You're never too young for thermite

In the comments of this post about chemistry sets and science education, gwdonnelly asked:

As a kid I loved playing with tools, fire, magnifying glasses, etc, etc. Along with some mates I made thermite and even had a go at some very small touch powder (could do with more practice at growing crystals there!)...

Anyway, I would like to get my kids into doing experiments in a slightly more controlled, and safe, way - any recommendations on what to get a 4-5 year old started with?

I've made this a new post so that other commenters can chime in with ideas. Here's what I managed to think of:

1: As mentioned in that post, growing crystals, including sugar crystals so you end up with rock candy:

Rock candy
(source: Flickr user futileboy)

2: A chemical garden, a quite different kind of crystal experiment often sold as "Magic Rocks".

3: While you're at it, the cheap-'n'-lazy version of a chemical garden, those little cardboard trees that grow fuzzy crystals:

Crystal tree
(Source: Flickr user drewish)

Crystal tree

(Source: Flickr user watz)

4: Go for a wander and collect and identify rocks, plants and other people's unattended property. (Strike out whichever does not apply.) You can build a collection of a wide variety of rocks you can't find in your own neighbourhood quite cheaply via eBay, too. Just bear in mind that if a mineral sample seems too good to be true, it's eminently possible that it is.

5: Tumbling your own rocks has been a popular hobby for ages, too; all sorts of ordinary-looking rocks come up lovely when highly polished:

Tumbled rocks
(Source: Flickr user vpickering)

You can make your own tumbler (or "ball mill", which is only a ball mill if you... put balls in it) from a plastic container and a scrounged-up motor. All you're likely to have to buy, besides perhaps a grab bag or two of guaranteed-impressive un-tumbled minerals, is some "tumbling media", so you can have fast abrading of rough stones and fine polishing later on without just hoping a handful of sand will do both jobs. (There are some other inexpensive tumbling-media options, too.)

6: Five years might be a bit young for soldering or an actual microcontroller (look how cheap!), but you can still play with electronics - wires, motors, batteries (and/or a jimmied PC PSU), switches (you've obviously got to have at least one knife switch)...

Breadboard wire-tangle
(Source: Flickr user LenP17)

...breadboards and jumpers and, as I've mentioned before...

LED throwie production line
(image source Flickr user c3o)

...a ton of super-cheap LEDs and other components, and surprisingly young kids can build all sorts of things.

7: Make your own thumb piano:

Thumb piano
(Source: Flickr user Trocaire)

8: Growing mustard/cress/bean sprouts on a wet paper towel...

Sprouting spud
(Source: Flickr user kidicarus222)

...or the classic toothpicked spud.

9: Magnets.

Rare-earth magnets

Rare-earth magnets are very cheap these days, and small ones make great toys for any kid old enough not to swallow them.

(And even then it's no big deal, unless they swallow more than one. This has recently turned into a problem for people who sell small rare-earth magnets as toys in the USA, because apparently you can't trust an American child under the age of 14 not to eat everything they touch. See also the American Kinder Surprise ban. Apparently something magical happens between the ages of 14 and 18, which transforms American children from Lego-eating lackwits into citizens responsible enough to be trusted with a firearm. But not a beer until they're 21, of course!)

[UPDATE: A less snarky version of the above can be found here. On reflection, I found that the tiny-toy-magnet bans now spreading across the globe are actually quite defensible.]

Do make sure you stick with small rare-earth magnets for toys. Obviously really big rare-earth magnets can crush your hand, but much smaller ones can snap together hard enough that they break. Don't get any very thin ones, and don't get anything with a diameter much more than a centimetre (half an inch, say), and their field is small enough and their momentum low enough that they'll last a long time.

If you want safe big magnets, get simple and cheap black ferrite ones instead; they're much weaker than rare-earth magnets. (It's theoretically possible to lever the big ferrite ring magnet off the back of a speaker driver, but only once have I managed to do that with a magnet of any size without cracking it.)

10: Looking at stuff under a microscope. A proper lab microscope would be best but those sell for pretty large prices, and the cheap small ones for kids are, I think, usually pretty crappy quality. Instead, you could go for one that plugs into a TV:

Eyeclops output
(Source: Flickr user Neven Mrgan)

Everybody seems to like the Eyeclops camera-microscope.

A cheap alternative is, of course, your basic magnifying glass, or a "loupe", which is either a small high-powered magnifying glass, or a monocle-style mad-scientist magnifier.

Or you could buy or make your own Leeuwenhoek glass-bead microscope:

Glass-bead microscope
(Source: Flickr user rouwkema)

(One of van Leeuwenhoek's greatest, but least helpful, achievements was concealing how easy it is to make his microscopes' tiny lenses. Everybody thought he ground them with fantastic accuracy, when all he actually did was melt the end of a glass rod and allow surface tension to pull it into a sphere.)

Leeuwenhoek microscopes aren't the easiest to look through, but can effortlessly resolve the tiny beasties in pond water.

