# Re: Moon trials

Discussion in 'rec.sport.unicycling' started by Evan Byrne, Apr 10, 2005.

1. ### U-Turn Guest

ObieOne's argument is only correct for short hops. In a hop, you are
pushing up your center of mass. Tucking changes your shape so that
your feet are closer to your center of mass. This tuck-distance is
fixed by your body length and tuck skill, and does not change in the
decreased gravity. However, your center of mass's hop height does change
significantly when you are on the moon. So the 75% (the tuck's
contribution to the overall hop height) drops way down.

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2. ### burnitalltwice Guest

well concerning the black tire/heat problem theres always the primo the
wall tire in white which would reflect the heat. If this stuff is at all
possible the unispin will look like childs play. Tricks would turn into
bmx like spins and flips it would be about who ken get the most combos
in. Instead of landing tricks people would be worried about finding more
ways to stay up and add to combos of tricks that would be nutz. It would
be kinda like riding on a non flexing trampoline with superbly strong
legs. Of course all of this would prolly not be possible wearing normal
space suits. It would probubly have to be indoors some how but that also
might cancel out the null gravity effect, and also the frame of the uni
would have to either be assembled on the moon (hard because no fire) or
be made so that there are no completely sealed portions of the frame so
that little portions of earths atmosphere were not taken with it because
then wouldnt the frame explode because of the release of pressure. the
tire would have to be made very forgiving so that it can expand and
shrink to adjust to the atmosphere. but all in all that would be crazy
if at all possible.

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3. ### johnfoss Guest

burnitalltwice wrote:
> *Instead of landing tricks people would be worried about finding more
> ways to stay up and add to combos of tricks that would be nutz. *

I can picture Julien Monny (in the gym of course; he never wears a
shirt) doing handstand coasting, with his hands on the front and back of
the seat.

> *It would probubly have to be indoors some how but that also might
> cancel out the null gravity effect, and also the frame of the uni
> would have to either be assembled on the moon (hard because no fire) *

If we build a gym on the moon, we'll bring some fire along. But there's
no reason the vast majority of Earth unicycles will have a problem on
the Moon except for being over-built. I only have one I'm aware of where
the frame seals air in. On that one, if necessary, I could drill a
little hole.

Meanwhile, building a gym doe not affect your gravity unless you put it
in orbit. That's another unicycling story entirely.

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4. ### PhilS Guest

> Having legs with 6x normal power, one would not have to extend his
> legs as much before landing;

actually, you would still hit the ground with the same force as on
earth, seeing as you are 6x as high and 6x as fast.

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UNICYCLE UNICYL UNICYC UNICY UNIC UNI UN U UNICYCL UNICYC UNICY UNIC UNI
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5. ### Naomi Guest

"maestro8" <[email protected]> wrote in
message news:[email protected]
>
>
> Consider also that your unicycle will weigh 1/6th of what it did on
> earth... so when you do your massive moon hop, and you pull up on your
> uni as hard as you would on earth, it will accelerate towards your
> crotch 6x faster. Ouch! I hope that was a seat-out hop
>

Nope: force =mass x acceleration. not weight times acceleration:
it WILL accelerate towards your crotch faster (not 6x faster) , but only
because it is gaining less potential energy, leaving more of the energy you
supply to accelerate the uni. and increase its kinetic energy ( the bit
that hurts) .

6. ### Naomi Guest

"TheObieOne3226" <[email protected]>
wrote in message
news:[email protected].
>
>
>
> You wouldn't be able to hop 12 feet. 75% of hopping hieght is determined
> by how much you pull the unicycle up, which isn't changed much by the
> decreased gravity.
>
>

Agreed! 3 or 4 feet might be a better guess for vertical hop

Nao

7. ### Naomi Guest

"gerblefranklin" <[email protected]>
wrote in message
news:[email protected].
>
> Evan Byrne wrote:
>> *i thought it was 2% of earths gravity *

>
>
> Nope. Something missing from you understanding is that the force of
> gravity followsx the inverse square law. This means that if gravity
> pulls me with 40 lbs* from 10' from the edge of a round mass, it will
> pull with 10lbs from 20's away.

On the right lines but the distance is from the centre of gravity, not
from the edge of a round mass :-0

Yes me again!!!! Nao ;-)

8. ### gerblefranklin Guest

Naomi wrote:
> *"gerblefranklin"
> <[email protected]>
> wrote in message
> news:[email protected].
> >
> > Evan Byrne wrote:
> >> *i thought it was 2% of earths gravity *

> >
> >
> > Nope. Something missing from you understanding is that the force

> of
> > gravity followsx the inverse square law. This means that if

> gravity
> > pulls me with 40 lbs* from 10' from the edge of a round mass, it

> will
> > pull with 10lbs from 20's away.

