[Runequest] Fact check

strobus at sympatico.ca strobus at sympatico.ca
Wed Mar 27 08:50:09 EST 2013

Interesting stuff.
Question though - if the surface you jump from is moving at the same rotational speed as the ground, would your landing spot still slide out from under you, relatively speaking? The building you jump from would lend you some lateral momentum, no? But perhaps the top of the building, being closer to the axis, is moving slower than the bottom of the building. But then the air would also be moving, carrying it with you...
This stuff makes my head spin :-)
Makes me wonder how air currents and convection work in the ringworld, though.

Date: Tue, 26 Mar 2013 14:32:08 -0700
From: ashersensei at gmail.com
To: runequest at rpgreview.net
Subject: Re: [Runequest] Fact check

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.

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