Fins! Fins, everywhere!

An update to yesterday's post about the "Gaspods" fuel-saving vortex fins for cars:

Until I read jaypeabey's comment pointing to a series of articles on the AutoSpeed blog, I had no idea that a bunch of commercial products similar to GasPods already exist, and that they're well-known in aeronautical applications, too.

Fuelsavers vortex generator

These are "VG Fuelsavers", "As Seen On the ABC's 'NEW INVENTORS'"! (That's not necessarily a point in your favour, guys.)

VG Fuelsavers appeared on The New Inventors in 2006. AutoSpeed contacted the Fuelsavers people shortly after that, and offered to actually, you know, test them, which The New Inventors doesn't do.

This offer was, silently and mysteriously, rebuffed.

The Fuelsavers site claims a "6% to 9%" reduction in fuel consumption", which is plausible, if you do almost nothing but highway driving.

Even a 6% gain for a car mainly driven in city traffic, though, does not seem likely to me. Even at highway speeds it's difficult for a drag-reducing aerodynamic modification to give a fuel-economy gain of more than about 60% of the drag reduction. Since drag increases with the square of speed, aerodynamics are very important to racing cars, and moderately important for highway driving, but almost irrelevant at low speeds. (This explains why you don't see a lot of aerodynamically-designed bulldozers.)

Airtab vortex generator

Airtab vortex generators

These ones are called "Airtabs". They may be the first gizmo I've ever seen that claims some connection with NASA, and is actually telling the truth. (See this, for instance, for the usual situation. Or this, for the similarly-common military version. Some people, though, will believe anything.)

AutoSpeed tested the Airtabs, but not very well. The test wasn't blinded or well-controlled, and the only test vehicle they actually measured fuel consumption on was a Honda Insight. If it was the first-generation model, then it started out with a coefficient of drag of only 0.25. That's about as good as production cars have ever managed, so it's arguable that it can't be improved very much more, and certainly not by just sticking on some little fins.

To be fair, a facility that can do proper drive-cycle tests probably can't do them on aerodynamic devices, because drive-cycle tests are usually done on a stationary dynamometer. You need a wind-tunnel to test aerodynamics thoroughly, and they're a lot rarer than dynos.

But, as AutoSpeed points out in their first article about vortex gizmoes, you can get a good idea of the structure of the airflow over a car by sticking bits of yarn all over it. And it's also possible to get decent numbers, by doing the rolling-down-a-hill-in-neutral test I mention in the Gaspods post. You can even do it with only one test car. And if I were doing it, I'd start with a "normal" car with a CD of 0.3 to 0.35. It would also be instructive to test a vehicle with quite lousy aerodynamics, like a van or pickup truck.

(You can actually even estimate your car's coefficient of drag by rolling in neutral.)

Aerotech vortex generators

These are "Aerotech" vortex generators, sold in sets of 50 for truckers. The rectangular-prism end of a truck trailer is an aerodynamic disaster area, and fuel economy is something of an obsession for many truckers. Anything that reduces drag even a little bit for a long-haul trucker is likely to be worth quite a lot of money; the Aerotech page claims an improvement of "as much as 1%".

For a car, that's not worth paying for, which presumably is why sellers of vortex gadgets for cars tend to be more... optimistic... about their products. One per cent is worth paying for for a trucker, though.

Note that there are also "vortex generators", also known as "turbulence generators", that claim to create a vortex in the air going into the engine, rather than the air flowing over the car. Turbulence generators have been sold in umpteen forms over the years, and have never done a damn thing, except they often do restrict airflow into the engine and thus reduce its maximum power.

This actually often will save some fuel, because now pushing the accelerator all the way to the floor will only give you, say, 80% of what full throttle used to be. Just not pushing the pedal to the floor will do the same thing, though, and still let you have all the horsepower you paid for when you want it.

In light of the panoply of aerodynamic, possibly-actually-effective vortex gadgets on sale, I clearly should have done more research before writing that blog post. As, of course, should the journalists who wrote those happy-clappy articles about the GasPods, never mentioning that they're not actually a new idea.

As that article jaypeabey linked to says (quoting the Bosch Automotive Handbook), you can reasonably expect a given reduction in drag to give you a bit more than half as large a reduction in fuel consumption, at highway cruise speeds. Quite a bit more than half as large a reduction if you're driving really fast, legally or otherwise; no gain worth paying for if you're driving much slower, in traffic.