>
> On the right lines but the distance is from the centre of gravity,
> not
> from the edge of a round mass :-0
>
> Yes me again!!!! Nao ;-) *

No, not you again (well, we're both right, in a way...). Close, but
no. There's a reason why Newton waited 20 years to publish his papers on
gravity, even though he already had the equations figured out. The issue
at hand was that in his papers he had simplified Earth's mass to a point
source. He waited to verify if this was okay, and that 20 year interval
was spent inventing integral calculus so that he could check it.

You can't reduce all shapes of mass to a point source, so you are also
wrong, in a way (yes, i was completely wrong on that one, but lets
assume i was talking about doing sidehops off of small singularities, in
which the center of mass is also the edge. We will ignore the infinitely
blueshifted gamma radiation and extreme tidal forces). You can't
simplify a barbell to a point source of gravity, even if you know the
center of gravity. So we were both off.

As for 3 or 4 feet, i don't see why we need to go to the moon for that.
Zack B and Ryan A are already at 3.5', and riders as weak as me are
approaching 3'.

--
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9. ### Naomi Guest

"gerblefranklin" <[email protected]>
wrote in message
news:[email protected].
>
> I don't see how the physics don't work out. Low gravity +
> disproportionatly strong legs + low mass= gigantic hops, easy trials.
> Precision might suffer a bit, but who cares? It's not like there's rail
> gaps on the moon.
>

So many misconceptions and errors in this thread. I tried to resist the
temptation to ignore them all, but have failed, so I will just pick a
couple at random. Sorry gerblefranklin, but the random finger hit you
first: And it will all probably help a few students with their coming
GCSE's so I am going for it. ;-)

Mass is unaffected by being moved to the moon, You meant low weight of
course. I am sure you did.

Nao

10. ### Naomi Guest

"gerblefranklin" <[email protected]>
wrote in message
news:[email protected].
>
> No, not you again (well, we're both right, in a way...). Close, but
> no. There's a reason why Newton waited 20 years to publish his papers on
> gravity, even though he already had the equations figured out. The issue
> at hand was that in his papers he had simplified Earth's mass to a point
> source. He waited to verify if this was okay, and that 20 year interval
> was spent inventing integral calculus so that he could check it.
>
> You can't reduce all shapes of mass to a point source, so you are also
> wrong, in a way (yes, i was completely wrong on that one, but lets

Of course you cannot actually reduce shapes to a point source, I don't
think I said that, but for a (1) uniform density object ( a simplification
I did make) using the C of G point works for the calculation of gravity (
and weight) at a defined distance. Calculus can fairly easily prove this.
Newton may not have been able to initially prove it, but he was still
correct. Certainly you cannot use the surface of the object from which to
measure distance, or else at 20 feet above the earth we would have only 1/4
the weight we have at 10 feet above it. bathroom scales would require
calibration based on their height and you would weigh noticeably less stood
on tiptoe. But you know all this of course.
The problems of reducing a mass to a point source come once you start to
rotate that object, at which time the mass distribution ( shape and size)
becomes highly important
(1) in the earth, local accumulations of heavy , or light ,rock do have a
small effect on local values ( and direction ) of g, because the earth is a
lump of material having a variable density. Such variation is, however,
quite small.

> As for 3 or 4 feet, i don't see why we need to go to the moon for that.
> Zack B and Ryan A are already at 3.5', and riders as weak as me are
> approaching 3'.
>

I didn't know people were up to 3.5 feet, I thought it was only around a
couple, but the question remains, as another posrter pointed out: How
much of that height is gained by lifting the uni up under you? That
distance will not change by a factor of 6. There is no way you can multiply
that 3.5 feet by 6 on the moon, because much of it is gained by another
means than just the energy used in jumping. It is gained by

Nao

11. ### maestro8 Guest

Naomi wrote:
> *Nope: force =mass x acceleration. not weight times acceleration:
> it WILL accelerate towards your crotch faster (not 6x faster) , but
> only because it is gaining less potential energy, leaving more of the
> energy you supply to accelerate the uni. and increase its kinetic
> energy ( the bit
> that hurts). *

Numbskull, that's what I said! I didn't misquote Newton's second law.
And Gerble knows what he's talking about, too. We know our science;
you're picking apart our nomenclature. Go fly a kite, you nitwit.

