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Count the colours

2 February 2010 — dan

Here's a killer optical illusion for you:

The "green" and "blue" spirals in this image are actually the same colour. It's like the classic same colour illusion, except, you know, colourful.

(I don't know how this illusion will affect people with one or another kind of colour-blindness. Please comment if you don't see the effect, so the rest of us can all float theories about why you're so weird and unlovable.)

After marveling at this for a while, I spent 15 minutes straightening the illusion out into parallel stripes:

Blue and green stripes optical illusion

As you can see, it still works.

If you look closely, you can see that the leftmost and rightmost "blue" vertical stripes look distinctly greener than the rest of the "blue" stripes, because they're only flanked by magenta on one side. But they still look pretty blue, despite being exactly the same colour as the "green" stripes.

There are only three colours in this image - magenta, orange and green.

(See also.)

Posted in Art, Science. 20 Comments »

The allegedly-wireless allegedly-RCA "Airnegy" alleged charger

13 January 2010 — dan

A reader writes:

You're probably getting about a million questions on this gizmo from CES, but do you think the RCA Airnegy WiFi charger is anywhere near remotely practical?

They claim it will "harvest" energy from 2.4GHz devices, like wireless phones and WiFi devices. They say it can charge a cell phone from 30% to full in 90 minutes on the CES floor, which is confusing because of all the wireless devices on the CES floor and the fact that many cell phones report full early to make their batteries look better. Since a Wi-Fi device operates at 100mW and that shrinks with the inverse-square law, wouldn't any Wi-Fi power be trivial?

Would this only be practical if you had a lot of overlapping Wi-Fi hotspots and/or a huge charger, or am I missing something? They're even claiming they can integrate this into batteries in the future.

If this is a scam or borderline useless, why is RCA promoting it? I could understand this kind of trash from a fly-by-night operation like all the fuel-pill pages, but I would think RCA would want to keep some of its reputation.

Tim

Yes, I think this has to be some sort of hoax. I ain't no RF physicist, but I don't think the numbers add up at all.

(I am, unsurprisingly, not alone.)

The output of the very small charger for my very low-powered mobile phone (a Motorola F3) is specified as 6.4V @ 200mA, which is 1.28 watts. The output of a standard Wi-Fi access point is, as you say, limited by the spec to 100 milliwatts. And, again as you say, the laws o' physics dictate that even if this thing contains a beautifully-engineered rectenna that hoovers up 90% of the 2.4GHz-ish RF energy that impinges upon it, it'll still collect far, far too little power to do anything very useful. For the same reason, it is difficult for a device the size of a canoe to harvest much energy from the wake of a passing ocean liner.

It's actually not quite as bad as you might think from a pure inverse-square law calculation, because the "impossible antennas" used in normal access points have a sort of inverse-hourglass-shaped radiation pattern, concentrating output around the antenna at the expense of output above and below it. If you're lined up with the radiation pattern of one of the larger "omnidirectional" Wi-Fi antennas, you could easily be getting three or four times as much power as you'd get if it were a real omnidirectional antenna.

But unless the Airnegy is squished right up next to the antenna so it covers, and near-totally absorbs, some relatively large fraction of the entire radiation pattern (and, of course, thereby makes devices in its "shadow" unable to see the AP any more...), then the energy it'll receive even from several out-of-specification half-watt Wi-Fi adapters will be extremely low. Never mind charging a phone - you wouldn't even be able to light an LED.

(A crystal radio can run on the RF energy from its own antenna, but that's in the microwatt range, at best.)

I suppose a device with some sort of broadband fractal antenna in it, that can suck up everything from 50Hz mains hum to high-gigahertz radar beams, might be more practical. But the Airnegy is said to be 2.4GHz-only.

Oh, and there doesn't seem to be any mention of this product on the RCA site. And although the Airnegy CES stand looks professional, the products themselves look like quick mock-ups to me. Look at this battery, for instance. It looks as if they put a construction-paper wrapper around a standard battery.

(I presume someone's paid to have the stand there, too, unless CES was having trouble filling the floor and let in hoaxers for free, like the funny fake ads that fill holes in newspaper classifieds.)

Note also that RCA is now, I think, one of those "zombie brands" that has been reduced to nothing but a logo that's slapped on random Chinese flea-market gadgets. So even if it actually is a "real RCA product", that doesn't mean much any more.

This also isn't a new idea. Here's a piece about a "prototype Nokia phone" that's supposed to somehow harvest five milliwatts from incident RF.

Can any readers who've got some of that fancy book-learnin' about that thar electrickery help me out, here?

(Somebody on that Boing Boing post busted out the Friis transmission equation.)

