David Nightingale - Felix Baumgartner's Jump

Anyone who's jumped off a haystack or played on a trampoline, knows the pleasurable feeling of weightlessness, wherein there are, for a fleeting moment, no more sagging body parts.

Felix Baumgartner, a 43-year old Austrian military parachutist, intentionally jumped from a capsule 24 miles up, on Oct 14, thus certainly knowing weightlessness for a decent amount of time. And what a fascinating lot of physics the man who fell from space experienced!

As climbers on Mt Everest (which is about 6 miles high) know, it gets colder and colder as one ascends, and the atmospheric pressure gets less. If one were to stick one's finger out of the window of an ordinary passenger jet, for example, flying at typically not much more than the height of Mt Everest, it would be roughly minus 70F, and not only would the finger expand, and freeze, but of course there'd be quite a sucking noise of cabin air rushing out...

Space craft orbits are at least 60 miles high. Baumgartner got to about 1/3 of this, or, from the jet passenger's point of view -- about 4 times higher than the jet.

Interestingly, it doesn't get colder and colder for ever; after about 7 miles or so the atmosphere stays at a more steady temperature and even warms up a little.

His helium-filled birthday-party balloon, the largest in the world, started relatively small, although obviously plenty large enough to lift his capsule. Here he sat in relative comfort, pressurized as in any jet liner, for two and a half hours, rising slowly through the ever thinner atmosphere. As high school physics students know the balloon floated upward, just because of Archimedes' Principle, with helium being lighter than air. And in just the same way that bubbles expand as they rise in a beer glass, so his balloon expanded, and expanded, and expanded until there was indeed the possibility of its bursting -- a situation that had to be carefully monitored of course. In the end, at about 24 miles high, the air was so rarefied that the average density of [balloon + capsule] was essentially the same as the density of the helium at that particular temperature and pressure, because (again as SAT high schoolers know) the density of a gas changes, unlike the density of a solid or a liquid. [Oh, I know there will be purists who want to say that solids and liquids change SLIGHTLY.]

So his balloon reached a height beyond which it couldn't go – and, if one had wanted to go higher, then an even larger balloon would have been needed.

Over 50 years ago Joe Kittinger jumped from 18 miles [~103,000 feet] – nearly Baumgartner's 24 miles [~ 128,000 feet] – and the now elderly Kittinger was very much involved as a helper with Baumgartner's record-breaking 9 minute fall. Yes, that's all it took; 9 minutes to come down again. Not all free-fall, because the last few miles were by parachute.

Back in 1971, a 17 yr old German High School girl, Juliane Koepcke, fell still strapped to her seat when her passenger jet was struck by lightning, which had ignited a fuel tank. Incredibly, she landed in the Peruvian rain forest with only a broken collarbone and a severely swollen eye, and managed to find her way by a stream to people who rescued her. Which brings up another point that science students know about: terminal velocity. A raindrop only accelerates up to the point where frictional drag becomes equal and opposite to weight.

Juliane would have reached a terminal velocity after just a few minutes, and with the seat still attached she would be going pretty fast but not too fast. In Baumgartner's case the air was so much more rarefied up there that he would fall a much greater distance before terminal velocity was reached – and thus (for actually about 4 minutes) he fell faster and faster – ultimately even faster than the speed of sound. The speed of sound is a little different up there (it varies with the square root of the temperature, so it's less than on the warmer ground) but all the measurements show that he exceeded the speed of sound at those heights. Also, in his own words, he felt nothing going through the sound barrier.

But what an incredibly interesting physics experiment: barometric pressure, temperatures of gases, Archimedes, gravity, volume expansion and the gas laws, dependence of speed of sound on pressure and density, you name it.

Nevertheless, if one wants to achieve weightlessness, albeit for just a nanosecond, then it's a bit safer just to fall down into a chair.

PS  Both the capsule and the balloon were later safely retrieved.