Oh, and then there's the quickest microscope ever, provided you have a digital camera with a very small lens, like the camera in a phone: Just put a drop of water on the lens, turn the phone over carefully...

Water-drop phone-camera microscope
(Source: Flickr user ipasha)

...and bingo, one microscope!

OK, folks; what have I missed?

More knives and stabbing weapons

A reader writes:

I have little background knowledge of knives and even less experience with sharpening. I recently did some googling of your older articles to learn a bit more about these topics.

[Except for the Miyabi 613 review I put up the other day...

Big eff-off shiny knife

...and this piece, I haven't actually written much about knives and sharpening. These three reviews don't really talk about it. -Dan]

I'm in the market for some solid kitchen knives. It looks like buying some used Global knives on eBay might be a good way to get some high quality steel. I would likely purchase the CRKT Slide Sharp (based on your recommendation) and attempt to learn to sharpen. The other possibility is a ceramic knife, since these kitchen knives shouldn't ever be prone to "abuse". Which would you recommend?

More interestingly, though, I'm looking to purchase an every-day-carry foldable knife for my Dad. He has a long history of buying $20 pocket knives and shortly destroying them. He uses them to pry, chisel, stab, cut, and occasionally as a makeshift screwdriver. I've done some brief research on the topic and heard some names like "Strider" tossed around. I'm OK with spending some decent money to get a knife that will withstand this sort of abuse (and ideally have a warranty of some type). What would you recommend in this situation?


Yes, used famous-brand kitchen knives are a good idea, provided they haven't already been sharpened down to nothing, or hideously abused. (See also, old cast-iron pots and pans. Very tough, and quite non-stick too, when properly seasoned.)

If you're going to be using the knives a lot then you might want to try a few different types, though. Not only are there umpteen blade styles, but some people prefer Global's unusual seamless ovoid handles, some like traditional Western handles that're a riveted sandwich with a full tang in the middle, and some people prefer the circular traditional Japanese handles.

If you're buying used knives that you're probably going to have to sharpen before you use them, though, you should practice on a cheap knife or three before assaulting a nice one. Yes, it is possible for a complete amateur to to screw up even when using a guide jig, and the faster a given sharpening system works, the faster you can screw up.

The Slide Sharp jig is pretty close to foolproof, but because it's based on ceramic "crock sticks", it's no good for sharpening a really blunt blade. It'll do it eventually, but it's much better to start with a cheap coarse stone to put something approximating an edge on the blade.

So go to the dollar store and get yourself a cheap coarse stone or some suspiciously cheap alleged diamond cards, and the cheapest knives they've got that are actually physically functional. This mainly just means the knives need to have a a proper tang - steel extending from the blade - down the middle of the handle, not just some dinky glue joint; I don't know what the cheapie-stores are like where you live, but the one in my town doesn't have any really worthless knives. You'll probably find Western-style kitchen knives in a discount store, and quite often also small knives and cleavers using the single-sided Japanese chisel grind.

The only thing really wrong with super-cheap knives, provided they have a proper tang, is that they'll go blunt faster than a fancy knife. But that means they're faster to sharpen, too, and it also means you can just chuck them in the dishwasher and not worry about them maybe bouncing against a glass and denting the edge. "Oh no, my two-dollar knife is dented."

(Update: To make sure the above claims remain true of, at least, my local Go-Lo, I just bought a boning knife with a six-inch blade there, for $AU2.49. Full tang, good handle, and a good factory edge everywhere but on the tip, which is a common problem for cheap knives and easily remedied. All in all a perfectly satisfactory piece of cutlery even without touching up the tip, for marginally more than the price of a McDonald's cheeseburger.

Update 2: After about a year of use and numerous trips through the dishwasher, it's become apparent that the "rivets" holding the handle onto this super-cheap knife are just disks of metal glued onto the side of the handle. One has fallen off. So there's glue holding the handle and blade together, instead of real rivets, but it's still holding on fine. It'd be easy to re-attach the handle "scales" to the sides of the blade if they ever do come loose. Here's an illustrated article about the handle of a knife with real rivets, in case you're wondering what I'm talking about.

There were four-knife sets there too, including a full-sized carving knife, for less than $AU10. If I were a penniless student kitting out the share-house kitchen, I'd just get those knives and one cheap sharpening stone; job done, for a third of the price of one Wüsthof paring knife.)

You can get off-brand knives of decent quality quite cheaply, too. I like the ones Aldi supermarkets sometimes sell along with their other limited-time loss-leader products; their santoku-type knives have a good thin profile and those little hollows in the sides of the blade to stop sliced food sticking to the knife, and you can get a small one and a medium one for less than $US10. You may be able to find similar bargains in kitchen-gear or department stores, if the salespeople don't manage to steer you towards higher-margin European brands.

If you sprinkle a few carefully-chosen search terms on eBay, you can find quite a few decent-looking and cheap kitchen knives there, too.

