Re: Moon trials

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

  1. Evan Byrne

    Evan Byrne Guest

    well the phisics of it dont quite work out, if you tryed to hop you
    would be sent 20 to 40 feet into the air. Also wearing a suit would be
    hard to do while riding.


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  2. James_Potter

    James_Potter Guest

    ehh, that would be pretty cool I guess. except we should just do it in a
    spacestation instead, that way you could have the amount of gravity you
    wanted, whatever that amount might be, AND you wouldn't need to wear
    anything!!


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  3. Evan Byrne wrote:
    > *well the phisics of it dont quite work out, if you tryed to hop you
    > would be sent 20 to 40 feet into the air. Also wearing a suit would be
    > hard to do while riding. *



    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.


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  4. Evan Byrne

    Evan Byrne Guest

  5. drewation

    drewation Guest

    Evan Byrne wrote:
    > *well if you go over a bump you will be sent sailing, it would just be
    > weird *



    that doesnt mean physics dont work out :rolleyes:


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  6. halfbike

    halfbike Guest

    Gravity on the moon is one sixth of the earths. So If I hop two feet on
    earth I would just 12 feet on the moon. But wouldn't I need a special
    tire so my tire wouldn't pop because of the vacume of space???Plus a
    space suit is heavy
    which would cause you to jump less.


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  7. halfbike wrote:
    > *Gravity on the moon is one sixth of the earths. So If I hop two feet
    > on earth I would just 12 feet on the moon. But wouldn't I need a
    > special tire so my tire wouldn't pop because of the vacume of
    > space???Plus a space suit is heavy
    > which would cause you to jump less. *



    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.


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  8. James_Potter

    James_Potter Guest

    TheObieOne3226 wrote:
    > *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. *



    well most people can get at least 20 inches seat in, which makes 10 feet
    on the moon.


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  9. Josie

    Josie Guest

    Before your legs attrophy to the lesser gravity, you will be able to get
    approximately the same amount of kinetic energy in a hop.

    KE = mass * gravity * height. So the height is linear to the
    acceleration due to gravity and you will go 6 times as high. The cool
    thing is that the time spent in the air to reach the apex is h = 1/2 *
    g*t^2 so t = sqrt (2h/g), so comparing the relative values, you will
    also be in the air 6 times as long and able to jump 6 times as far.

    So if you have a 6 foot side hop, you would have a 36 foot side hop on
    the moon. And that would be insane.


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  10. James_Potter

    James_Potter Guest

  11. Josie wrote:
    > *KE = mass * gravity * height. So the height is linear to the
    > acceleration due to gravity and you will go 6 times as high. *




    No, you're wrong.


    Let's say I have a 30'' sidehop. My leg power provides maybe 15'' of
    that. The other 15'' is from tucking the unicycle. This is unaffected by
    the lesser gravity. So, in this example...


    15x6 = 90 + 15 =105


    105 does not equal 6 times 30.


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  12. Evan Byrne

    Evan Byrne Guest

  13. THE dave

    THE dave Guest

  14. Josie

    Josie Guest

    TheObieOne3226 wrote:
    > ...My leg power provides maybe 15'' of that



    Obie is funny. You are correct in that I was not correct.

    There are two things which add up to horizontal displacement. The firsh
    is horizontal velocity * air time, which gives the displacement of your
    center of mass. The second is the horizontal distance between where the
    wheel touches the ground and your center of mass from before leaving the
    ground and at the point which you touch the ground again.

    So the question is how much you are leaning over when you leave the
    ground and when you land. Multiply the distance in the middle by 6.

    Of course, with 1/6 the gravity you have 1/6 the friction so it will
    probably be pretty slippery unless you have 600lbs on you which would
    take care of being able to jump any higher than you can on earth.


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  15. 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. You double the distance and the force of
    gravity decreases by a factor of 4, because 2 squared=4. This same law
    dictates the observed intensity of light, the pull of magnetic fields,
    and the intensity of electrical fields. If we lived in 4 dimensions it'd
    be the inverse cube law, and 2D it'd be the inverse law. Examining
    observed surface areas explains why. All of this leads to the
    explanation that even though the moon is more than 1/6 the mass of
    earth, it isn't very dense, so the diameter means the strength of
    gravity is disproportionately low compared to the mass.

    *yes, wrong units, it should be newtons, but i'm trying to use familiar
    units here.

    As for a special tire, no, you wouldn't need one.** Air pressure in a
    tire is relative, so if the ambient pressure outside is 0 psi, then the
    tire will have a pressure of 20 psi with 20 psi of air in it. If the
    outside air pressure is 10 psi, and the inside air pressure is 30 psi,
    the effective pressure is 20 psi.

