[Runequest] Fact check

Asher Royce Yaffee ashersensei at gmail.com
Wed Mar 27 08:32:08 EST 2013


Hi, All,
   One thing to remember about a ringworld or spinning space station or
other such structure that gets "gravity" by rotation.  When you drop an
object inside the environment -- ring, station, what have you -- the object
does not continuously accelerate.  Ringworld's "gravity" is just about the
same as Earth's, in that we would be the same weight on Ringworld as we
would be on Earth.  But that is where the similarity ends.
   Let's say I paint a big X on the sidewalk, go up the elevator, and then
jump off a tall building in order to land on the X.
   On Earth, if I jump off a tall building, I would accelerate continuously
until either hitting the ground or hitting terminal velocity (due to air
resistance).  After one second, I would be falling at about 32 feet/second,
or 9.8 meters/second.  After 2 seconds, double my speed.  After 3 seconds,
triple my speed.  Etc.  The sidewalk below me would approach faster and
faster.  Barring strong wind, I can reasonably hope to land on or near the
X I painted.
   On the Ringworld, if I jump off a tall building, I fall at about 32
feet/second or 9.8 meters/second -- and that's it.  There is no further
acceleration due to gravity.  So I watch the sidewalk below approach at a
more leisurely pace.
   But there's more.  During my fall, I would observe the X slide out from
under me.  It would slide to spinward.  Very much like the case of long
ranged artillery, where the artillery crew have to compensate for the Earth
rotating underneath an artillery shell in its flight.
   For any normal jump -- out of trees onto foes, etc. -- on Ringworld, the
drift would be too small to notice.  But from 500 miles or 800 km up, it
would matter.  I would have to relearn how to do the math to figure out how
much the rotational velocity difference would be between the Ringworld
floor and the Ringworld rim to say how much it would matter.  Let's assume
that the troll has a strong enough parachute.  On the way down, the troll
would find that his landing zone is sliding away from him to spinward --
maybe by 60 mph.  Makes hitting a tree a whole lot more painful, too.
   Sincerely,
Asher
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