Ceramic knives can now be had cheaply from the usual crapvendors (and Aldi!). I don't know how good the edge is on the off-brand ones, though, and they're basically unsharpenable even with diamond abrasive (you have to send the brand-name ones back to the factory for re-sharpening). So if you get a bad one it's going to stay bad forever. But if you get a decent one and don't use it to pry the lids off paint cans, in domestic use it'll probably last you many years. (I wouldn't be surprised if advanced materials, over the next decade or three, made knife-sharpening a thing of the past.)

I actively enjoy keeping steel knives sharp, so I haven't bothered to buy any ceramic ones. The only ceramic blade in this house is the one on my Kyocera scraper, which is an interesting tool; the ultra-hard blade hasn't visibly worn in years of use, and you can use it to scrape just about anything off just about anything else. If I were buying ceramic knives, I'd just start with the best-reviewed ones on DealExtreme or whereever. There are some pretty cheap ones on Amazon, too. (Note that the brightly-coloured super-cheap Komachi knives are actually steel with a low-friction plastic coating, not ceramic.)

The one other piece of advice I have for the kitchen-knife novice - not that I'm very far above novice status myself - is that you should never use a sharp knife on a glass cutting board, ceramic plate or stone tabletop. Cutting on a metal surface isn't a great idea, either. Glass cutting boards are wonderfully hygienic, and they're fine for cutting cheese on with a blunt knife, and they're also OK for the average domestic chef, because the average domestic chef has nothing but blunt knives anyway. Glass cutting boards might even be all right with ceramic knives, though I doubt it. They'll definitely instantly fold over the edge of a sharp steel knife, though. Use wooden or plastic cutting boards instead; plastic is the more hygienic.

On to the subject of your knife-torturing father.

No folding knife can be anything like as strong as a fixed-blade knife for levering and prying and such. Some fancy folders are a lot stronger than you'd expect, but it's just not possible to make a hinge that's as tough as a piece of solid metal.

(If you're in an emergency situation and have to pry something with a folding knife, then you'll often be successful; usually the blade will break before the pivot does. There's a good chance you'll ruin the pivot before anything actually breaks, though, so your folder won't fold any more.)

That said, there are indeed quite a few surprisingly tough folders. Kershaw's "Zero Tolerance" line, for instance, pretty much won't break unless you're really actively trying to break them:

The street price for the knives in that video is pretty high, though. Alleged "Zero Tolerance" knives go quite cheaply on eBay; I suspect most of them are knockoffs.

That's not necessarily a disaster, though. Just because the steel's cheaper and the machining's less precise doesn't mean a knife will be easy to break. The only knockoff knives I'm really leery about are liner-locks and their relatives the frame locks. These must be made precisely, with hard steel in the right places, or they may close on your hand during a push-cut.

(If in doubt, open the knife, turn it over and, with your fingers out of the closing path of the blade, smack the back of the blade sharply on the edge of a table. A lousy liner- or frame-lock knife, or a good one that's old and badly worn, will close when you do this.)

The "Strider" brand you mention is known for making very beefy knives that're probably about as strong... a folder that fits in a pocket can possibly be (you name it, and someone on YouTube will be obsessing over it!), but I don't know anything more about them than that. Strider also make fixed-blades, which is really what you've got to get if you want to get as close as possible to indestructibility. Umpteen companies make different versions of the single-edged fixed-blade "combat knife"; a small one of those would suit your dad, if he doesn't have to have a folder.

If he must have a folder, I'm torn between suggesting some expensive chunky US-made "tactical" folder that preferably didn't hit too many branches when it fell out of the Mall Ninja tree, or just a hatful of cheap Chinese folders. Abuse will kill any folding knife eventually; if it only cost eight dollars in the first place, though, who cares?

You can also get cheap Chinese knockoffs of every oddball folding-knife innovation, which is a cheap way to make a fun little collection of things that'll make you bleed when you play with them while drunk.

(A gold-medal example of this is knockoffs of the Kershaw External Toggle, most of which copy the entertaining mechanism very well, but are smaller than the real thing. Here's one that isn't too tiny. There's a simple, safe way to open and close this sort of knife, and a flashy, dangerous way involving flicking the protruding lever with your thumb. The smaller the E.T. clone, the more it hungers to bisect your thumbnail.)

Columbia River Knife and Tool, makers of the abovementioned Slide Sharp kit, are known for their range of folding knives that open and close in peculiar ways. My own everyday pocket knife is a CRKT Rollock (now discontinued). Like many novelty folders, the Rollock doesn't really work any better than a normal folding knife - actually, it's slightly prone to close unexpectedly, or try to open in your pocket, and it's definitely not going to win any abuse-tolerance prizes. But it's cool, with no mall-ninja ballistic carbon-fibre tactical BS.

If you find something on eBay that's described as a CRKT or Spyderco or Strider or some other big-brand knife, and looks just like it, but costs a fifth as much, it's a knockoff. Some knockoffs are crap, many - often the ones that don't try to look exactly like a given big-brand knife - look and feel fine, and some are almost indistinguishable from the real thing.

I review an excellent example from the obviously-a-knockoff category, here; it shares only its general shape with the Boker original, and is an excellent tool for the money. I also once bought a couple of knockoff CRKT Glide Locks on eBay. They look exactly like the real thing, but one of them fell apart in a week.