Has anything at all like this thing ever actually been made to work?

(And no, inductive chargers don't count!)

Posted in Electricity, Scams, Science, Strange Tales. 10 Comments »

Science Sunday

6 December 2009 — dan

Here's something that it never occurred to me to do: Using yet another thermite reaction to make metallic sodium!

(I think that technically a thermite has to be a metal powder plus a metal oxide; in the above test of the temperature tolerance of a picnic table, the experimenter is using sodium hydroxide drain cleaner, rather than sodium oxide. But it's clearly still a thermite-ish reaction.)

This is way more fun than the way I would have chosen to split the sodium out of sodium hydroxide, by merely electrolysing the molten NaOH, as Humphrey Davy did.

This technique is, of course, an eminently suitable first step into chemistry for Cub Scouts, very drunk people and trained chimpanzees. Preferably all at once.

If you'd like to make it a little less dull, try doing it in the rain!

(That whole page is pretty darn entertaining. See also "By good fortune the molten sodium hydroxide was so hot that it had vaporized the water in my skin and sloughed off without burning me chemically", from a gentleman who went on to win a Nobel Prize... but not for chemistry.)

And now, a bloke whose voice doesn't sound as if it's really meant to be that deep, using yet more molten NaOH to dissolve some glass!

In comparison, it's a positive letdown when all he does is stick his hand in liquid nitrogen...

...make potassium permanganate at home (take that, War On Some Drugs!)...

...freeze some acetone...

...or make a calcium acetate solution by reacting vinegar with antacid tablets, and then use it to gel some alcohol.

And finally, the piece on potassium (it's one louder than sodium) from the inimitable University of Nottingham Periodic Table of Videos:

Posted in Nerdery, Science. 6 Comments »

Give the (free) gift of The Secret Life of Machines!

1 December 2009 — dan

A quick update on the subject of the Secret Life of Machines series...

...which, for the information of newcomers, is

1: fantastic,
2: legal to download for free, and
3: large.

A couple of years ago, I made a torrent of a high-video-quality version of this excellent science series, which total 3.3 gigabytes.

Of late there have usually only been one or two seeds for the torrent, though, and one of them is me, and my little home DSL account can only upload at a peak speed of about 25 kilobytes per second. So it takes me a couple of days to send the whole bulk of the three series to someone (technically, it's two six-episode series of The Secret Life of Machines, plus one six-episode series of The Secret Life of The Office). And when the transfer finally completes, the recipient will then usually not bloody seed it.

So if you've still got that torrent sitting in your BitTorrent client, I'd be grateful if you force-seeded it for a while.

(A reminder for readers who're dubious about this, or protection-racketeers from one or another content company who're champing at the bit to send me a nastygram: Tim Hunkin, the creator and principal presenter of this show, wants people to download it for free. He makes this clear in many places, like for example his pages for the three series of the show. The shows are still copyrighted, but free distribution is expressly permitted.)

As I've mentioned before, you can help out with seeding even if you don't have the torrent in your BitTorrent client any more, provided you still have the files. (Which, by the way, are in the "M4V" iPhone format, are not nasty VHS rips, and are playable on all platforms; use VLC if you have problems.)

To seed if you've got the files but not the torrent, just get the torrent started as if you were going to download it again (so your BitTorrent client creates the appropriate download directory and empty files), immediately stop it again, copy the video files from wherever you've put them into the new download directory over the top of the new empty files, and then restart or "Force Re-Check" the download (depending on which BitTorrent client you have). Provided the files are the right ones for this iPhone-format version of the series, and have the right names, the download will now be 100% complete and you can force-seed it for a while.

Oh, and don't worry if your BitTorrent client says the download is only something like 99.8% complete, and it has to download a bit of data before it's "finished". That just means your computer has modified some header data in one or more of the files, so that tiny bit needs to be re-downloaded to overwrite the changes. It doesn't mean the files are corrupt.

(If you don't have a BitTorrent client at all but do have the files, perhaps because someone gave them to you on a thumb drive or something, you can also help out. You just need to install a client - µTorrent, for Windows and Mac, is excellent - and then do the starting-stopping-copying-and-then-seeding thing. The default settings for a freshly-installed BitTorrent client may stop it seeding after it's uploaded 200% of the data size of a torrent, or something; upload-ratio checking goes weird when you do the stop-copy-and-seed thing, too, because you'll have the whole download but won't have actually downloaded anything. Just right-click the torrent and select "Force Start" or "Force Seed" or whatever it's called in your client, to ignore upload limits.)