--
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12. ### hobgoblin Guest

Thats a bit harsh on Naomi, from a non-biased perspective, Naomi's posts
make the most sense of any of you guys'.

if your not going to get stupidly complex (anyone know the exact density
map of the earth / moon?) then a sphere like the earth can be reduced to
a point source at the centre from which gravity acts, and the inverse
square law works from there. So youd have to move 6372km away to quarter
your weight (not 10'), and I dont know ANYBODY who can hop that high.

Also, its a misconception that anything with air in it will explode in a
vacuum. By definition there is only 1 atmosphere (15psi) of pressure at
sea level on earth and you put about 40psi in a tire (less for trials)
which is 2.7 atmospheres. So the difference in pressure is about 1.7
atmospheres (25 psi) and most tire/inertube combos can take like
90psi.
And since your gonna weigh less you wouldnt need so much pressure
anyway.

Drag is proportional to speed. And unicycles are not known for their
speed, especially trials unis, so I dont expect that youd notice much
difference between jumping in a vacuum and in air. So if youve put the
effort into getting up there you may as well build an indoor trials
arena (with a high roof and lots of oxygen supplies, and a bar, and an
observation deck, space port, revolving restaurant, hotel, reasonably

--
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13. ### U-Turn Guest

If there is one thing Naomi is not, it's a nitwit.

--
U-Turn - As long as my feet keep movin'...

Weep in the dojo... laugh on the battlefield.
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johnfoss wrote:
> *
>
> Let's start with the Uni.com T-shirt scenario. An apollo Moon space
> suit. Very heavy pack, and very restricted movement. I would venture
> to say that you probably couldn't physically operate the unicycle in
> one of those suits. So let's assume it allows a little more freedom of
> movement, but still has a 70 pound (or so) pack on the back.
> *

I just couldn't resist this chance. This is a picture of me riding while
in an EOD8 bomb suit. It is around 75+ pounds, minus the matching helmet
which I am not wearing. I could manage around 30 or 40 feet at a time,
so I am assuming that in a space suit which would probobly have around
the same mobility and weight it would be possible to ride...

+----------------------------------------------------------------+
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is worth war is much worse. The person who has nothing for which he is
willing to fight, nothing which is more important than his own personal
safety, is a miserable creature and has no chance of being free unless
made so and kept so by the exertions of better men then himself."
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16. ### maestro8 Guest

> *I just couldn't resist this chance. This is a picture of me riding
> while in an EOD8 bomb suit.*

We need a picture of you in the suit on the 'Surly 4\" Monster'
(http://www.gb4mfg.com/temp/surly_monster/) with the helmet... riding
down some stairs. Yeah.

I'd buy the t-shirt _and_ the poster. Heck, I'd buy a few.

--
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17. ### Klaas Bil Guest

Since kindly correcting seems to be the thing to do on this thread,
here goes:

On Thu, 14 Apr 2005 07:31:18 -0500, "hobgoblin" wrote:

>Drag is proportional to speed.

Drag is dependent on speed, but not proportionally. It's some higher
power, the exponent of which is not constant and depends a.o. on
Reynolds Number.

>And unicycles are not known for their speed,

Huh? When a unicycle is ridden, it has some speed per definition.
People have discussed their speed on a unicycle at length. One might
argue that unicycles are not known for 'high' speed, but that just
depends on what you call 'high'. The speed on a Coker can be such that
drag is a significant factor.

--
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18. ### burnitalltwice Guest

i have a feeling this thread is gunna b up 4 a while since 4 sum reason
inteligence and unicyclist seem to be common

--
burnitalltwice - Something wholesum! v

VOTE FOR PEDRO!
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"Can a person with no ears wear glasses?"
"Isn't Disney World just a people trap operated by a mouse?"
"How about something nice and wholesome, like a triangle. Or a
toothpic."-BraveSirStupid
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19. ### maestro8 Guest

Klaas Bil wrote:
> *Secondly, I dispute your implied definition of 'proportional'. To me,
> in physics and mathematics 'proportional' is just shorthand for
> 'directly proportional' (also known as 'linearly proportional').
> *

I will second this observation. If you're gonna write out an equation
in shorthand (w/ variables) or longhand (in words) you better get your
powers right. Ferchrissakes, if Coulomb's law wasn't proportional to
1/r^2, we all wouldn't be here right now. Don't muck these things up!

> -Originally posted by burnitalltwice-
> *i have a feeling this thread is gunna b up 4 a while since 4 sum
> reason inteligence and unicyclist seem to be a common combo
> *

Point and counterpoint all in one beautifully crafted run-on...

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