It also occurs to me that a person who keeps abusing a knife by using it as some other kind of tool could, perhaps, be in the market for a multi-tool. I think the toughest of the Leatherman/Gerber-type plier-multitools is the SOG PowerLock, and there are of course many others. SOG also just released the PowerDuo, a plier-type tool with a full-size knife blade.

If you want the knife to be the main tool with other stuff less important, then a hollow-handled fixed-blade "survival knife" could be a good idea. The hollow handle doesn't have to have matches and tinder and fishing line in it, after all; you can pack other tools, like a real screwdriver for instance, in there.

The overwhelming majority of hollow-handle knives are garbage, because they have no tang to speak of and just glue connecting the blade to the handle. Until recently the only good options in this field were expensive models forged out of one piece of steel, but now the overgrown teenagers at Cold Steel have made the Survival Edge, which is big enough to be useful without being so large that it's a ridiculous Rambo knife, and whose plastic handle is moulded around the short tang of the knife.

The plastic-handle idea still sounds as if it'd be breakable, but...

...that does not seem to be the case. It's the thick end of fifty US bucks delivered, but comes with a polymer sheath and sharpening doodad, and if the above video can be believed, will probably last approximately forever.

The Survival Edge is also new enough that none of the ones on eBay should be knockoffs.


Count The Errors, chemistry edition

There's a BBC News piece called "Whatever happened to kids' chemistry sets?", which makes the same point that many people have before, that zero-tolerance for any possible risk to children does not actually do those children any favours. It's hard to gain anything without at least exposing yourself to the possibility of pain; kids should be able to learn and have fun in ways that are at least a little dangerous.

You know the drill, though. Playgrounds, unsupervised play in general, chemistry sets; all neutered in the name of safety. For some reason many kids are still allowed to ride a bicycle, but heaven forfend you give your ten-year-old a pocket knife.

The video at the top of the BBC piece...

Get Adobe Flash player

...shows some experiments you can't do with modern kits. These experiments are as un-dangerous as they look.

The classic potassium-permanganate-plus-glycerol fire reaction (with some glucose added to provide additional fuel) does not have to be done in a fume hood. Just doing it outdoors and not deliberately inhaling the smoke will do.

You can still get the ingredients for that one quite easily, too. Glycerine and glucose powder are in many supermarkets, and potassium permanganate is still used as a disinfectant and general-purpose purifier of anything that benefits from being exposed to a moderately strong (by sane people's standards) oxidiser. So it's probably not illegal to send it through the post where you live (though there may be some ridiculous restriction having to do with drugs), and there are plenty of people selling it on eBay. (Check the Readily Available Chemicals lists, if you find yourself unable to locate some reagent or other. )

The only other old-chemistry-set "experiment" in the above video is even less alarming, simple flame tests. Again, salts that create brightly coloured flames or sparks aren't very hard to find; the one stop shop for them is a firework-supplies place, and you shouldn't need any fancy licenses or expensive special shipping to get them, since they're just the stuff that colours the fireworks, not the stuff that makes fireworks go bang. (And, again, Readily Available Chemicals can help.)

Oh, and that bit at the very end of the video with the squeaky test-tube sounds just like lighting hydrogen, which you can easily make electrolytically. But the tube seemed to be mouth-upwards, so it may have been some other flammable gas.

So the video's a bit boring, but OK. The actual BBC article, though, contains several mistakes.

The author says, for instance, "some chemistry sets of bygone ages even offered instructions and materials to be able to blow glass at high temperatures".

Well, yeah, of course they did. Making your own simple glassware - which pretty much only means bending and stretching tubes, not much in the way of actual "blowing" - is not particularly dangerous. You can do it on a kitchen gas stove if a proper burner is not available. Just stretching a glass tube lets you make very fine dropper nozzles; add some commercial flasks and beakers, some stoppers and a cork borer, and you can make a reasonably effective condenser, with a wet cloth and a fan standing in for the proper water jacket.

"Rosie Cook, assistant curator at the Chemical Heritage Foundation", is quoted as saying "You are letting a 12-year-old blow glass, there was uranium dust with a stereoscope where you could see the radiation waves..."

Bending glass tubes is not a task for toddlers, but any 12-year-old who cannot be trusted to do this is a 12-year-old who should also not be allowed to make themselves a sandwich. OK, the dangerous part of a bread knife is easier to tell from the safe part than is the case with glass (the First Law of the Laboratory: Hot glass looks exactly the same as cold glass), but this is no reason to presume that a 12-year-old has no more sense than a toddler.

And as for the "uranium dust" part... oh, man.

First, if any chemistry set ever came with actual uranium dust, I'll eat a whole shop full of hats. What chemistry sets came with was some bits of uranium ore or, at the very most, yellowcake.

And they didn't come with a "stereoscope"; you can't view ionising radiation with a View-Master. They came with a spinthariscope. (Perhaps the original piece as written had this right, but a sub-editor helpfully "corrected" it.)

