# Moon trials

Wow i just got hit in the face by this awesome idea. someone has prolly already thought of it but imagine riding on the moon that would be sick. woe i saw the astronaight tshirt at unicycle.com and i was like dude that’d be sweet wo except 4 the restricting suit prolly would fuck up he riding mojo. but yeh woo that’d be kool

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.

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!!

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.

well if you go over a bump you will be sent sailing, it would just be weird

that doesnt mean physics dont work out

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.

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

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.

sigh, all the best arguments are ruined by someone who comes along and actually knows what s/he’s talking about. just kiddin Josie!

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.

i thought it was 2% of earths gravity

aside from massive hops, i seeing BACK FLIPS and 1080’s and stuff… that would be sweet

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.

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.

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…

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

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.

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!