[Runequest] Fact check

Peter Maranci pmaranci at gmail.com
Mon May 6 10:14:24 EST 2013

Sorry to bring this up, but the issue is escalating and I could use some
insight from people who've actually parachuted. In the last session the
great troll had a couple of extra-large parachutes made, by a talented
tailor who had never been introduced to the concepts of parachutes before
(he's from a universe in which there is considerably less gravity than

The troll has never seen a parachute landing. His sole exposure to anyone
who HAD was a few seconds of grabbing a parachute off a WWII plane that was
under fire, and then a few seconds of combat while he killed the
paratrooper who was fighting to keep his parachute.

Here's the question: how hard it is to make your first parachute jump with
absolutely no training or experience? What would be some likely outcomes?

In this case, it wasn't a 500-mile jump to the Ringworld (that may happen
after the troll gets out of traction). It was a fall of about 800 feet, in
which a secondary parachute opened at about 100 feet up. He was wearing
full plate mail and carrying a greatsword and troll maul. According to my
reckoning, both of his legs are not only broken, but are effectively maimed
- although luckily for him, he's in the best hospital in a high-magic
world. Does anyone think that that's unreasonable? Because I suspect that
I'm going to get a lot of arguments on this one.

Also, do you think that his leg armor would survive the fall?


On Sun, Apr 7, 2013 at 1:09 PM, Styopa <styopa1 at gmail.com> wrote:

> All credit to Niven.  He's an intelligent fellow, and it's not casting any
> aspersions on him to simply say that the math behind a ringworld is
> extraordinarily complex, a nearly-unique frame of reference, and one could
> spend - especially in 1970, when Babbage's Children were barely toddlers -
> much of one's life down the rabbit-hole of computations trying to "get it
> right".  Personally, I'm much happier that Mr. Niven DIDN'T do so, and
> instead actually wrote the book, physics-warts and all.
> Frankly it's a fun exercise, and has provided some entertaining
> discussions between myself, and people who know more about physics than me
> - actual rocket scientists, some of them.  One (probably more usefully)
> spends most of his day working with the physics of golf balls.  (Well, I
> often do as well, but not to the MATHEMATICS of them.  Mine is a
> more....experimental...approach, using lots of profanity.)
> The fact is that (unless for some reason my posts didn't make it to these
> lists) I've proven with reasonable accuracy that our Armored Troll would
> fall the 500 miles in 406-some seconds (in a vacuum), and would hit at
> 000's of miles per hour.  Certainly, he'd hit terminal velocity before
> that, but he would MOST CERTAINLY impact with a most-terminal of velocities
> - probably several hundred miles per hour.
> Oh, and re the 'atmosphere' and 'spill walls' - yes, the point observed is
> accurate.  The height of the walls DIRECTLY impacts the atmospheric
> densities on the surface of the ring.  Assuming as physics-shorthand that
> the 1g force in the revolving frame of reference is uniform, the
> I'm NOT an atmospheric scientist, nor do I know any.  I'd speculate
> however that:
> - in this very odd frame of reference, I couldn't find any data on the
> surface cross section of liquids, but I *suspect* that it would be a
> shallow parabola, possibly a hyperbola.  But for this I'm just going to
> assume it's uniform in effect at the surface, because in any case I suspect
> a varying pressure effect laterally would anyway be homogenized by the air
> shifting around anyway.  For this model, assume the cross-section of the
> atmosphere height is horizontal (to someone on the ring-surface).
> - ANYWAY, I checked against atmospheric height and surface pressure for
> Venus, Mars, and Earth... just to see.  It turns out there's a fairly
> straight log-function that describes the relationship.  For Mars (atmos
> height ~25km) = surface pressure is 600 pascals.  Earth (~100km)
> 101kilopascals. Venus (~250km) 9 megapascals.  Assuming that the
> atmospheric behavior is the same when extrapolated linearly, a 500km-high
> side wall means probably 100 megapascals....or the pressure of water at
> 10000m depth (yes, 10km).
> The point of this atmospheric diversion?
> To illustrate only that the 500mile spillwalls DON'T necessarily mean it's
> atmosphere 'all the way up'.  In fact, given the quality of the Ringworld
> Engineers, it would make sense that they would OVER engineer the spillwalls
> to defend against pretty much anything that would 'cost' the structure
> airloss, if they could, so 500 mile sidewalls (800km) still still might
> only mean 100km atmosphere height.
> Simple enough...except for our trollish friend.
> Because this means that at least 7/8ths of his 'fall' from the edge (from
> the PoV of the surface), or of his fling-sideways (from the PoV of an
> outsider watching), is in vacuum....meaning he's going to 'hit' atmosphere
> at 000's of mph, relative.
> Taking into account the atmosphere, then, suggests that he would fall most
> of the way without atmospheric hindrance, until he hits atmosphere at
> something like Mach 7, and really doesn't enjoy the next few moments.
> On Sat, Apr 6, 2013 at 9:02 PM, Sven Lugar <vikingjarl at gmail.com> wrote:
>>  Ringworld is based on Larry Niven's book of the same name. I came to
>> know him fairly well back in the days when we both going to Cons & to
>> English Regency Dancing events. He always struck me as very stringent in
>> using his science in books. I remember an occasion of him discussing the
>> physics of it & also mentioning that it was based on the work of Dyson (of
>> the "Dyson Sphere concept"). So I suspect that he is probably correct in
>> his assumptions to make the concept work. Perhaps someone who is more
>> versed in these things can shed some light on this.
>> Sven
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Peter Maranci - pmaranci at gmail.com
Pete's RuneQuest & Roleplaying! http://www.runequest.org/rq.htm
The Diary of A Simple Man: http://bobquasit.livejournal.com/
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