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3D Sprinting
(title by Flying Toaster) "He's cleared the loop, now he's almost horizontal on the hairpin turn!" | |
I saw a video of somebody running a loop shaped track,
that's where he flipped a full 360 degrees and came out
the other end. If you're running fast enough, you can, for
a
second seem to defy gravity.
So take this concept a step further and have a running
track shaped like a roller coaster.
In addition to loops,
you'd have sharp banks where the runner would be
almost
horizontal.
If you weren't going fast enough, you'd simply fall off the
track.
This would be a no brainer great addition to those
obstacle
course shows that are pretty popular these days.
And if the ratings drop? Put the whole thing over an
alligator pit for the next season.
And kudos to Bigsleep even though his anno makes no
sense any more since the title change.
Runner doing a loop de loop.
https://www.youtube...watch?v=OTcdutIcEJ4
Fast forward to 2:20 [doctorremulac3, Aug 12 2015]
Discussion of some non-traditional racing
http://coloradoobst...acle-course-racing/
[scad mientist, Aug 13 2015]
The easy way with roller skates.
https://www.youtube...watch?v=kBo0Tsv5v0s
Of course a running course would need tighter curves. [doctorremulac3, Aug 13 2015]
[link]
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And jumps; with the approach and landing ramps angled for an appropriate approach speed, you should be able to clear an impressive distance. |
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The problem is that the animal stride is not well
equipped for running on non-horizontal surfaces. Every
instance I've seen of a runner "looping" is essentially a
running backflip inside the loop. |
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The reason is that the human stride consists of about 90%
upward push and about 10% forward push (numbers
pulled out of the air, but it's something like that). A
runner in a forward leaning sprint can do significantly
better, but still not great. This works fine if you've got a
force (gravity) countering that upward push, but not so
good if you don't. Since so much more of the force is
upward than forward, the human cannot physically run
fast enough to treat a banked surface as a straight one
for any significant degree of bank for any significant
length of time. |
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//the human cannot physically run fast enough to treat a
banked surface as a straight one for any significant
degree of bank for any significant length of time.// |
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Who said anything about "significant length of time"? Ever
seen anybody do parkour off of a wall? You run up to it,
run on the wall horizontally for about 2 seconds then
obviously return to the vertical. |
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As far as your incorrect contention that a runner is just
doing a backflip when he runs a loop de loop, see link. |
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I stand by my statement. He's dependent on the push off
the far wall to make contact with the near, he never
actually takes a step along the wall as such. |
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Except that he does. Watch the video. |
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" numbers pulled out of the air, but it's something like that " |
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So what are you saying, you can't have a course that
features the loop for starters and has less challenging parts
based on the loop as well such as a sharp hairpin turn where
he doesn't go fully inverted but merely goes horizontal for a
second? |
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Simple loops are for wimps. What's needed is a
runners' wall of death. |
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//Except that he does. Watch the video.// |
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I did. One foot on the front wall, countering his forward
momentum. One foot on the top, countering the upward
momentum. One foot on the back wall, countering the
push off the front. Landing. And he has to catch himself
from falling on the landing. He's not running around the
loop, he's using the loop to control a flip off the front
ramp. |
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Once again, what I mean very specifically, is that unlike a
rolling vehicle, his speed is not, and cannot be, sufficient
to hold him to the loop. |
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//Hold him in the loop//? What on Earth are you talking
about? |
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The guy ran through a loop. Idea is for a track that
features these loops and simpler, less hard to traverse
versions of this loop such as horizontal hairpin turns
similar to a roller coaster. Traversing these hairpin turns
would be similar to a parkour runner running up and
down a vertical wall. They would not be "held in the loop"
or remain horizontal for any "significant length of time"
so I'm not sure why you keep referring to these concepts. |
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If you're still not getting it, I don't know what to tell you. |
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//his speed is not, and cannot be, sufficient to
hold him to the loop.// |
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I agree with [MechE]'s analysis of the video, but to
be honest that's not the point. The guy did
effectively run around the loop. The forces he was
applying were broadly similar in type to the forces
he'd be applying if he ran level, but not quite.
There is an element of back-flippiness to it. |
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The real test would be whether he could complete
two or more loops - sustained looping. I'm not
convinced that he couldn't. |
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The other relevant question is: what speed would
the runner need in order to maintain, say, 1.5G of
centrifugal force? (Why 1.5 and not 1? Because 1G
would leave him with net zero G at the top of the
loop, and he wouldn't get any traction. With 1.5G
centrifugal, he has 0.5G of force between him and
the top of the loop, which is enough to maintain
traction.) |
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Well, let's assume that the loop is 3m in diameter
(1.5m radius), which seems a reasonable minimum.
