Quick link to Cocktail Party Physics: demon spawn
Maxwell’s demon, with a bit of a modern twist that makes it apply to laser cooling.
Category Archives: Physics
Come Sail Away
NASA to Attempt Historic Solar Sail Deployment
A few years ago, the Planetary Society attempted a mission like NanoSail-D called Cosmos I, but the launch vehicle failed and destroyed the undeployed spacecraft. Montgomery and team believe that NanoSail-D, however, will unfurl four gossamer wings from its pod in the blackness of space like a butterfly from a cocoon: movie.
“The structure is made of aluminum and space-age plastic,” says Montgomery. “The whole spacecraft weighs less than ten pounds. We carry it around in a special suitcase — airplane carry-on luggage size.” Fully opened, the kite-shaped sail spreads out to about 100 square feet of light-catching surface.
“A success would be huge for the future of space exploration,” Montgomery believes.
Not to burst any bubbles — a successful solar sail would be way cool — but “space age” technically just means it was invented after the Sputnik launch in 1957.
The Lumpy Gravity of the Moon
“The Moon is extraordinarily lumpy, gravitationally speaking,” Konopliv continues. “I don’t mean mountains or physical topography. I mean in mass. What appear to be flat seas of lunar lava have huge positive gravitational anomalies—that is, their mass and thus their gravitational fields are significantly stronger than the rest of the lunar crust.” Known as mass concentrations or “mascons,” there are five big ones on the front side of the Moon facing Earth, all in lunar maria (Latin for “seas”) and visible in binoculars from Earth.
Blue/violet is reduced acceleration, yellow/red is increased acceleration.
h/t to D H
Lab Tricks
No, not that kind of trick, you pervert*.
I was doing some homemade wiring, and whether it’s power or signal, you generally want to use twisted-pair (or triplet, or quad, etc.). It’s faster than running all of the single-wire, so there’s a labor-saving aspect to it, but there’s a data quality aspect to it as well.
Any time you have a pair of wires that completes a circuit, you have to worry about ground loops and other signal pickup. If the wires are separated, and the magnetic field that runs through them changes, Faraday’s law tells you that you’ll add some current or a potential difference to the loop. The bigger the loop, the more flux you’ll be capturing. If you write this onto the common ground for your experiment, you will be putting this signal onto all of your equipment. And this is not just the earth’s field — everything radiates. A loop is an antenna for picking up 50 or 60 Hz power and also any other frequency equipment you use in the lab. (Early on in my current job, in the dark days before I had a CD-burner, much less an iPod, I tried listening to the radio in the lab. At one point we added an Acousto-optic modulator and started driving it a smidge above 100 MHz, which was almost the same frequency as the local oldies station, and I couldn’t get that station anymore because of the interference). This will get written on to your signal lines, and will get picked up by power lines, which then writes it on to all of that precision equipment you soldered together, and forgot to add bypass capacitors everyplace you needed them) . Chasing down ground loops is a big pain, as is filtering out noise. Twisting the wires means that the net current flow of any power signal is zero, as current input is as close as it can be to the return path, so the far-field radiation — basically anything further away than the diameter of the wire bundle — is nonexistent. If it’s a data line, it doesn’t look like an antenna, except perhaps for extremely high frequencies — the area for magnetic flux is vanishingly small, so it has no opportunity to pick up a signal.
So you want twisted-pair, but the commercial pickings can be slim for the exact wire type you might want to use, and besides, you want to color-code what you’re doing. So here’s the trick: use a drill. Clamp on to the wires with the chuck, pull taught and squeeze the trigger. Wind up to a reasonable pitch and — I cannot emphasize this enough — release the chuck before lessening the linear tension on the wires. You’ve added a lot of “twist” to the wires, and they will untwist. If you release the linear tension first —trust me on this — it will jumble up like a telephone cord. (If you’re under 30 and don’t understand the phrase “telephone cord,” it’s the phone you’ve seen at your grandparents’ house, perhaps in the basement. The phone might even have a round disc on the front, with ten holes in it around the perimeter)
*my conclusion after perusing the somewhat disquieting search-engine stats. Suffice to say that using “animal robo-p*rn” in a title isn’t leading to searches that are attracting science-minded folk to the post.