Here's a magnet link for the Secret Life of Machines torrent. (You may need to associate your BitTorrent program with magnet:... links to make this work, or manually copy and paste the link into an "Open Torrent..." dialog.)

You can also download the torrent file from isoHunt or The Pirate Bay - it was on Mininova, too, but they decided to go legit the other day and removed pretty much all of their torrents, including legal ones like this.

The BitTorrent community is moving away from .torrent files, just as it's moving away from trackers - The Pirate Bay have actually shut their trackers down altogether now. If you've got the little magnet URI for the download you want - it's ?xt=urn:btih:D62CLPSEYNRN74FRZDUC5GYVKTOOUKGE for the Secret Life of Machines torrent - then your BitTorrent client can use it to get other people who're downloading the same thing to send you the data that a .torrent file would have given you. This may take a little longer than downloading a torrent file would have, but it shouldn't actually fail unless there's nobody seeding the torrent, in which case you obviously wouldn't be able to download it anyway.

Once you've got the torrent info, the distributed hash table (DHT) system that all modern BitTorrent clients support can go on to give you the rest of the data from other users, without needing a central "tracker" system to keep everything organised.

And then, before you know it, you're watching Tim stand on the accelerator and the brake at the same time, and Rex brutalising that poor innocent refrigerator.

Tim Hunkin has done a lot of stuff since The Secret Life of Machines. Here's...

...some posh bird enjoying the latest in Tim's long and inimitable line of penny-arcade amusement machines, "Whack A Banker".

Posted in Electricity, Hacks, Nerdery, Science, Toys. 24 Comments »

Your UFO sightings for today

30 November 2009 — dan

The fewer blades a propeller - or helicopter rotor - has, the more efficient it is. (Essentially, this is because the more blades you have, the more turbulent becomes the air each blade's trying to push around. Helicopters with lots of rotor blades have so many because a rotor with fewer blades would be unmanageably large, or require a radical redesign.)

So, ridiculous though this sounds, one-bladed propellers are actually the most efficient kind. Just one blade sticking out from the hub, on one side. Like a football rattle.

I think one-bladed props have actually been used in ultra-fast control-line model planes for ages, with just a counterweight on the other side of the prop from the blade. (And yes, they do also use pulse-jets!) There's at least one swishy-looking counterweighted one-bladed ceiling fan, too.

If you want large size or high power from a one-bladed prop, though, you're out of luck, because the single blade creates unbalanced thrust that'll wear your shaft bearings away in no time. (You may also have some difficulty finding test pilots.)

The single-bladed helicopter may be coming into its own, though, now that we've got tiny, powerful jet and electric motors, and somewhat better batteries, and low-power super-lightweight computerised control systems.

All this means we can now make a one-bladed helicopter, on the "samara" or "sycamore seed" principle, except powered - it's spun by a little normal propeller, on an outrigger.

In the olden days there'd be no way for an aircraft like this, whose whole airframe spins, to do anything very useful. But nowadays... well, just look:

It's probably not even tremendously difficult to shoot video from such a thing, today. In the olden days it would have required a nicely constant rotational speed, at the very least - but now if you want to look in a particular direction, it's pretty easy to just grab a fast frame at roughly the same spot in the rotation each time. Then you rub a little cheap digital signal processing on the output, to stop it jiggling from side to side or "tearing" as the platform spins too fast for the sensor chip to grab a whole square frame.

It probably wouldn't even be hard to run a few-hundred-frame-per-second camera (or a few cheap 30fps ones) with no position detection at all, and just stitch all the video together into a 360-degree panorama, with variable frame rate in all directions, back at base.

I have this image of some game-company 3D artist trying to get a thing like this put in, as a recon tool, in a sci-fi shooter set in the year 2100, and everybody telling him it was way too crazy. I bet powered sycamore seeds will actually be dropping bugs through people's windows inside five years.

Posted in Science, Strange Tales. 6 Comments »

Ping-pong panelbeating

27 November 2009 — dan

I have just discovered how to remove dents from table-tennis balls.

We don't have a ping-pong table here, but we do have a lot of ping-pong balls, because we've got four cats and ping-pong balls are great cat toys.

When ping-pong balls are everywhere, though, you'll often tread on one, and dent it. A dented ping-pong ball is of limited utility as a cat toy, and is of course no use at all for actually playing table tennis.

As I was making tea, it occurred to me that just holding a dented ball in tongs and immersing it in very hot water might un-dent it. Even if the heat didn't soften the ball (which, as it turns out, it will), the expansion of the heated gas inside the ball ought to push the dents right out.

And I'll be darned if that is not exactly what happens. The ball swells back up to perfect roundness, and once cooled and dried it seems to bounce pretty much as well as a brand new one.

