"Gravity" on the Station

by Thorfinn

19 January, 1997


<warning mode=Physics by non expert>

The spinning motion of bab5 does *not* generate gravity. It generates the *illusion* of gravity, by providing an "apparent" down force towards the outer walls of the station.

The best explanation of how gravity works involves rubber sheets and balls... Umm... Well, I'll go ahead and explain it anyway. :) It isn't kinky, honest. *grin*

Okay, if you view space/time as a rubber sheet (two dimensional, to simplify the look of the thing), all objects sit on this rubber sheet, and make dents in it.

The more *mass* an object has, the more of a dent it makes in the sheet.

Now, if you as a little tiny ball bearing, go rolling past the earth (make it a soccerball filled with umm... neutronium, which is horribly heavy), you slip into the dent in the rubber sheet, and get sucked into it.

That's gravity. Bab5, despite being 5 miles long, isn't going to make much more than... a little pea sized dent in the rubber sheet, so not much gravity is created.

Now, as for what *appears* to be gravity... that's not gravity at all.

As Newton said in fancier language, "things want to travel in straight lines".

This means that, when you have the station in cross section: 

direction
of spin
 <-- __
       \
centre  \
   |     |
   V     |
   o-----| <- outer hull, 
         |   call this specific
         |   location point H
        /

Okay, lets label the axes of direction too, so we don't get confused... 

Y-axis
   ^
   |
   |
   |
   o---->X-axis
  /
 /
/
Z-axis, poking out 
from the screen. :)

Now, the station is spinning around the central section (along the Z-axis), right?

Okay, now, say you're holding on to the outside of the hull at point H, presumably in a space suit, otherwise we wouldn't be discussing this. ;)

You let go... what direction are you going to go?

You get sent flying off up along the Y axis, in a straight line...

Now, say you're standing on the *inside* of the hull.

You still want to go flying off up along the Y-axis, except that you *can't*, because the hull is holding you up.

This means, that the hull has to exert a force <--- along the X axis, to keep you from breaking through it, so you *feel* like you're being pulled "down" ---> along the X axis towards the "floor".

Urm. I'm not sure how clear that was. Hopefully it was okay. :)

Apparently some interesting effects occur when you pour liquids and so forth, because, of course, the liquid pours "sideways" somewhat... This is unfortunately an effect that is difficult to reproduce in a real gravity field, so we probably won't see it on camera. :)

Any real physics geeks are free to correct my analogies, but I think they're pretty good.

Basically, rotation makes an illusion of gravity, not real gravity. If you wander into the centre of the station, you will *not* get sucked out towards the hull.

</warning>


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This page is maintained by Alys and was last updated on 21 February, 1997. 1