Assume also that the runner's centre of mass is 1m
from his feet (that's not quite right, but it will do).
So the radius around which his centre of mass goes
is 0.5m. |
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It turns out that a speed of about 5.5m/s, or
around 12mph, will be enough to provide 1.5G of
centrifugal force. Of course, he's doing some of
that vertically, which will be strenuous, but it's not
insanely impossible. |
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Right. Not insanely impossible, but insanely difficult,
which is
the point. |
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However you break down what is happening to get him
through this loop, or through a near horizontal hairpin
turn,
you'd have to have a certain amount of speed and
momentum to get you through the obstacles. Too slow,
you fall off the track. |
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Let's face it, running isn't all that exciting to watch, or to
do for that matter. With this roller coaster track, if you
don't run fast enough, you plummet off the track. In the
case of the loop, you fall directly on your head,
something that seldom happens in regular running races. |
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All the aspects of a roller could be featured, including a
sharp drop. If you've ever ran down a hill that's sharply
angled down, you'll know that simply keeping on your feet
is pretty hard to do. You've got to get going really fast to
"catch a continuous fall" basically. |
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I'm seeing a lack of buns for this. Did I mention this would
be much more dangerous than regular running tracks? |
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[+] the vid of somebody actually doing it clinched it. |
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In that video I noticed that the guy's head was almost
stationary. I think that was a large contributor to why it
looks somewhat like a back flip. Of course making the
radius more than the runner's height is going to make the
required speed higher. |
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Regarding the 1.5G recommendation: Like you said, that
means that at the top of the loop there's 0.5G (great),
but at the bottom there is 2.5G. When's the last time
you tried to run carrying a pack that's 1.5 times your
weight? |
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Also check your calculations, it looks like (5m/s)^2/1.5G
= (25m^2/s^2)/(14.7m/s^2) = radius of 1.7m, not 0.5m
like you said. |
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One solution to lower the Gs at the bottom of the loop
might be a non-circular loop with a tighter radius at the
top and gentler ramps into and out of the loop. |
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Another option might be a loop with a radius of about 2.5
meters with a gymnastics bar (or similar) through the
center of the loop. The runner would reach up and grab
the bar as they enter the loop. This would allow them to
more efficiently swing their weight up and around rather
than requiring all the centripetal acceleration to come
from their legs. It would of course also allow doing the
loop with less than 1G. It looks like raising the center of
mass 3 m in this case will use up 5.4m/s of the original
velocity, but assuming a reasonable athlete can manage
7 or maybe 8 m/s entering the loop, they should have no
problem getting over the top. I'm not sure if they could
maintain enough speed to avoid negative Gs a the top, so
that may rule out a trapeze for larger diameter loops. |
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Of course the race course should include several different
types of loops of various size/shape. |
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Added link to some info on similar-ish racing types.
Parkour looks fun, but that tends to not focus on timed
racing. I can see why since there could probably be a lot
of injuries on concrete obstacles if the focus was on
speed rather than form. I could see a race like this idea
as having a niche if the obstacles are designed to in
general become less dangerous at higher speeds. A wipe-
out would generally result in sliding off the track into the
pads (or alligator pit). On a well designed endurance
course I could see a that a winning strategy would involve
pacing yourself on the less technical sections so that you
had enough energy left for the final loop or 90 deg
hairpin turn. |
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//result in sliding off the track into the pads (or alligator
pit)// |
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That would depend on how high you wanted your TV
ratings. |
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You know, another daunting obstacle would be a simple
ramp at the and of a steep slope. Picture the track going
down and then turning up into a 90 degree angle relative
to the ramp. You hit
that too softly you're essentially running full speed into a
wall.