That's a simulation, via Theo Gray, of what a spinthariscope looks like to a dark-adapted eye. (Actual video of the very dim twinkly lights tends to look rather underwhelming.)

And the "radiation waves" thing is a mess, too. I think you can see wave/particle gamma photons with some kinds of spinthariscope, but I'm pretty sure the chemistry-set ones - which you can still buy today - only respond to the alpha and maybe beta particles that decaying uranium and its daughter products emit on their way down the line to lead.

And then there's a neat-o little table at the middle of the BBC article, listing the interesting ingredients chemistry sets used to have and why they don't have them any more:

Chemistry sets of old

Chemical Why was it included? Dangers
Uranium dust It was "unofficially encouraged by the government", said chemistry set creator AC Gilbert, to help public understanding of
atomic energy
Radiation exposure is today strictly controlled due to wide range of
damaging health effects including risk of cancer
Potassium nitrate Combined with sulphur and charcoal to create gunpowder Can be used to make a fertiliser bomb
Lead acetate Used as a dyeing agent Toxic when eaten, as are many other lead compounds. Blamed for death of Pope Clement II in 1047
Ammonium carbonate Used in coloured fountain experiment where solution turned from red to blue The main component of some smelling salts, it can be dangerous if used in high doses regularly
Sodium hydroxide Used in colour-changing experiment Burns skin on contact

It says the intended purpose for potassium nitrate in chemistry sets was to make gunpowder, but it's not there any more because you can also use it to make a "fertiliser bomb":

Well, yeah, I suppose potassium nitrate could technically count as a fertiliser-bomb component, but I think they've actually confused it with ammonium nitrate. "Can be used to make gunpowder" would be a perfectly good thing to put in both the "original purpose" and "why it's no longer available" columns.

(I also love how the table lists one of the "dangers" of lead acetate as "Blamed for death of Pope Clement II in 1047". I don't think that fact actually played a major role in the thought process that led to the removal of lead salts from chemistry sets.)

And the only "why was it included" reason for sodium hydroxide was "used in colour-changing experiment".

That was it, huh? That's all it's good for? That's the sole purpose for a strong base? Makes you wonder why it was in there in the first place, doesn't it?!

It really does look as if nobody who had anything to do with the creation of the BBC article knew what they were talking about.

I found the BBC piece via this Boing Boing post by Maggie Koerth-Baker, which discusses the BBC article but does not dissect it. I suppose this proves the point; even Maggie, excited about science even by Boing Boing's standards, didn't notice the glaring errors. Perhaps I wouldn't have, either, if I hadn't spent a lot of childhood hours in the little workshop/laundry melting, boiling, reacting and distilling things.

And, of course, setting stuff on fire, more than once with the permanganate/glycerol reaction.

Among other things, I discovered that zinc burns with a pretty blue flame, and produces copious white fly-ash:

I never burned enough of it to get sick, though.

Making "plastic sulfur", a rubbery polymeric pseudo-allotrope that's the initial form of quenched molten sulfur, was also fun:

But smelly.

And yes, a kid can do this, in the kitchen, with very little chance of winding up dead:

(I'd also like to rehabilitate mercury's image. It seems almost nobody these days knows the difference between organomercury compounds - which are very very poisonous - and metallic mercury, which isn't good for you, but which is not actually very dangerous.)

I did the iron-and-sulfur reaction, too:

You can even get away with making nitrogen triiodide...

...if you make a respectfully minuscule amount, and wear eye protection. Which should be your habit when doing anything with chemicals or power tools, for the same reason that it's sensible to train yourself to use your indicators, by reflex, while driving. Yes, that does mean you'll occasionally feel silly because you indicated for, say, a turn in a road that isn't actually any kind of intersection. But it's better to indicate when you don't need to, and wear eye protection when reacting vinegar and baking soda, than to forget to indicate when it does matter or leave the goggles off when playing with explosives.

I didn't make thermite...

...until I was a grown-up, but I now champion that as an excellent experiment for kids, too.

Actually setting the thermite off definitely requires adult or responsible-teenager supervision, but the components of standard iron-oxide/aluminium thermite are quite inert and non-toxic (again, the kids should wear eye protection while mixing the ingredients, even though it isn't really needed), and the mixture won't light without a high-temperature fuse - a sparkler or magnesium ribbon. So small children can mix up thermite all by themselves, quite safely. And they should.

(One caveat: If they mix anything else into the thermite, especially water, then it will flash to vapour when the thermite burns and throw blazing thermite all over the place. This shouldn't matter unless you're setting the thermite off in an unsuitable location - q.v. - or standing unwisely close, though. You also don't need to panic about one drop of water or a couple of hairs in the thermite; it's not that touchy.)

If chemistry sets and, increasingly, schools no longer provide any real hands-on experience with chemistry, parents and kids themselves need to step up and do it, even if all you do is grow some crystals.

There's a lot of fun, and entertainment, to be had in the wide area between the kindergarten-science of dumbed-down chemistry sets and the truly hazardous experiments that, for instance, produce copious amounts of highly poisonous fumes, or have reaction products that are illegal to throw away.