This is what AutoSpeed found in their dodgy test with the Insight, and, as I said in the GasPods post, there's no strong reason to presume that any of these devices even can somehow give you a larger fuel-economy gain than the drag reduction they deliver.

They're not snake oil, but they do seem to me to be rather oversold.

Cars need more fins

A reader writes:

"Gaspods" - what's your take?

I've got no intention of buying these things, so no money's at stake either way, but I was curious what you thought of this very excited article in Wired today.


I read "gaspods" and I thought, oh, lord, is someone claiming they're the seeds of the gasoline tree?

Wait, no - perhaps they're packaged doses of a magic fuel additive, presented like those coffee-pod things or the little sealed cups of UHT milk.


Actually, thank goodness, GasPods are little stick-on aerodynamic modifier things for cars, designed by one Bob Evans, who seems to have relevant qualifications. Chief among said qualifications is the "Force Fin" swimming flipper, which appears to have been favourably evaluated by the US Navy (I'm not sure why they had to file a Freedom of Information request to get those results, but it'd hardly be the most annoying interaction a business has yet had with a government body...) and also in a university study, although I'm not sure whether that study's ever been published anywhere, which is odd.

But never mind. Dude that made the things has various hydrodynamics qualifications, and hydrodynamics and aerodynamics are similar fields. Good so far.

Commenters on the Wired article weren't very impressed, not least because the article claims Bub Evans has managed to achieve "a 5 percent boost in efficiency for his Volvo Cross Country XC70", which by some wizardry means "a trip that would consume three-quarters of a tank now uses only half". Which would, of course, require a rather more than 5% improvement.

OK, let's presume the journalist misquoted the guy, and Wired's fact-checkers aren't all that they might be.

What claims does the actual GasPods site make, and what evidence do they provide?

On every page, the GasPods site says "Field testers' results exceed the 5% savings predicted by computational aerodynamic performance tests". The About page has a testimonial video claiming a better-than-20% fuel-economy gain in an Audi A4. And the Research page says "Initial Field Studies validate the computational results with participants realizing fuel savings of between 4% and 19%".

Those "computational results" on the research page are the entirety of the actual objective evidence that GasPods do anything at all. Simulated wind-tunnel tests allegedly reduced "the vehicle's drag coefficient by around five percent (5%)," and "Adding GasPods along the rear side of the vehicle further reduced its drag coefficient by an additional 1.6%, to increase the aerodynamic efficiency of the vehicles tested by 6.7%."

But, somehow, GasPods customers are reducing their fuel consumption by up to 19%.

The energy required to push a car through the air increases approximately with the square of the speed, because that's how aerodynamic drag increases. Drag is pretty much irrelevant in stop-start city traffic (unless you're pushing through a really fast headwind...), but the faster you go on the highway, the more drag matters.

Drag is not all that matters for highway fuel consumption, though. The most important other factor is the car's rolling resistance, caused by friction and deformation of the tyres on the road, but in the real world also including the friction and other energy loss in the whole of the rest of the drivetrain. There's also energy used for things other than propulsion, like power steering, electrical systems, the cooling system, air conditioning and so on.

Overall, drag is likely to account for rather more than half of highway-speed fuel consumption, a lot more than half if your vehicle is aerodynamically terrible, and proportionally more and more as you go faster and faster. But it's certainly not the only factor, and reducing drag won't change any of the other factors. (The crazier kinds of automotive talisman are claimed to improve not just drag or engine power, but umpteen other things, up to and including magically cleaning your car.)

The drag of a particular car design, expressed as the "coefficient of drag" or CD, has been a brochure selling point for a long time now. The equation to determine the actual value of the drag for a given car at a given speed is:

FD = 0.5 * p * v2 * CD * A

...where FD is the drag, p is the fluid mass density, v is the velocity, A is the reference area and CD is the coefficient of drag.

So, for instance, if your car has an unremarkable CD of 0.35, and you're driving at 120 kilometres per hour (75 miles per hour, 33 and a third metres per second), through air with a density of 1.2 kilograms per cubic metre, and your car is 1.5 metres high and two metres wide, giving it a "reference area" - sort of its frontal footprint - of three square metres, the drag works out as 0.5 * 1.2 * 33.33^2 * 0.35 * 3, which in this case adds up to the suspiciously round number of 700 newtons of drag force.

