View previous topic | View next topic

Helium

Page 1 of 8
Goto page 1, 2, 3, 4, 5, 6, 7, 8  Next

Ellie
601672.  Thu Aug 20, 2009 10:52 am Reply with quote

(EDIT: I just watched the Christmas episode of the B series and realised the Helium trap has already been baited, set, and sprung on the unfortunate Alan. D'oh.)


What's creepy about helium?

APART from the voice (which changes the timbre by the way, not the pitch).

Helium exists as a gas except in extreme conditions, but if you can persuade it to liquid form (at below 2.1768 kelvin, -271C, -455.48F), it turns into helium II, a quite interesting superfluid.

Apart from having no measurable viscosity*, hellium II creeps. If kept in a super-cooled but unsealed jar, it will creep out along the sides in search of warmer regions, where it will evaporate. It's 30 nm thick whatever the surface of the container. It will also equalise its own level if there are two possible containers in the same unit--



Basically, a sort of chemical, squeaky Great Escape. "Take me with you!"


*Well, when measured flowing through capillaries as thin as 10−7 to 10−8m it doesn't. It does when it's measured flowing between two moving discs. This is currently explained by the two-fluid theory, which essentially states that liquid helium II is half shiny superfluid atoms (too super to be viscous), and half boring old normal atoms.

Source, predictably: http://en.wikipedia.org/wiki/Helium#Scientific_discoveries
See also:
Creeping Helium II Study

 
Pyriform
606702.  Tue Sep 01, 2009 5:46 pm Reply with quote

That is really QI.

The only other interesting thing I know about helium is that it was discovered on the Sun before it was found on Earth - hence the name.

 
Davini994
641430.  Sat Nov 28, 2009 11:03 am Reply with quote

Helium filled rugby balls go further.

 
Sadurian Mike
641438.  Sat Nov 28, 2009 11:19 am Reply with quote

I just like the happy helium container in the OP.

 
Spud McLaren
641446.  Sat Nov 28, 2009 11:39 am Reply with quote

Sadurian Mike wrote:
I just like the happy helium container in the OP.

It contained nitrous oxide before.

 
Spud McLaren
641448.  Sat Nov 28, 2009 11:49 am Reply with quote

Davini994 wrote:
Helium filled rugby balls go further.


QI!

 
Efros
641494.  Sat Nov 28, 2009 1:23 pm Reply with quote

Davini994 wrote:
Helium filled rugby balls go further.



Mythbusted
http://en.wikipedia.org/wiki/MythBusters_%282006_season%29#Helium_Football

 
Davini994
641501.  Sat Nov 28, 2009 1:56 pm Reply with quote

Well, El-Masri can't normally kick a ball 100 meters, and it's a standard NRL ball other than the helium. So unless there's an explanation for that, the empirical evidence has to win out over the principals on the linky:

Quote:
Under the same amount of impulse force under the same atmospheric conditions, balls filled with helium showed no significant difference from balls filled with compressed air. It was also shown that, under the same impulse, both types of balls had the same initial velocity; since the helium-filled balls have a lower mass than the air-filled ones, the helium-filled balls have less inertia in flight: in fact, they may perform worse than air-filled balls over larger distances.

What the bolded bit contradicts Newtons 2nd law if one is lighter than the other.

The last bit suggests that they haven't actually tested it:

Quote:
in fact, they may perform worse than air-filled balls over larger distances.

There are other possible reasons not examined as to why it may fly further, e.g. it may accelerate down significantly slower due to the increased buoyancy.

 
Flash
641504.  Sat Nov 28, 2009 2:14 pm Reply with quote

Maybe it was a sort of placebo effect - it would have been interesting (and more rigorous) to see what would have happened if he had been given an ordinary ball, but told that it was full of helium.

 
PDR
641507.  Sat Nov 28, 2009 2:28 pm Reply with quote

It is often stated that part of the reason for the Hundenberg disaster was the american refusal to sell helium to nazi germany. This is untrue on many levels:

1. Hindenberg was designed from the outset to use hydrogen; use of helium (which has a greater density and thus produces less lift) would have reduced the maximum fuel capacity to a point where it would only have been able to achieve transatlantic range in favourable wind conditions.

2. Helium was sufficiently expensive that it is doubtful that its use in commercial airships would have been commercially viable. Even today the RAQF's barrage ballons (used for paratroop training) are hydrogen-filled because of the cost difference (tens of pence per cubic foot rather than the few quid a tonne for hydrogen).