Teaching kids that "chemicals" are dangerous is as stupid as teaching them that all drugs are equally, and enormously, bad. You let 'em ride a bike; you should also let 'em make some stinks and bangs.

On hobbies, and countries

A while ago, I figured out why it is that Top Gear hate caravans.

It's not just because being stuck in a four-mile tail-back behind a Morris Oxford towing a 1986 Chateau La Car is even more frustrating when you're attempting to review a 900-horsepower quad-turbo Lamborghini Testicoli Enormi. It's also because Top Gear are in the UK, and I think caravanning in the UK is like metal-detector-ing in Australia.

There are few places in the UK that are worth dragging a little mobile house to. Cornwall's nice enough, but it has hotels, as do the other parts of the UK that try with varying plausibility to present themselves as holiday destinations.

OK, maybe you enjoy being able to have a fry-up breakfast out of the rain and then tramp around a different soggy piece of Scotland every couple of days. But this is stretching it.

Here in Australia, on the other hand, we have large amounts of beach and forest and low-but-wide mountain ranges that are not within convenient distance of a motel. You can easily spend a year driving around this place and still have failed to come within a hundred kilometres of enough land area to make up what most people call a country. OK, a signficant amount of that area is one of our many great expanses of nothing much...

Gunbarrel Highway

...but there's still a lot of Australia out there.

The whole area of the United Kingdom, plus southern Ireland, is about 314,000 square kilometres. That's a little less than the two smallest Australian States, Victoria and Tasmania, put together.

The whole of Australia has an area of more than 7.6 million square kilometres. But Australia's population is less than 23 million, versus 62 million and change for the UK. (Australia's population is about 15% more than that of New York state.) And most of the Australian population is crammed into little strips on the coast.

Result: An awful lot of wilderness where you could play with a howitzer for weeks without hitting anyone. If you're crossing those distances, a little towed house can be convenient.

If you make a hobby out of metal-detecting in Australia, though, you're not likely to find anything very interesting. Humans have been here for tens of thousands of years, but until Europeans showed up and commenced doing what they usually do, the indigenous Australians didn't have any metal at all.

You can find plenty of stuff if you swing a metal detector around in any vaguely habitable part of Australia, but the most antiquitous items you're likely to locate are ring-pulls.

Oh, and you're not going to find any gold, either. There are still plenty of places in Australia where you can pan for gold successfully - which is to say, at the end of the day you'll have a clearly visible collection of gold-specks in a little vial, which may be worth as much as fifty cents. But our most recent gold rush was well over a century ago. You're more likely to find a fist-sized meteorite than you are to find a gold nugget, and you are not likely to find a fist-sized meteorite.

If you live in the UK, on the other hand, then just going into your back garden and digging a hole will very probably find you some Roman pottery, or even coins. The pottery will probably be worthless broken shards and the coins will probably be equally worthless lumps of corroded bronze, but they'll still be more than a thousand years old.

If Tony Robinson et al came to Australia to dig places up, they might be able to find something a couple of hundred years old in Sydney, or perhaps an interesting geological specimen out in the sticks, but that's about it.

Am I missing something, here? I invite comments from any Britons who gain deep fulfilment from caravanning the Grampians, or Australians who metal-detected a gold bar on Coogee Beach.

Posted in Cars, Toys. 14 Comments »

It explodes, at the speed of plot.

A reader writes:

My name is Adrian and I had a question for you and your fancy calculations:

What would happen if you cut an atomic bomb (or any variant of nuclear bomb) in half with a lightsaber, as that bomb was heading toward the ground? My guess is you would disable the detonator but would probably set off the plastic explosive contained within, yet still not detonating the bomb.


This rather depends on what a lightsaber actually is, and what it does. Which is hard to pin down.

Like various other aspects of the Star Wars universe, lightsabers don't really make a lot of sense. The blade apparently weighs nothing but has some air resistance (making a cardboard tube a most effective surrogate!) and, by canon, a strong gyroscopic effect. But that effect is hard to see when, for instance, Luke first twirls his father's lightsaber around in Ben Kenobi's hut. There's a notable absence of precession causing the blade to swing weirdly...

...and cut up Luke, or Ben, or at the very least some of Ben's furniture.

If you need to cut through huge metal doors on a Trade Federation ship it apparently takes a lightsaber a while to do it, but the armour of a seismic tank... rather weaker.

The more you think about this stuff, the less sense it makes. If the damn blade doesn't weigh anything, for instance, why not just do whatever's necessary to make a saber with a really long blade, then point said blade at your enemy, and invite him to impale himself upon it at his leisure? A Jedi asks not these obvious questions, nor does one wonder what the heck people were thinking when they made canonical lightsaber-ish weapons that are clearly more likely to kill the user than their enemy. (See also.)

Oh, and lightsaber blades seem to bind together when they touch, which is what you'd bleeding want to happen when you're fighting with swords that have, in almost all cases, no hand-guard of any kind.