For our current purposes, it doesn't actually matter what the drag for a given car is, though. What this equation really tells you is that drag force, all other things being equal, is directly proportional to the coefficient of drag. There's nothing sneaky, like squaring of the CD, going on.

So if you reduce the coefficient of drag by 10%, drag drops by 10%, all other things being equal.

This puts a hard limit on the possible engine-load reduction from a given CD reduction; that limit is equal to that CD reduction, even if drag force is the only thing the car's engine has to work against, and thus the only thing determining fuel consumption.

We know, though, that drag at highway speed may account for more fuel consumption than all other factors put together, but it still doesn't account for all of the fuel consumption. Even if you manage to get a quite large reduction in CD, like 20% for instance (remember, the best computer-simulated reduction the GasPods site mentions is only 6.7%), the best you could reasonably expect that to give you in highway-speed engine-load reduction is about 15%.

A testimonial on the GasPods research page claims a highway-mileage improvement in a 2006 Ford Escape Hybrid from a rated 23 miles per gallon to 29.1mpg, a 26.5% improvement not just in drag, but in actual fuel consumption.

Eeeeeexcept it isn't, because the rated economy is an EPA drive-cycle number (I'm not sure which one; there are several variants of that car), not what you'll actually get in a given long drive. Everybody knows a car will get unusually good fuel economy in a long, flat drive with little accelerating or braking; it's often easy to beat the official "highway" number in a drive like that. For some reason the GasPods page doesn't take pains to point out that 23 miles per gallon was the government-rated fuel economy, not what the car actually got on the exact same drive before installation of the GasPods.

The GasPods people also invite buyers to join the "Test Team" and submit detailed mileage logs, in return for a discount and the warm and pleasant feeling of helping to save the environment.

This is better than the usual magic-car-gadget testimonial standard of "'Ah strapped them magnets on mah fuel line and now mah car sure do go faster!', says Steve No-Last-Name, allegedly of Jackson, Mississippi", but it's still subject to the problems that make uncontrolled, unblinded tests of car-enhancing devices fundamentally useless. Unless you don't know when the magic gadget or potion is being used, with someone swapping it in and out through the test period without your knowledge, and then you average large amounts of driving numbers with and without the gadget or potion, you're not going to get even slightly reliable results from an uncontrolled, non-drive-cycle, test. And blinded testing of a device that's clearly visible on the outside of the car is... difficult.

Without blinded testing, even if you average out large amounts of data rather than just eyeballing the fuel gauge and how fast your car "feels", you're still only going to generate yet another worthless testimonial. People are not calibrated testing mechanisms; you can't become unbiased by just trying to be.

Wait, that's not quite right. Testimonials may be worthless to anyone who wants to know whether the thing being tested actually works, but they can be really useful to people trying to sell that thing. Glowingly positive testimonials are essential advertising material for just about everybody in the woo-woo business, and they're plentifully useful for that, because most consumers don't know how worthless testimonials of this sort are.

Personally, having run into so many big ol' pages of testimonials on Web sites for countless mutually contradictory gadgets, medicines, religions and get-rich-quick schemes, I now take the presence of such testimonials on any site as strong evidence against the validity of the claims being made, even if they've got some real evidence in their favour as well.

I also find it very suspicious that the GasPods people, like the makers of numerous other magical car accessories, seem to be mysteriously allergic to actually doing their own proper tests. Or, heaven forfend, getting a reputable third party to do some tests for them.

For pity's sake, just take two identical cars, put GasPods on one of them, put them both at the top of a hill in neutral and see which one rolls further! (Then run the same test several more times to reduce confounding factors, making sure to test GasPods on both cars in turn, to correct for differences in weight, tyre pressure, bearing condition and so on. You could still get this done in a day, at minimal expense.)

Do these simple tests, use the results to persuade a third party - like a minor university, say - to do better tests without charging you much, use those results to claim the first small share of the billions of dollars per year that a device that really does reduce automotive fuel consumption by a significant fraction is worth, and use that revenue to move on to more and more reputable testers and users. Before you know it, you'll be the first fuel-saving product that the US government actually endorses!