3. Helium will diffuse through most materials quite quickly, and the gasbag technology of the thirties meant that it needed frequent topping up. This would again have threatened both the transatlantic endurance and the commercial viability for the Hindenberg.

4. (saving the best until last) We now know the hydrogen had nothing to do with the explosion or the crash. The explosion was caused by the failure to electrically bond laced-in fabric access panels in the skin. This caused arcing between panels after passing through areas of differing electrical potential (on the fateful day Hindenberg cruised around thunderstorms waiting for the weather to clear before docking). The arcing ignited the fabric skinning which, in an amazing piece of poor design, was coated with iron-oxide-based anti UV primer followed by aluminium dope (aluminium dust in a cellulose laquer medium). Iron oxide and aluminium mixtures when ignited produce the "thermite" reaction, in which the oxygen ion swaps tpo the aluminium to form aluminium oxide, iron and LOTS of heat. If you watch the film of the burning Hindenberg you can actually SEE the globules of moulten iron being ejected from the burning fabric. Once started a thermite reaction is esentially unextinguishable, so even without the hydrogen the skin would have burned away, rupturing the gasbags and causing the airship to stop "floating in the air in precisely the same way bricks don't".

PDR

 
Efros
641524.  Sat Nov 28, 2009 3:25 pm Reply with quote

Davini994 wrote:
Well, El-Masri can't normally kick a ball 100 meters, and it's a standard NRL ball other than the helium. So unless there's an explanation for that, the empirical evidence has to win out over the principals on the linky:

Quote:
Under the same amount of impulse force under the same atmospheric conditions, balls filled with helium showed no significant difference from balls filled with compressed air. It was also shown that, under the same impulse, both types of balls had the same initial velocity; since the helium-filled balls have a lower mass than the air-filled ones, the helium-filled balls have less inertia in flight: in fact, they may perform worse than air-filled balls over larger distances.

What the bolded bit contradicts Newtons 2nd law if one is lighter than the other.

The last bit suggests that they haven't actually tested it:

Quote:
in fact, they may perform worse than air-filled balls over larger distances.

There are other possible reasons not examined as to why it may fly further, e.g. it may accelerate down significantly slower due to the increased buoyancy.


The main problem with both mythbusters and that aussie show is that they used a human kicker. A scratchpad calculation of an american football's mass inflated with He compared to one inflated with air gives a difference of about 2g, this makes some assumptions, volume of football 1L, pressure 1.8 atmospheres, molar mass of air =29g. 2g is not a lot, certainly small enough to make a nonsense of any by the eye measurements and also small enough to not affect the the kick by too much.

1/22.4 = no of moles of gas in a football =0.04464 mol

0.04464 x 1.8 = no of moles at 1.8 atm = 0.0804 mol

4 x 0.0804 = mass of helium = 0.3214 g

29 x 0.0804 = mass of air = 2.3304g

diff in mass = 2.009g


Last edited by Efros on Sat Nov 28, 2009 3:34 pm; edited 1 time in total

 
Posital
641525.  Sat Nov 28, 2009 3:32 pm Reply with quote

Quote:
A source at CERN, the European lab hosting the accelerator, says that the quench caused one tonne of superfluid helium — about 1% of the LHC’s total — to escape.
So how many footballs could they have filled with that?

 
Efros
641528.  Sat Nov 28, 2009 3:38 pm Reply with quote

3111387.679 footballs, approximately

1 tonne = 1000 kg = 1000000 g

mass of He in a football = 0.3214g

1000000/.3214 = 3111387.679 footballs.

Wonder if that would fill the Albert Hall.

 
bemahan
641533.  Sat Nov 28, 2009 3:46 pm Reply with quote

I don't know but you can fit 13 Albert Halls into the O2. Allegedly.

 
Posital
641544.  Sat Nov 28, 2009 4:03 pm Reply with quote

The Albert Hall has a volume of 3060000 cubic feet.

I want to know how many balls it takes fill the Albert Hall!

We have to count them all!

 

Page 1 of 8
Goto page 1, 2, 3, 4, 5, 6, 7, 8  Next

All times are GMT - 5 Hours


Display posts from previous:   

Search Search Forums

Powered by phpBB © 2001, 2002 phpBB Group