mercredi 6 juin 2018

Storm in a Teacup

Your reviewer took Physics A-level in 1992 and hasn't really touched it since. Helen Czerski has written the kind of book that she wishes had been a textbook, but couldn't really be, but which helps traverse the yawning chasm between what one studies and what happens in real life around this subject. Similar books exist for other natural sciences, and maths and economics. The BBC sometimes pulls some of it into radio shows, in which this author (a physicist at University College London who studies mostly bubbles) has contributed. It would be great if this stuff was on TV too (maybe it is)

Gravity is a perpetual free force (available since before free wifi and in more places) that perhaps sometimes seems limiting because it always pulls stuff down. But it can be used against itself--London's Tower Bridge has giant hidden counterweights on pivots so that when the thing does open (rare these days) very little lifting is actually going on. On much smaller scales the force that is surface tension (the molecules on the outside of a bit of liquid being less happy than the ones inside because they are not completely surrounded by their mates), can be exploited by using a towel to miraculously mop up spilt milk against the pull of gravity that spilt it. California's giant redwood trees make use of surface tension to raise continuous columns of water up to one hundred metres into the air to their uppermost leaves. And this perpetual anti-gravity stream can never be allowed to stop, because it can’t be re-started and the tree would die; but since they haven't died, the upward water flow has evidently always continued.

Gravity can also be overcome by spinning things, which can create more powerful forces acting in a different direction. This is why the curved ends of a bike race track have to be steeply banked. And it means that a centrifuge can separate a mixture in seconds that gravity would take many years to do. Things in a mixture separate if they have different density, because that gives them different hierarchies in the gravity league tables, as long as they don't have bigger forces pulling them together. In fact gravity is an exceptionally weak force really--when you get out of bed you are resisting the pull created by an entire planet. Satellites in orbit haven't escaped gravity, they are perpetually falling back to earth; it's just that they keep missing it.

All forms of energy harvesting (translation: every reason everywhere and always why we might be able to have cool stuff) involve getting in the way of an inexorable march to equilibrium (also known as maximum entropy but Ms Czerski avoids much talk of that). In fact the ability to delay or obstruct equilibrium is a decent marker of what life can be considered to be, so that if diverted equilibrium can be spotted elsewhere in the cosmos, that's probably as good as indication of other worldly life as it is possible to get (not that this fingerprint has been spotted yet).

Waves are fun. They don't move matter but can carry energy. Sometimes stuff too--when your reviewer was at a U2 gig in 2017 she participated in a kind of "Mexican wave" that was used to pass a giant flag around the perimeter of Twickenham stadium without anyone leaving their position. Ocean waves don't move the water much, hence sea birds can bob up and down on them. Surfers on the other hand can tap into the modulated dynamics and actually travel with the wave. That's because the wave has energy which surfers can capture for their sport. In a way it is what electromagnetic radiation (technical term for a type of really useful energy) does, and most fortunately it can carry zillions of information signals (mobile phone conversations, TV, everything on the internet, heat, light, what have you) all without any of it crashing into other bits (like actual surfers would if there were too many of them off the same beach). And the beach refracts ocean waves so that they hit it straight on, not unlike how other media (technical term for a big load of atoms of something or other) can refract other waves. Which means change their speed and therefore usually their direction. Actually this is why you've never really seen a light wave that was travelling at light speed, sorry, but it's a good thing really; very good in the sense of what else it makes possible. Like lenses and cameras.

It's not just humans who use waves either. At the bottom of the sea, sound is king because light hasn't ever made it there. Whales and dolphins are colour-blind because they need colour information way less than they need a hole in the head. They hear a tremendous amount of stuff though. The RMS titanic might not have sunk if radio tech had been a decade or two more evolved at the time (though twenty years earlier nobody would have known it had sunk until it was probably several weeks late to New York)

Waves can do a lot of damage too. Buildings today are constructed with great attention to their resonant frequency. Taipei's 101 tower has a gigantic pendulum between levels 87 and 92 to oppose and damp earthquake inspired oscillations. London's Millennium Bridge designers initially overlooked a more benign frequency which was people's footsteps, and it had to be closed for months shortly after the first journeys across it made people feel ill. Your reviewer's office building in the City of London audibly creaks in high winds--it's more stable because it does this.

Most of the earth's surface is water, which is a very unusual substance because of being less dense as a solid than as liquid. This didn't really help the Titanic whose crew and passengers would all have been better off if it was the other way around. But it makes it easier to chill a glass of Pimms, and it also allowed the polar explorer ship "Fram" to navigate over the Arctic Ocean using a special design that not only stopped it from being crushed by polar ice, but also made it get carried along by it (rather slowly; three years from Siberia to Greenland)

Birds bob their heads forwards as they walk in order to keep them in one fixed position for longer while the rest of the bird makes the same move (Ms Czersky tested this by putting a pigeon on a treadmill and observing that the head-bob vanished completely). Keeping one's head still is also why pirouetting skaters snap theirs around by 360 degrees and then wait for their bodies to catch up. For birds it is because their vision doesn't work quick enough to give them a good enough picture of where they are unless they arrange for this stop-motion pattern. For skaters though it is to limit the swirling of fluids in the inner ear, which is the human body's gyroscope and which would otherwise cause nausea. (Apparently proper pirouetting doesn't do that.)

There are many gems like this among the pages. Collected together in the way they are, properties of gravity, electromagnetism, surface tension and so on all start to look so staggeringly useful that the late Douglas Adams would probably take them as final conclusive proof of the non existence of god (who would refuse to provide such clear evidence that she is real). But this revelation is not that different from the one a sentient puddle has upon discovering that it sits in a natural indentation the exact same shape as itself--in other words--we and our fellow life forms are the only ones left who could possibly survive and thrive in such weirdness, so it naturally looks tailor made for us. This is brilliant.

via International Skeptics Forum

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