But no. Like every other seller of magical car-enhancement devices and potions, the GasPods people have some skimpy allegedly empirical evidence from tests they did themselves, and plenty of testimonials, and they just sell their wares to anybody who's persuaded by this. (Between $US79.95 and $US124.95 plus shipping for a set of nine Pods! Order today!)

The only rational way to salvage the testimonial claims on the GasPods site is by speculating that reducing engine load by a given amount will reduce fuel consumption by a greater amount - so great an amount, in fact, that it allows an X-per-cent drag reduction to create a greater-than-X-per-cent fuel-consumption reduction, even when you take into account the unchanging rolling resistance and parasitic loads.

Such non-linear relationships do exist, especially at the extreme ends of engine load. When a car's sitting stationary at idle its fuel economy is of course zero, and when it creeps forward in stop-start traffic its miles-per-gallon will be terrible, too. Likewise, heavy load at wide-open-throttle consumes a disproportionately large amount of fuel per distance; a basic fuel-economy tip is to avoid accelerating up hills.

Over small portions of the power range of most engines, though, the relationship between load and fuel economy is pretty close to linear. And this is relevant to the GasPods claims; a drag reduction of 10% or less at highway speeds is obviously not going to make a big difference to engine load, because the engine was far from fully loaded to start with. It might matter to a drag racer, but not to a highway driver. At normal highway speeds you're certainly not going to reduce fuel consumption by almost 20% by reducing your drag coefficient by less than 10%.

So the explanation that reducing drag by a given amount reduces fuel consumption by a larger amount sounds completely demented to me. But it's the only explanation possible for the more impressive GasPods testimonials, besides "these testimonials are rubbish, like almost all other testimonials".

So, do GasPods do something? Quite possibly. The notion that odd changes to the shape of a vehicle can reduce its fuel consumption... not at all implausible.

And, unlike most magic car gadgets and potions, GasPods don't rely for their operation upon the negation of fundamental theories of physics and automotive engineering.

Do GasPods do enough to make them worth the money, though?

Well, the people selling them have no good evidence to suggest this, and the evidence they do offer is very much the same physically-implausible unblinded-test anecdotal testimonial claptrap that's presented in favour of countless ridiculous automotive gadgets and potions.

This is a new product, so maybe they'll have proper evidence to show us soon.

Until that happens, though, I'd keep my money in my pocket.

UPDATE: It would appear that GasPods are not as remarkable, or at least as unusual, as their creators claim. There are actually quite a few vortex-fin products for cars and trucks.

All important physical principles lead to flame-throwers

The inimitable Matthias Wandel, having fun with the Venturi effect.

Great sound, shame about the cancer

A reader writes:

I came across your F5 speaker article...

Kit speakers

...and was very impressed with the information provided.

Is it true that glass fibre batts in speakers can cause mesothelioma? I noticed you linked to the Wikipedia mesothelioma page when discussing polyester and glass fibre batts with the word "carcinogenic".


A ported speaker with glass-fibre wadding inside (it's there to dampen internal resonances) will spit little bits of fibreglass out of its ports in normal use. The cancer risk from these is essentially nil, mainly because the amount of glass emitted is very small. But even larger glass-fibre exposures are generally less dangerous than asbestos exposure, and there's some debate about why this is.

Fibreglass and asbestos are mechanically, and somewhat chemically, similar. Glass-fibre, like window glass, is about three-quarters silicon dioxide (quartz), with the rest being additives, chiefly oxides of light metals, to reduce the glass's melting point and improve its strength and/or chemical properties. All forms of asbestos are essentially silicate minerals too, but with different elements mixed in with the silicon and oxygen.

The most common form of asbestos is the white "serpentine" kind, which is magnesium silicate. Blue and brown "amphibole" asbestos are closer to window-glass, being complicated sodium, magnesium and iron silicate minerals.

Asbestos is so particularly nasty (and useful) because its fibres can be very, very fine, routinely below twenty micrometres (or microns) in diameter, and even down to small fractions of a micrometre, versus around 100 micrometres for a human hair. These ultra-fine fibres are too small to even see, and bits of them can float around in the air waiting to be inhaled. This is why they tent whole buildings and put workers in moon-suits to do asbestos abatement; building materials that contain asbestos can be safe to be near, but as soon as you start busting those materials up, they can produce dangerous and invisible dust.