The original lightsaber props had a real gyroscopic effect, because the blade was a spinning stick covered with retroreflective material. You can see and hear one of them in action at the beginning of this blooper reel:

This was originally hoped to provide an adequate lightsaber effect all by itself when illuminated by a light mounted next to the camera lens, for the same reason why retroreflective road signs glow when illuminated by headlights, which are relatively close, angularly, to the eyes of a driver. (If you're on foot and illuminate such a sign with a flashlight held next to your head or, better yet, right between your eyes, the sign will glow surprisingly brightly, on account of the near-perfect angular alignment of the illumination and your eyes.)

The reflective saber effect didn't actually work very well, though, so the sabers were dressed up further in post-production. This left a few telltale signs in the original versions of the early Star Wars movies, especially A New Hope. Before Lucas started "improving" that movie, a saber pointed straight at the camera pretty much disappeared. See also the variable-length, "dual-phase", lightsaber, which was invented to explain why the special effects for Vader's schwartz didn't make it the same length in every shot.

Oh, and lightsabers also tend to be used by telekinetic wizards who can predict the immediate future, so all the arrant Flynning you see lightsaber fighters doing (apparently trying to hit the enemy's sword, not the enemy himself...) is of course entirely explained by... tech tech tech.

Lightsabers seem to be able to cleave through most things instantly (there are several lightsaber-Kryptonite substances in the Star Wars universe to make this less of a problem for storytelling, a la the widely-used sci-fi convention that faster-than-light drives don't work if you're too close to a planet or star, so goodies and baddies can't effortlessly evade each other all the time). The material that was in the kerf of a lightsaber's cut just seems to... disappear. If the blade were actually the stick of ultra-hot plasma that it's meant to be, it'd create a strong wind of superheated air just sitting there stationary making its cool noise, and there'd be a serious explosion whenever you hit anything solid with it, blasting some of that solid into gas at the very least, and possibly more plasma. But nope, doesn't happen. Lightsaber-cut matter just vanishes.

Heck, lightsabers don't even seem to cast any light, a lot of the time. You can see them with your eyes, but no photons from them seem to encounter anything but the audience's eyes. This was of course also a special-effects limitation; the original lightsaber effect was just painting on the film frames, and painting realistic illumination of other objects by the lightsabers was too hard. When it isn't too hard to depict, lightsabers light stuff up just fine.

All of these niggles are, of course, not important. Nobody's pretending Star Wars is even slightly hard sci-fi, so sound in space, and crappy Stormtrooper marksmanship, and ray-guns that shoot beams that travel much slower than bullets, and magic laser swords, are all perfectly acceptable space-opera components. The only time this stuff annoys me is when someone creates yet another of those awful The Science Of Star Wars or Star Trek or Probably Even Bleeding Doctor Who By Now books or TV shows.

[Update: Oh, for fuck's sake...]

The idea always seems to be to trick students who don't like science into learning something, but the result always looks to me like the Lego kits for kids who don't like Lego. This idea is a fundamentally bad one, even if you do manage to wring some actual scientific relevance out of Star Wars, which is about as easy as wringing it out of Jack and the Beanstalk.

If you actually apply something resembling real science to lightsabers, you get a weapon that kills everyone in the building if you ever hit anything with it.

Here's a much more important example of the hopelessness of this The Science Of Some Fantasy Show idea, which arises whenever you try to apply real science to any space-opera scenario that has faster-than-light travel:

If you've got FTL travel, in a universe subject to relativity, you can now also travel into the past.

Absolutely definitely, no question about it. Doesn't matter if you use hyperspace or a warp bubble or teleportation or jump-gates left by ancient aliens. FTL plus relativity equals time travel.

The usual way to get around this is to subject your fictional universe to an Acme Hydraulic Universe-Flattener and explicitly or implicitly erase relativity entirely. You pretty much have to do this to have FTL in the first place, so it's not that much of a loss.

The only other way out is to boldly declare that the same future technology that created the FTL drive also proved Einstein Was Wrong. Saying that, in the face of the large amount of experimental and practical evidence that both general and special relativity are, in our universe, real, is about as plausible as a physicist today saying Newton Was Wrong.

(Newtonian physics is wrong when speeds, mass and/or time values are very large, but relativity refines Newtonian physics, it doesn't overturn it. Space-opera FTL technology can only plausibly overturn relativity with the help of godlike entities, the discovery that we live in a simulated universe with variable rules, or some similarly cheap trick. Otherwise you might as well be saying that new discoveries have revealed that four is prime.)

A significant amount of modern literary space-opera acknowledges the FTL-equals-time-travel problem, but time travel only happens occasionally in shows and movies whose names start with "Star", and it's usually a great surprise to the cast when it does. (And an even greater one, to the characters at least, when they travel from the future back into the same year, and usually the same city, when the show was actually filmed.)

This is all just a teeny bit of a long walk to my answer to "what would happen if you chopped a nuke in half with a lightsaber?", but I hope it explains why my answer is "damned if I know, but the special effects would be good, and the acting lousy".

