the world's craziest idea - Page 2

tholub · 2008-08-02, 10:47 PM

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.

hobo_chuck · 2008-08-02, 10:51 PM

Don't underestimate the power of 15 pounds added onto normal stress on a frame...but it still isn't a major problem.

skrobo · 2008-08-02, 11:42 PM

its 15lbs in every direction at all times... not just 15lbs resting on top of it.

tholub · 2008-08-02, 11:49 PM

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.

petad · 2008-08-03, 12:38 AM

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.

hobo_chuck · 2008-08-03, 12:42 AM

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?

hobo_chuck · 2008-08-03, 12:42 AM

Quote:

Originally Posted by petad

or scraping the paint off your uni

I just did that. It's 10g lighter now.

mscalisi · 2008-08-03, 12:44 AM

Why not just tie some balloons to your helmet. You can use way more helium that way therefore having much more benefit.

Nicf · 2008-08-03, 12:46 AM

wow you must have put allot of thoght into that one!

sigve · 2008-08-03, 01:29 AM

why put it in your uni, it's like 10 times cooler to talk with it

Unreal-Wheel · 2008-08-03, 01:30 AM

Quote:

Originally Posted by mscalisi

Why not just tie some balloons to your helmet

Helmet

Wheel Rider · 2008-08-03, 01:53 AM

We kicked this idea around last year.

http://www.unicyclist.com/forums/sho...ghlight=helium

ivan · 2008-08-03, 08:44 AM

Why not store anti-matter inside the seatpost?

hobo_chuck · 2008-08-03, 04:14 PM

Quote:

Originally Posted by ivan

Why not store anti-matter inside the seatpost?

boom.

kurtismyhead · 2008-08-03, 04:23 PM

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.

2008-08-02, 11:42 PM	#18
skrobo jumps stuff Join Date: May 2006 Location: Corpus Christi TX Age: 24 Posts: 4,426	its 15lbs in every direction at all times... not just 15lbs resting on top of it. __________________ ><> Unicycle For Christ <>< MY VIDEOS World Record 94cm Highest Hop (rolling) 308cm Longest Hop (10 feet) 210cm Static Flat Gap

2008-08-03, 12:38 AM	#20
petad ... Join Date: Apr 2008 Location: CHASKA, MN, USA Age: 18 Posts: 674	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. __________________ )--360unispin-O 2nd )-Crankflip-'O, 5th Last edited by petad; 2008-08-03 at 12:40 AM.

2008-08-03, 12:44 AM	#23
mscalisi Registered User Join Date: Dec 2003 Location: Alameda, CA Age: 40 Posts: 1,955	Why not just tie some balloons to your helmet. You can use way more helium that way therefore having much more benefit. __________________ ><> Unicycle for (reducing the) Buddha <><

2008-08-03, 01:29 AM	#25
sigve Trials rider=) Join Date: Oct 2007 Location: Norway, Drammen, Øren! Age: 21 Posts: 380	why put it in your uni, it's like 10 times cooler to talk with it __________________ Sorry for my english it's not great, but I work hard to get it better

2008-08-03, 01:53 AM	#27
Wheel Rider From the Over 50 Group Join Date: Aug 2005 Location: Memphis, TN, USA Age: 60 Posts: 1,205	We kicked this idea around last year. http://www.unicyclist.com/forums/sho...ghlight=helium __________________ A man can fail many times but he isn't a failure until he begins to blame someone else. - Waite Phillips The art of medicine consists of keeping the patient amused while nature heals the disease. - Voltaire

2008-08-02, 10:51 PM	#17
hobo_chuck Why me? Join Date: Jan 2007 Location: Rocky Mountain HIIIIIIIIIIIGH!! Co-lo-ra-do...... Posts: 1,645	Don't underestimate the power of 15 pounds added onto normal stress on a frame...but it still isn't a major problem.

2008-08-03, 12:46 AM	#24
Nicf going to learn standwalk^^ Join Date: Feb 2008 Location: Manitoba St. Malo Age: 19 Posts: 562	wow you must have put allot of thoght into that one!

2008-08-03, 08:44 AM	#28
ivan Non-Danish Girl Join Date: Jul 2006 Location: Prague, Czech Republic Age: 25 Posts: 7,210	Why not store anti-matter inside the seatpost? __________________ Did you know that lighter flame smells like burnt nose hair? Entropy isn't what it used to be. Last edited by ivan; 2008-08-03 at 08:45 AM.

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