Fibreglass, also known as glass wool, is made in a similar way to fairy floss ("cotton candy", in the USA); extrusion of the molten material through tiny nozzles. The nozzle size determines the thickness of the filaments, so glass fibres can quite easily be made down to single-digit-micron thickness. As is the case for many other "whisker" materials, most of the desirable physical qualities of the fibres increase as the thickness drops. (This is explored in some detail in J.E. Gordon's classic "The New Science of Strong Materials, or Why You Don't Fall through the Floor", a book that I may not have mentioned on this site for as much as eight or nine minutes.)

Concrete dust and asbestos and glass fibres

This electron micrograph of dust from the wreckage of the World Trade Center (via the USGS) shows a thin glass fibre and a bundle of much thinner asbestos fibres.

(Nobody performed full asbestos abatement on the WTC towers while they were standing, because it would have been very expensive, the asbestos was largely safely bound up in building materials, and nobody expected the buildings to fall down.)

Glass fibres down in the single-digit-micron diameter range are a cancer risk, like asbestos, but glass fibre in general seems to be rather less carcinogenic than asbestos fibres of similar dimensions. Nobody's exactly sure why. Glass fibres don't seem to get stuck in the lungs like asbestos fibres do; this could be purely because of the size difference, or because they don't have the same rough, almost barbed sides...

Asbestos fibres many asbestos fibres (that's another USGS picture).

Glass is also slightly soluble in water, and - it is theorised - fibres in the lungs can thus be slowly eliminated via blood or sputum. For macroscopic objects the water-solubility of glass is essentially zero; you can run water through a glass tube in a laboratory for years with no visible change, and you don't need to worry about rain wearing through your windows. But the thinner the fibres, the greater will be the surface area of those fibres relative to their volume. So even extremely slight solubility can, the theory goes, get rid of the fibres usefully quickly.

It's important to realise that we're not just talking about cancer, here. Most people with asbestos-related lung disease don't have mesothelioma; they've got "asbestosis", a non-cancerous inflammatory disease which can, nonetheless, very effectively destroy your quality of life and in extreme cases kill you. Again, it's the super-fine fibres of asbestos that make it particularly nasty here, but you can get similar syndromes by inhaling various other particulate substances that get stuck in your lungs, like coal dust, and also little bits of fibreglass.

Realistically, even someone who stuffs fibreglass into speaker boxes for a living, without so much as a face mask, isn't at a huge risk of lung disease - cancer, or "just" an asbestosis-like condition. Usually it's people like surfboard manufacturers or insulation installers who get sick, and then only if they don't use a respirator while they're sanding boards or stuffing insulation batts into unventilated roof or floor cavities.

So if you've got ported speakers with fibreglass in them, don't worry about it. Even if you open the speakers up to replace a blown crossover or something, you're in no real danger. (And if you've got un-ported, sealed "infinite baffle" speakers, there is of course even less risk.)

The loudspeaker industry switched to using cellulose acetate or polyester fluff...

Speaker kit parts the normal low-cost anti-resonance speaker-lagging material...

Inside of small speaker enclosures

...some time ago, but I think the change was mainly because these fibres are easier to cut and place, and not a prickly skin irritant, rather than for health reasons.

Incidentally, white asbestos and talc, as in talcum powder and...

Sticks of French chalk and holder

..."French chalk", are chemically the same, both magnesium silicate. Asbestos can metamorphose into talc, though I'm not sure if talc can go the other way. In any case, industrial-grade talc can be expected to contain some asbestos-like filaments.

This fact caused a certain amount of panic among people who've applied talcum powder liberally to their baby, or discovered that standard children's wax crayons contained a small amount of talc, which in turn did or did not contain - depending on who you asked - a tiny amount of actual identifiable asbestos.

(Some people went so far as to allege that because they're chemically the same, talcum powder is asbestos. By this logic, it should be easy to drive nails with a Brillo pad. But have no fear, highly independent thinkers stand ready to help you remove asbestos from your spine with magnets!)

In response to this, more than a decade ago the big-brand crayon formulations were changed to contain no talc. How crayon-talc was supposed to get into kids' lungs in the first place, I'm not sure. Embedding asbestos in wax strikes me as an excellent way of rendering the stuff harmless, even when kids stick crayons up their noses. Perhaps some asbestos could lodge in the digestive tract if they ate it, but I think the normal regeneration of the gut lining would carry it away. Unless you actually lit a crayon fire, I doubt any significant exposure was even theoretically possible.