You'll have to run like heck to keep perpendicular to the
track as it angles up or Blammo! |
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I'm not capitalizing "blammo" to give it proper noun
status, but to more accurately represent the sound you'd
make hitting the ramp turned wall. All caps would be too
much, hinting at a sustained booming sound where it
would actually be more of a sharp attack followed by not
much else, indicated by the capital B and followed by the
lower case "lammo", perhaps representing bouncing,
flailing limbs and such. |
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I think the onomatopoeic word would be "Blap". |
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"Bla-blap" perhaps if there was a bounce invloved. "Blap"
implies a more gruesome outcome. |
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Anyway, see link for a guy doing it the easy way with roller
skates. The running course would need tighter curves of
course unless the guy could run 40 miles per hour. |
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If there's a bounce, the sound is more
"nuAAABlap...tmp." |
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There's probably a voice-to-text algorithm that could be
tweaked to give you pretty good onomatopoeic (my new
word for the day) words. Just hold the mic up to the event
and have it read out an approximation of how you'd spell it. |
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Might help answer age old questions like "How do you spell a
raspberry?" |
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My problem is that you are describing it like a
roller coaster track, and it doesn't work. You can
do a backflip. You cannot run around a loop larger
than the backflip you can do. |
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You can do one or two steps up against a wall for
your hairpin turn and then drop down to the
ground underneath it. You cannot make a banked
turn like a wheeled vehicle and end up upright on
the same track you
were running before. So everyone "falls off" the
track, at most the challenge is can you start with
enough horizontal momentum to reach the next
platform. |
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As a parkour course, sure. As a roller coaster like
track, no. |
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//what speed would the runner need in order to
maintain, say, 1.5G of centrifugal force?// |
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They can't. That's my point. A wheeled vehicle
gets its forward momentum entirely through
friction tangential to the wheel along the
supporting surface. The normal force (that extra
0.5g) is required for friction to happen, but the
component imparting motion is entirely tangential
to the surface. |
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A running individual gets its forward momentum by
pushing down and back sufficiently to overcome
gravity. The force imparting motion has a
tangential and perpendicular component. By
definition, if they impart motion in the direction
of travel, they are also imparting sufficient motion
towards the center of the loop to overcome the
inertial forces holding them against the loop, and
they will lose contact with the loop without being
able to make an additional stride in that direction.
In the case of the video, he never makes an
additional stride in that direction, he instead
pushes off of the wall in each direction once,
which is what gives it that element of
backflipiness, because it was. |
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Big, you're absolutely right. Just running down a hill,
while one might think would be easy since it's going
down, is about the hardest thing you can do on your
feet and when you hit that upturn, you've got some
challenges. |
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Just keeping upright overcoming the gravity and
momentum pulling you down is hard enough, but
when you slam into an upturn, well, do the math on
that. I weigh 180+ pounds, I'm running downhill at
around 20 miles per hour at least since I'm making
huge strides and basically engaging in a controlled
fall. Then I'm supposed to re-direct all that mass
almost 90 degrees? How many pounds are my legs
supposed to support for that split second? That
sounds like a sporting event to me. |
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//My problem is that you are describing it like a
roller coaster track, and it doesn't work.// |
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Mech, I'm pretty sure that's not your problem. I've
described a track featuring a loop shown in a video
that shows a guy traversing it, you say he can't
traverse it, yes, he can, it's on video. I really don't
know what to tell you. Just bone it and move on my
friend. Let it go already. |
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By the way, speaking of running down hill, many
years ago I had the genius idea of running down the
side of a very large hill and when I lost it, made the
bad decision to not just sit on my butt and slide the
rest of the way. I kept on my feet and basically
jackhammered every bone in my body. Messed up my
hip socket and needed to walk on crutches for a
couple of months. Somehow it completely got better,
socket injuries can tend to be permanent, but I
learned my lesson. |
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Perhaps the video is fake. CGI track, rotary camera mount, convincing acting. |
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I did not say he cannot traverse that loop. I said he cannot
run around that loop. They are two different things. |
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And a backflip is around your center of gravity taking into
account your momentum. If you do it from a running,
jumping start, it goes forward and up then back down as
gravity dictates. That is what he is doing, but he's using
pushes off the wall to control that momentum. He is not
being supported by the wall the same way a vehicle in a
loop is. |
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I'm with MechE - I've watched the video, and in the slow motion replay it's clear that the foot plant at the top of the loop is very gentle, and he's basically coasting at that point.
Don't get me wrong, I think it's valid to claim it as a loop-de-loop - but the point is that you can't extend from that to a 'wall of death'. Because humans can't run all that fast, and don't have much in the way of down-force. |
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However this went past unanswered: |
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//So what are you saying, you can't have a course that features the loop for starters and has less challenging parts based on the loop as well such as a sharp hairpin turn where he doesn't go fully inverted but merely goes horizontal for a second?// |
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And I think the answer is that you could. |
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But.
Let's go back a moment. |
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//the human cannot physically run fast enough to treat a banked surface as a straight one for any significant degree of bank for any significant length of time.// |
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Humans just don't have the downforce. Until...
we attach the rocket powered 'spoilers'! |
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//you can't extend from that to a 'wall of death'.