The only time this trick won't work is if there's an actual hole in the ball, which can happen if a dent has sharp creases. Then, all you get when you immerse the ball is a trail of bubbles from the hole.

(If you subsequently immerse the punctured ball in cold water, the contracting gas inside will suck the water into the ball. This lets you partially fill a ping-pong ball with liquid through a tiny hole, but you could do that with a syringe anyway. I remember seeing a documentary about controlled burning in forestry; to reliably start fires from the air, they used a machine that took ping-pong balls that'd been pre-filled with potassium permanganate, and then syringed glycerine into them, just before dropping them.)

Interestingly, ping-pong balls also smell distinctly of camphor when you take them out of the hot water. That's because they're made of celluloid, which is principally composed of nitrocellulose and camphor. This is why they burn so well:

(Some very, very cheap ping-pong balls are made of plastic instead of celluloid. They're a bit squishy, bounce about as well as a grape, and often aren't even evenly thick all over, so they wobble when rolling. Still OK as cat toys, though.)

Sadly, it would appear that I am not the first person to have thought of this repair technique. But I'm still pleased that I thought it up all by myself.

(I also invented the differential, at about the age of nine. Unfortunately, someone else had already invented that, too.)

Posted in Nerdery, Science, Strange Tales. 11 Comments »

Achieve financial independence with boiling mercury!

17 November 2009 — dan

On this blog and dansdata.com I've written about mercury, and, thanks to the very independent thinkers at Life Technology, also alchemy.

So I suppose I was just asking for this correspondence, from yesterday:

Respected Sir,

I have visited your website and then I am writing to you. so If you dont't mind then give me some opinon abuout mercury after reading below datail:

I have making mercury into solid shape in Zink and then I want to give it into golden color, I have packed it in a Copper small pots shaped " Male Female" and then put it into a ceramics Cup, then cover the Copper port with wett soil. when I heat it. after heating I made it cool and open the copper pots then I saw that due to leakage the mercury has flew up, only zink was in the pot.

I want to ask you that I want to block the leakage of copper pots so that mercury should heat and boiled but should not evaporates from the copper pots

what should i do to stop the the leakage from copper pots.

please give me some cheapest opinion. I am waiting for your good response.

Abdul

My reply:

I'm not exactly sure what you're trying to do here, but:

1. If you actually manage to seal the containers solidly, they may explode when heated. Mercury's boiling point is low enough to make this possible with relatively little heating.

2. You don't need to heat mercury much, or at all, to get it to form an amalgam with any of the many metals with which it will amalgamate. (This includes, by the way, the copper from which you are making the vessels...)

Warming the mercury over boiling water should be as much as is ever necessary, and I wouldn't even bother with that unless I'd already tried it at room temperature and it hadn't worked.

The mercury does need to directly touch the metal, though. Mercury amalgamates readily with, for instance, bare aluminium, but it will not amalgamate with ordinary zinc or copper, because of the thin layer of carbonate and oxide (respectively) on the surface of those metals. Brush the metal with a little dilute hydrochloric acid, though, and the mercury will suddenly "wet" it, and amalgamate. Metals that take a while to dissolve in mercury will dissolve faster if you chop, grind or file them into small pieces, to increase their surface area.

3. I presume you're doing this somewhere with good ventilation - preferably a standard laboratory "fume hood", but just doing it outdoors is a lot better than nothing.

You should not be doing any experiments with mercury in a poorly-ventilated area, or science will become harder and harder for you to understand, because your brain will be rotting away.

Abdul replied:

thanks for reply me. Actually I want to speak truth to you for more guidance. I belong to a poor family, and I have got a knowledge to make Gold with the combination of Zinc, Mercury with the normal temprature of Sulphur.
I have make Silver with the cmbination of Zinc and Mercury, the last Step is to Give this combination into Golden color. I have put the Prepared Silver into copper ( Male Female Pots) and then make plaster to copper with mud. then I heated the pots.

result is nearly to success but when I open the copper pots I saw there was no Mercury only burned Zinc was in the pots.

Please guide me if you can help me I will pray for you for the betterment of the world and the hereafter.

Thanks

Abdul

My reply:

Uh... do you mean you're making something that looks like gold, but isn't? You can't do that with zinc, mercury and sulphur, but there are a number of scams that're a bit like this. I'm sure, for instance, that some "alchemists" used fire-gilding, where you make a gold/mercury amalgam, rub that on what you want to gild, then boil off the mercury. That can make a lead brick look like a gold one. People have also hollowed out lead bricks and filled them with mercury, because it's a bit denser than lead and gives a fake gold brick a slightly more realistic weight.