The asbestos-in-talcum-powder scare was more rational, because people unquestionably do inhale some talcum powder when they use the product in normal everyday ways. There's a difference between bulk industrial talc and the super-fine stuff used for talcum powder, though. Major talcum-powder companies hotly protested that there was no asbestos in their talc at all.

It's rational to take at least some care to prevent you or your baby from inhaling talcum powder, because, as discussed above, inhaling fine insoluble powders in general is a bad idea. But there doesn't seem to be any serious reason to boycott the product entirely.

(There's also a popular belief that laser-printer or photocopier toner is deadly poisonous if inhaled. Actually, toner is just yet another insoluble fine powder. So, once again, you should avoid inhaling it if you can, and wear an appropriate mask if you have chronic exposure to it. But there's no need to panic if you snort a little of the stuff by accident.)

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.

The Ministry of Safer Walks

A reader writes:

I have heard on the worksite (construction; I'm working through college as a part-time fetcher and carrier) that if a power line falls, or someone drives a crane into power lines... should move away from the danger site by taking tiny little steps, or even jumps with your feet together.

But I have also heard that I need to go somewhere and ask for a bucket of compressed air, or a "long weight", or a box of right-handed pipe elbows, on account of we only got left-handed ones here.

Is the pogo away from the power line thing just another way to make people look stupid? Doesn't the electricity get grounded into the... ground?


Oddly enough, this is actually good advice. It may not be necessary in a particular situation, but better to look a bit of a dick and survive than stride away in manly fashion and die.

It's all about the voltage gradient. Connect a power line to ground by cutting it or leaning some metallic object against it and the electricity doesn't just magically vanish at the contact point. If the contact point were an actual earth stake driven deep into the ground then even a quite major power-line short pretty much would disappear right there, but if all you've got is some cable draped on the ground, or big voltages buzzing to earth in scary arcs from this and that part of the frame of a piece of construction equipment, then it's sort of like pouring water onto level ground. Some soaks in at the point where it hits, it spreads out and some more soaks in, it spreads out more and even more soaks in, et cetera.

In this analogy, voltage maps to the depth of water on the surface. The closer to the contact point(s) a given piece of ground is, the higher the electrical potential at that spot will be. This is where the analogy breaks down, though, because you will come to no harm if one of your feet is in two inches of water and the other is in one. If one of your feet is on a piece of ground charged to twenty thousand volts and the other is on a ten-thousand-volt spot, though, you'll have a ten-thousand-volt potential from foot to foot, and you'd better hope your shoes have thick rubber soles with no nails.

Here's an occupational-safety video, as cool and stylish as such videos tend to be, explaining this:

The best thing to do is stay in the vehicle and let the electricity pass around you; the metal frame of a truck is way more conductive than a human, and you're probably sitting on an insulating seat anyway.

If you're in a sparks-and-fire situation best viewed from a considerable distance...

...though, then hopping out of the vehicle so that you don't touch the vehicle and the ground at the same time, and then pogo-hopping away, is the best chance you have to avoid becoming a very crispy critter. (If you don't want to see the severely charred body of a fork-lift operator who lifted his fork into power lines, don't click here.)

Tiny mincing steps can work about as well as pogo-hops, and may be safer in construction-site terrain. The idea is to get away without falling on your face and enjoying the large potential difference that now exists between your knees and your nose.

Even an actual earth stake may become less and less effective as a current sink if a lot of power passes through it for long enough, because that'll heat the area and boil out the water that makes the ground usefully conductive. The same applies to vehicles that are shorting power lines to ground; as the arcing and burning progresses, the area under the vehicle gets drier and less conductive, and the danger zone expands. Usually the power's cut off pretty quickly, but not always.

(For this reason, dry sand and most kinds of desert-dry ground are a bad place to hammer in an earth stake. Since you'll find water just about anywhere if you dig deep enough - this is the Great Secret of Dowsing - you can get around this problem by using a really long earth stake, provided you have some way to pound it into the ground. Hammering in an ordinary earth stake and pouring water around it will work just fine... until the water drains or evaporates.)

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.

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?

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.

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.