Psycho Science is a regular feature here. Ask me your science questions, and I'll answer them. Probably.

And then commenters will, I hope, correct at least the most obvious flaws in my answer.

Further fizzing

A reader writes:

After reading your post about vinegar and bicarbonate of soda as cleaners, I've been using bicarb more to clean and deodorize things (a bicarb and water paste is pretty good for spills on fabrics and carpets - just massage it in then leave it overnight and vacuum it up the next day. Clogs the vacuum filter something fierce, though).

In the course of my experiments, I've found that if you add bicarb to near-boiling water, it fizzes. This is with plain water fresh out of the electric kettle, not water plus vinegar or anything else acidic. Add bicarb to the water, it fizzes and dissolves. Add more bicarb, more fizz. Add more hot WATER to the existing bicarb-and-water solution, and it fizzes again!

What's going on, here? I know dissolving stuff in water can change the boiling point, but I think it usually INCREASES it, and the difference isn't usually very large. Is the bicarb providing nucleation sites for boiling? Why's it still happen when the bicarb's dissolved, though? And how can it boil water that's not hot enough to boil naturally any more?


The Wikipedia article actually explains this; above 70 °C, sodium bicarbonate and various other bicarbonates decompose. In sodium bicarbonate's case, it goes from NaHCO3 to sodium carbonate (Na2CO3), water and carbon dioxide. The hotter it is, the faster this happens, and it happens in solution too.

So the fizz is still carbon dioxide bubbles, just as if you'd added bicarb to vinegar, but the source of the CO2 bubbles is different.

Psycho Science is a regular feature here. Ask me your science questions, and I'll answer them. Probably.

And then commenters will, I hope, correct at least the most obvious flaws in my answer.

Megatons and milligrams

A reader writes:

In one of Alastair Reynolds' books, someone sets off a "pinhead-sized" antimatter bomb, and it explodes with a yield of about two kilotons of TNT. Is that accurate? Would you really only need that much?


I think you're talking about Revelation Space, the first book in that series, written slightly before Futurama debuted and so forgivable for its inclusion of a captain named Brannigan.

First, note that in a matter-antimatter explosion, you're not just converting the mass of the antimatter into energy. You're also converting an equal mass of matter, because if that matter was not around there'd be no annihilation and no explosion.

The energy yield of matter annihilation is a simple case of mass-energy equivalence, and thus subject to the famous e equals mc squared. Which is to say, energy in joules equals the mass being annihilated in kilograms times the square of the speed of light in metres per second.

The dominant number there is obviously c-squared; the speed of light in vacuum is 299,792,458m/s, and squaring that gives you 89,875,517,873,681,800. Or, in less-cumbersome scientific notation about 8.99E+16 - 8.99 times ten to the power of 16.

"TNT equivalent" bomb-yield numbers are tightly defined, too; one ton of TNT is defined as 4.184 gigajoules.

Now, what's a pinhead weigh?

I just grabbed some ordinary one-inch dressmakers' pins and found there were about fifteen whole pins to the gram. I'm not about to snip off enough pinheads to get them to add up to the minimum resolution of my triple-beam balance, but I'd guess the mass of these pins' heads to be ten milligrams, at most.

Fortunately, the mass of the Revelation Space bomb is mentioned in the book; it's described as containing "only a twentieth of a gramme of antilithium". That's fifty milligrams, but that doesn't sound like a crazy weight for the head of a stouter pin than the ones I weighed.

Plugging fifty milligrams, 0.00005 kilograms, into e=mc^2 gives

e = 0.00005 * c^2

= 4.49378E+12 joules

= 4494 gigajoules

...which at 4.184 gigajoules per ton of TNT, adds up to 1.074 kilotons. Double that to take into account the matter that's annihilating with the antimatter, and you get 2.148 kilotons. Which is indeed close enough to two kilotons for horseshoes, hand grenades and tactical nuclear weapons.

The biggest thermonuclear explosion ever created by humans, the immense and impractical Soviet "Tsar Bomba", had a possible yield of about 100 megatons, but was dialled down to 50. 50 megatons at 4.184 gigajoules per ton is 2.092E+17 joules. Turning e=mc^2 around to solve for mass, m = e/c^2, gives:

m = 2.092E+17 / c^2

= 2.33 kilograms of matter converted into energy, for the biggest bomb we've ever made, and possibly the biggest bomb we ever will make.

Around the weight of a healthy adult chihuahua.

(See also solid blocks of electrons, which knock antimatter energy density into a cocked hat and which may be a technology within the reach of some entities in the Revelation Space universe. Oh, and see also, also, the fun you could have whacking lumps of plutonium together by hand.)

Psycho Science is a regular feature here. Ask me your science questions, and I'll answer them. Probably.

And then commenters will, I hope, correct at least the most obvious flaws in my answer.

"Small boy on bridge, this is Ghost Rider requesting a flyby..."

Some more of my friend Mark's FPV quadcopter, this time buzzing around Brisbane, where he lives.

(The funny-looking tower is the Skyneedle.)