up as laminar flow?
Keeping the air was a mistake but I don’t see why it wouldn’t be able to go faster than c.