    *Ignoring the need for a rubber that would resist temps of <-300 degrees
    F and >250 degrees F. Also, anything bvlack would absorb a lot of
    sunlight, heating it up greatly.


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  16. James_Potter

    James_Potter Guest

    Josie wrote:
    > *So the question is how much you are leaning over when you leave the
    > ground and when you land. Multiply the distance in the middle by 6.*



    are you talking about horizontal sidehops, or vertical sidehops? I think
    Obie is talking about vertical, and it sounds like you're talking about
    vertical.... I could be wrong though....


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  17. spyder

    spyder Guest

    THE dave wrote:
    > *... and 1080's and stuff... *



    I'd probably barf in my suit. That's alot of turning.


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  18. PhilS

    PhilS Guest

    well you might as well take in some more variables.... are we talking
    indoors or out?
    indoors, you would have to remember that air friction stays the same,
    meaning your height/distance would be less than proportional.
    in the vacume there is no air friction, (there's no air)so it would
    increase your height/distance.


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  19. maestro8

    maestro8 Guest

    PhilS wrote:
    > *in the vacume there is no air friction, (there's no air)so it would
    > increase your height/distance. *



    The drag force is proportional to the square of one's velocity. Unless
    you're talking rolling hops on a Coker at full sprint, I doubt you'd
    notice any more than a 1% difference in distance in a vacuum versus air
    at standard temperature and pressure.

    The figure that Josie stated earlier (mass * gravity * height) is
    potential energy, not kinetic. Josie is correct, however, in stating
    that one's hop height (not including the unicycle being pulled up) would
    be about six times as much as on Earth.

    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 :)

    Considering a side hop things get much more interesting. Having legs
    with 6x normal power, one would not have to extend his legs as much
    before landing; he may be able to land fully compressed and get away
    with just a little tire-in-the-butt, hence extending his side hop
    "range".

    Friction is critical for both take-off and landing, however, so one's
    technique would need to be impeccable to reproduce a massive side hop on
    the moon without faceplanting on takeoff. Even if one could stick the
    takeoff, the landing would involve a good bit of sliding...

    The "slippery" factor isn't so much a consequence of reduced gravity as
    it is a consequence of the moon's dusty ground cover. Before
    calculating your 6x improvement, measure your hop height and width in
    light sand or clay. Has anyone tried this and compared it to their
    "street" measurements?

    Now, if there were a skate park on the moon, we wouldn't have to worry
    about the soil. Anyone done any research into concrete drying time in
    outer space? Could we stir a little quikcrete into lunar soil and make
    concrete this way? I'm sure NASA has it all figured out...

    Kudos to all, great imaginations, great thread!


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  20. johnfoss

    johnfoss Guest

    I have thought many times about riding on the moon, in zero gee, or in
    space stations with various rotating ways to make quasi-gravity (with
    precession).

    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.

    1. You would have crap traction. You don't weigh what you used to, and
    the ground is dusty. You would have to learn how to accelerate and slow
    down without skidding/spinning.

    2. You would have to learn to compensate for the heavy pack. Though it
    would weigh only 70/6 pounds, it would still be a significant percentage
    of your total weight.

    3. You should be able to hop like crazy, even with a "regular" tire. A
    fatter tire would give you more hop.

    4. Nobody mentioned anything about weight vs. mass. Though you would
    *weigh* less, your mass would remain the same. This could translate into
    problems when you land those big drops or hops. You would accelerate
    downward more slowly, but still increasing at the same rate. In other
    words, you might land pretty hard.

    Side note: This reminds me of one of those unusual experiments the
    astronauts conducted on the Moon. The guy had a (rock) hammer in one
    hand, and a feather in the other. He was talking about acceleration
    (that 20' per second-per second thing), and how would it be affected in
    a vacuum? Which would fall faster? The hammer, of course, because it
    weighs more, right?

    He lets go of both, and they both drop like rocks. One of the weirdest
    things I've ever seen. No air, so the feather accelerates downard at the
    same rate as the hammer.

    So on the moon, you would only fall as fast as a feather, but that's the
    same speed as a hammer (or a Lunar Rover).

    But riding on the lunar surface, to me, would be far less interesting
    than riding in a gym on the moon. Never mind the air. I want to dress
    comfortably and start inventing new Freestyle tricks! All the standard
    stuff should be learnable in a few days. Then it would be time to work
    on stuff that would be totally impossible on Earth.

    When that got boring, if the room was big enough, I'd make myself a pair
    of wings and learn to fly in there...


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