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There is an art/science video clip on youtube, by Simon Faithful, called Escape Vehicle no.6 (chair in space). It shows a simple steel office chair, tied to a weather balloon, ascending into the upper reaches of the atmosphere. Apparently it reaches about 30km above sea level. It's quite a beautiful clip.

At the start, the chair rises quite violently, as it is buffetted by surface turbulence, as would be expected. After a while (2:07-2:33, I suppose once it gets above the planetary boundary layer), the ascent becomes fairly smooth - there is still a lot of movement, but it's not so violent. Then at 2:45, when the chair is near the top of it's ascent (~30km), suddenly things start getting really violent again, and the chair looses a leg, then half the back is torn off, and then the chair is apparently torn from the rope, and disappears.

What forces would cause such a violent disintegration of what is a reasonably strong object, in such a thin atmosphere?

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A guess: at -60 below 0 the metal becomes brittle and breaks off, which changes the stability of the system and continuous the disintegration. –  anna v Nov 21 '12 at 13:04
    
@annav: good point. That totally slipped my mind. –  naught101 Nov 21 '12 at 13:06
    
That does look pretty turbulent for something so high up. –  Emilio Pisanty Nov 21 '12 at 20:42
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up vote 2 down vote accepted

The flight actually took 25 minutes, the video you linked to is edited down, and the later stages of it look pretty turbulent. I'd guess it was the shaking that eventually broke off the chair leg, possibly due to metal fatigue. Note that the leg broke off after the balloon had burst and while the chair was falling back to Earth.

As Anna says, the low temperature may well have been a factor. The ductile-brittle transition for mild steel is around -50C so at -60C it would be a lot more brittle than at room temperature. From the way the leg broke off I'd guess it was the weld that failed rather than the steel itself.

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I hadn't realised the balloon broke, but I guess that's the obvious cause of such turbulence. The same thing happens in the Toshiba version. I guess I missed it because I assumed the camera would start flipping, but I guess it was weighted, to it would stay fairly vertical... –  naught101 Nov 21 '12 at 23:50
    
@John: That video bothers me. If the chair's being jerked around like that, what is the camera attached to? What keeps the camera focused on the chair? –  Mike Dunlavey Nov 28 '12 at 14:11
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