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Old 2008-08-02, 10:47 PM   #16
tholub
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Wow, a lot of bad physics in this thread.

Quote:
Originally Posted by Emile.m
If there's no air, no gaz, no nothing inside the frame, it would crush because of the atmospheric pressure.
How high do you think atmospheric pressure is? Barometic pressure at sea level is 15 psi. Someone can calculate the yield strength of steel or aluminum, but I assure you that it's well above 15 psi. The strength of your frame is based on its own structural integrity, not on the air inside it holding it together. Air is highly compressible in any case.

Quote:
Originally Posted by catinabag1
even if the uni is lighter, it still has the same mass.
As noted, the unicycle would have less mass, for essentially the same reason that a balloon filled with air has less mass than a balloon filled with water.

Quote:
Originally Posted by Joseppi
Helium is lighter than air because it is less dense. Ergo, to fill a tire properly with helium, you would need more helium than you would need normal air in order to get enough pressure in the tire.
Ideal gas law: PV=NRT. Pressure in an ideal gas is a function of the number of atoms of gas, along with volume and temperature. The molecular weight of the atoms is not important; that's why helium balloons float. (NB: The composition of the gas can make a difference, because real gases do not behave ideally, but for most purposes the ideal gas law is a good approximation.)


All that being said, it is correct that the real effect of filling any part of your unicycle with helium is far too small to be worth doing.
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Old 2008-08-02, 10:51 PM   #17
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Don't underestimate the power of 15 pounds added onto normal stress on a frame...but it still isn't a major problem.
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Old 2008-08-02, 11:42 PM   #18
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its 15lbs in every direction at all times... not just 15lbs resting on top of it.
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Old 2008-08-02, 11:49 PM   #19
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Quote:
Originally Posted by skrobo
its 15lbs in every direction at all times... not just 15lbs resting on top of it.
That's still trivial in this context. Think about the force of a 200-pound person-plus-pack landing a 2' drop; I'm not going to bother calculating it, but it's probably two orders of magnitude higher than 30 psi. And still our tubes don't fail in the center; they fail at the weld, which is not where an internal vacuum would apply most of its force.
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Old 2008-08-03, 12:38 AM   #20
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Why not fill the tire with hydrogen? It weighs half as much as helium. But still, losing even a pound or two, or wearing lighter clothing, or scraping the paint off your uni, would probably have a bigger affect.

Last edited by petad; 2008-08-03 at 12:40 AM.
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Old 2008-08-03, 12:42 AM   #21
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Quote:
Originally Posted by tholub
That's still trivial in this context. Think about the force of a 200-pound person-plus-pack landing a 2' drop; I'm not going to bother calculating it, but it's probably two orders of magnitude higher than 30 psi. And still our tubes don't fail in the center; they fail at the weld, which is not where an internal vacuum would apply most of its force.
Way to re-word the first thing I said on that so it sounds smart
15psi could push a near-bend past the limit.
This is highly unlikely(say you run over your uni with a car and the frame is laying on a rail in just the wrong spot), but as air is so light in any case, why are we still discussing this?
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Old 2008-08-03, 12:42 AM   #22
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Quote:
Originally Posted by petad
or scraping the paint off your uni
I just did that. It's 10g lighter now.
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Old 2008-08-03, 12:44 AM   #23
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Why not just tie some balloons to your helmet. You can use way more helium that way therefore having much more benefit.
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Old 2008-08-03, 12:46 AM   #24
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wow you must have put allot of thoght into that one!
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Old 2008-08-03, 01:29 AM   #25
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why put it in your uni, it's like 10 times cooler to talk with it
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Old 2008-08-03, 01:30 AM   #26
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Quote:
Originally Posted by mscalisi
Why not just tie some balloons to your helmet
Helmet

Last edited by Unreal-Wheel; 2008-08-03 at 01:31 AM.
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Old 2008-08-03, 01:53 AM   #27
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We kicked this idea around last year.

http://www.unicyclist.com/forums/sho...ghlight=helium
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Old 2008-08-03, 08:44 AM   #28
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Why not store anti-matter inside the seatpost?
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Last edited by ivan; 2008-08-03 at 08:45 AM.
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Old 2008-08-03, 04:14 PM   #29
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Quote:
Originally Posted by ivan
Why not store anti-matter inside the seatpost?
boom.
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Old 2008-08-03, 04:23 PM   #30
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Quote:
Originally Posted by ivan
Why not store anti-matter inside the seatpost?
First of all, anti-matter combined with matter creates huge explosions, didn't you read Angels and Demons?

Secondly, I love this place. When i have a bad day I just read the latest inane post and i become happy.
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