Photochrome
Photochrome
You give us those nice bright colors
You give us the greens of chemistry
Makes you think all the world’s a funky lab, oh yeah!
Zap the molecule with UV and it turns green. This is due (as I understand it) to the molecule changing to another state (isomer) — and not simply fluorescence — where it then has a different absorption spectrum, so in this example it looks green. When you remove the UV, it reverts to the original state and becomes clear again, and it’s doing this quite rapidly.
Gooooooaaaaaaaaaal!
via kottke
In celebration of Euro 2008, public prankster and more-than-fair soccer striker Rémi Gaillard made the following video of himself using the urban landscape as a soccer pitch. Gaillard scores goals into police vans, trash cans, open windows, etc. to the annoyance of his oblivious goalies.
I love the one where his first shot triggers the motion sensor and he “scores” on a rebound . . . at the police station.
It's a Quarter Past 'Dragon Eats the Sun'
Narrowing down some historical dates with astronomy
Marcelo Magnasco and Constantino Baikouzis identified four astronomical events in the epic poem [The Odyssey] and calculated dates within 100 years of the fall of Troy that would fit in with the events described around Odysseus’s return home and the ensuing slaughter of men propositioning his wife. April 16, 1178 BCE was what they came up with
I hope that the language tutors prepositioning his wife were spared, but Homer was silent about that. Anyway, there’s also a correction to the dates for Caesar’s invasion of England, based on the tides.
And last week, Matt explained more over at Built on Facts
On June 15, 763 BC a total eclipse appeared in Assyria. Mentioned both in Assyrian records and (possibly) the Biblical book of Amos, it’s the oldest specific date of which I’m aware in ancient near eastern history. More spectacularly but later, an eclipse on May 28, 585 BC ended a battle between the Medes and the Lydians by terrifying the combatants into an immediate peace agreement. If you don’t count an eclipse by itself as being a historical event, I believe this is the single oldest event which can be pinned to a specific date.
Ghostly Visages
No, not of an alien at the window.
Here’s a little movie showing atoms being trapped and mistreated. What you’re seeing is a video of the monitor that’s hooked up to a little IR camera on the vacuum chamber. The really bright spot that’s squirming around a little are the atoms, or technically, the fluorescence from the atoms. There are probably more than a Sagan of them (i.e. biilliyuns) at about a milliKelvin or so in temperature (which is considered warm!) because it hasn’t been fine-tuned yet. The bluish circle is reflected light off of a flange, and there’s some other scattered light visible.
About 10 seconds in, the trap’s magnetic field is turned off, and the atoms squirt off to the side. A second or two later the field is turned on again, and the trap fills up. If the lasers were properly aligned and balanced, and the earth’s magnetic field were either shielded or zeroed out with trim coils, then what you would see is a nice uniform expansion into a much colder (microKelvin-ish) optical molasses, but the earth’s field is still present here, so that gives rise to an imbalanced residual force which is small compared to the trapping force, so you only really notice it when the trapping field is turned off. The molasses impedes the motion of the atoms, but doesn’t technically trap them, i.e. it doesn’t define a point where the atoms should be, so when only the lasers are there, the atoms would normally just drift through, very slowly. But here they’re being shoved a little bit.
The accelerations involved here are large — these atoms can scatter a million photons a second, give or take, depending on the exact laser frequency, so even though an individual scatter changes the atom’s speed by about 6 mm/sec, when you scatter them that rapidly you can get accelerations of hundreds of g’s. But in the situation here, where the atoms are almost at rest, that’s balanced by an equally large acceleration from an opposing laser.
I Can Geek Anything Up
Lady spinning on escalator handrails. Nominally the net force is zero, assuming each rail exerts the same magnitude of force, but there may be some differences depending on what part of her body is in contact, or the escalator speeds. They each exert a torque in the same direction, though, so she spins.
via Kottke
Give My Creature LIFE
Or at least make it spin a little. A simple motor: battery, magnet and wire.
Magnetic field sees a changing current and that results in a force, which gives you a motor. Quite similar to the Faraday motor, but then, he was allowed to play with mercury (and he never wore a bike helmet, either)
Update: Give MY creature life. Built one myself this afternoon, and even figured out how to upload it to YouTube. She may not look as pretty as these other motors, but she loves to spin. (First attempt didn’t go so well, but I found lighter wire that was still stiff)