Because humans can't run all that fast, and don't
have much in the way of down-force.// |
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A simple calculation of centrifugal forces shows that
an athletic human should be able to run around a
fairly small vertical wall of death. It would actually
be a lot easier than doing a loop, since they don't
have to suddenly raise their centre of mass. |
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// simple calculation of centrifugal forces shows that an
athletic human should be able to run around a fairly
small vertical wall of death.// |
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But you can't model a running human that way. Running
is not continuous contact with the ground, it is a series of
pulses pushing off the ground. As a result you have a
mixture of extreme centripetal acceleration and none, as
opposed to the average centripetal acceleration found
when a wheeled vehicle attempts the stunt. |
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// A simple calculation of centrifugal forces shows that
an athletic human should be able to run around a fairly
small vertical wall of death. // Can you show that
calculation? |
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You'll need to make an assumption about what angle is
possible. From personal experience I can pretty easily
walk on a 4:12 (rise:run) pitched roof, and would
probably have little trouble running crosswise on such a
slope. On a 9:12 roof, it would be highly questionable.
But lets say the surface was really gripping and somehow
I could run without twisting my ankle. That requires
12/9 = 1.3G of centripetal force. That plus the force of
gravity = sqrt (1.3^2 + 1) = 1.67G. (like running with a
pack containing 2/3 your body weight on a surface
sloping 37 degrees to the side. That's maybe on the edge
of possible. |
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To get 1.3G centripetal force, you could maybe be
moving your center of mass at 4m/s in a radius of 1.2m.
Assuming your feet are 1m below center of mass, they
will be travelling 4ms*2.2/1.2 = 7.3m/s. |
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So it may be possible to run on a vertical wall of depth
with a radius somewhere around 2.2m. Okay, so I did the
calculations myself. |
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// But you can't model a running human that way. // |
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I don't see why not. A normal runner running on a flat
surface is fighting gravity using a series of pulses. When
running around a curve, they are fighting gravity plus
inertia with a series of pulses. If you calculate the total
acceleration, it becomes equivalent to running on a
planet with stronger gravity or running while carrying a
heavy load. That of course severely limits what is
possible. With a wheeled vehicle it's easy to handle
several Gs without seriously changing horsepower
requirements whereas with running the upper G limit will
be small and the runner will tire very quickly near that
limit. |
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//you have a mixture of extreme centripetal
acceleration and none// |
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When you run, you are only applying a force
against G while your foot is in contact with the
ground. |
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I'll grant you, running around a wall of death will
be very demanding. But I don't see it as
impossible. |
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As a reductio ad absurdam, suppose we give a
motorbike solid tyres. Clearly, it can still do the
wall of death. Now we cut cross-wise grooves in
the tyres, so that maybe 20% of the rim is missing
(split over say 12 segments). The ride will be
bumpy, and the rider may have to steer "up" a
little to compensate for short intervals of
griplessness, but I think it's still doable. |
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So now we make the gaps in the tyre less
numerous (and wider). I suspect that, if the rider
could take the bumpiness, we could approach a
situation roughly equivalent to human footsteps. |
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Or, if you prefer, consider the trajectory of the
runner while both feet are off the surface. He will
start to drop in a half-parabola which lies in a
plane tangential to the wall at that point. Since
he is moving forward, he will continue to move
closer to the in-curving wall as he falls, allowing
him to place his next foot. |
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And to compensate for the dropping between
footfalls, he just has to run "uphill" somewhat. By
doing this, he ensures that while his feet are off
the walls, he will describe a full parabola (ie,
upward and then downward); if he gets it right, his
next footfall will happen when he has returned to
his original height. |
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A running wall-of-death is definitely possible.
Whether it exceeds the athletic ability of a fit
human I am not sure, but I doubt it. |
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Back in the 80s before we covered it up
permanently, we had a pool which featured a
circular, sloping deep end that was roughly conical.
The bank was about 45 degrees, and we enjoyed
running circles around it as kids. It might have been
about 9 feet deep at the bottom and thus about 18
feet in diameter. We leaned in maybe 25 degrees or
so. Centripetal force is cool as a kid. |
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That gives me another idea. |
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Ladies and gentlemen, we have a last minute title change. |
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(Credit will be given where due) |
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We can't give any more credit for this idea but we're willing
to say something nice about you at the end of the idea. |
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[bigs], I'm really sorry. My condolences.
Paul. |
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Holy shit. Big, I'm so sorry. |
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