If you think you're actually making gold, though - or have actually already made silver - then I am afraid you are mistaken.

Every possible combination of commonly-available substances under every possible combination of domestically-attainable conditions, and then some, has already been tried by alchemists, over many centuries. And all of them failed.

The alchemists didn't know why they never managed to come up with the Philosopher's Stone, but now we do; it turns out that there are very good basic physical reasons, supported by very, very large amounts of evidence including the functionality of devices which most of the world's population use every day, why turning base metals into gold is impossible.

(Well, OK, you can do it with a particle accelerator, but that requires immense amounts of electricity to make minute amounts of gold.)

Anybody who still tries to make alchemy work is like someone who declares that they don't care what astronomers say, stars really are just holes in the sky that let light through from heaven.

I feel I must repeat my warning about mercury poisoning. Alchemists who decided mercury was the key to finally making the Philosopher's Stone never made any gold, but did quite often give themselves mercury poisoning.

If you don't believe me, I suggest you take your "silver" to a precious-metals dealer and see if they want to buy it.

Abdul has not yet replied. I like to think that he's actually seeing if he really has made silver from base metals.

UPDATE: Abdul's latest, and I hope last, e-mail to me:

Respected Sir,

Thanks for reply me with kind attention.

Actually A herbal pharmacist purchased the that is called " Mercury with copper heated M aterial" at the rate of equal with gold.

My brother in law has adviced me and give me the procedure to prepare the Mercury.

I have prepared Mercury amalg with zinc but when I heat this thing in copper pots the result is opposite to his remarks.

my brother in law said that your copper pot should be leak proof so that Mercury should boiling in it but it should not evaporated or not leakage from this pot.

but I could not stop this leakage . every time all the Mercury leaked out of the copper pot when it boiled or heated.

if it is possible to stop leakage without any welding. then please guide me

I have seen that people prepare many things with Mercury then how is it possible? and how can we control Mercury and mould it in any shape or color.

I will be thankful to you.

Abdul

I told him again that these ideas are thousands of years out of date, and that we now know down to the subatomic particles why they cannot work, and that he might as well be trying to construct a ladder to the moon. I then asked him to think about why it might be that his brother-in-law is not the richest man in the world.

Perhaps it'll make some sort of impression upon him. As with this bloke who was using his twilight years to try to construct a perpetual-motion machine, I hope he finds something better to do with his life. Which could, of course, be drastically shortened if he spends a lot of time in a cloud of mercury vapour.

I wonder if there have actually been millions of people, over the millennia, who've thrown their whole life down the dry well of the Philosopher's Stone or the quest for the Fountain of Youth or perpetual motion. I suppose it'd have to be many millions, if you count all of the people whose extremely demanding religious observances leave them with little time to themselves, and few things their gods will allow them to do in their leisure time anyway. (Even if one agonising ultra-orthodox faith is actually correct, that only makes things worse for followers of all the others.)

Posted in Science, Strange Tales. 16 Comments »

APPLIED exothermia!

5 November 2009 — dan

When I finally got around to making myself some thermite, which like all right-thinking people I've been meaning to do since about the age of 10, the thing that surprised me was how bright it is. The combustion temperature of standard aluminium/iron-oxide thermite is about the same as the operating temperature of a light-bulb filament, and that's how bright the whole burning mass shines.

Here's a nice video of the process of thermite welding, which has for more than a hundred years been used to join train tracks together.

There are lots of other thermite welding videos on GooTube, though not all of them let you see the aftermath, when they remove the crucible, knock the mould sectors away and shape the still-glowing weld.

People who do this trick frequently clearly get rather blasé about it after a while, and hang around close to the crucible, or even do stuff like lighting cigarettes off the top of it. I don't think that is actually a very good idea, unless you are absolutely 100% bet-your-eyes-on-it certain that there's nothing on, or even under, the crucible that may unexpectedly flash to vapour when heated to these extreme temperatures.

Classically it's water, or even damp stone, that causes thermite to "explode", but many other substances will too. As I've mentioned before, many metals will boil at thermite temperatures, and there are all sorts of other usually-considered-inert substances that also don't play well with thermite.

Like, for instance, asbestos. The molten iron from a thermite reaction may have cooled enough to not even melt an asbestos mat, but if you put a chunk of asbestos in with the thermite, it will definitely melt and quite possibly boil.

(This ought, at least, to render the asbestos harmless. Asbestos is basically just silica in an unusual shape, so if you melt it and then allow it to cool, you get a lump of non-toxic glass.)

Posted in Nerdery, Science. 7 Comments »

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