Category Archives: science/maths


Here’s what happens to an ant’s abdomen when it eats green sugar solution:

close-up photo: ant with translucent green abdomen eating green sugar solution

 It’s one of a set of photos I came across today. The others are well worth seeing and are in this Mail Online article. (Lest you judge me, I should point out that I arrived on the photos via my Tweeted Times page, not via anything to do with the Daily Mail.)

There’s nothing  particularly special about the ants: according to the article they’re just ones that were in the back garden of the photographer, Dr Mohamed Babu, whose wife noticed that one that had been drinking milk had a white abdomen.

The article is quite  interesting (and all three photos stunning), though I did find it amusing that rather than just calling him by his name the Mail felt obliged to call Dr Babu “father of three Mohamed Babu” and “the 53-year-old”. They also call him “Scientist Dr Babu”, but infuriatingly they don’t say what kind of scientist. Particle physicist? Cosmologist? Seismologist? Entomologist? Ants are less central to some of those disciplines than to others . . .

And presumably his age and number of children have some bearing on ant photography or they wouldn’t have mentioned them, but I still haven’t quite cracked that one.


While I’m at it—here’s something else which initially looks impossible until you work out the basic principles behind it. Which I’m sure you can. 😉 Having written about the levitating Slinky earlier, I’m not going to write another 1300 words now explaining that the radius can vary how you like provided the combined radius of the two gears is always equal to the how it works.

Just some wooden gears. The wheel, reinvented.

Impossible Slinky

What happens when you drop a Slinky? Specifically, what happens if you let it dangle down motionless, then let go of the top end? It falls, right? And maybe bounces around a bit as it does so?

Here’s a slow-motion video. I came across it the other week. Unless you’ve either seen it before or carefully worked out the physics, I think you’ll be quite startled.

It looks utterly impossible. Most of the Slinky apparently levitates, remaining almost completely stationary for most of the time, while the top part falls. YouTube being YouTube, last time I looked some of the comments were from people refusing point-blank to believe the explanation in the video. I’m not sure what they wanted the explanation to be—maybe some kind of impossible magic more in keeping with the impossible-looking behaviour? I don’t know.

The video talks in terms of information about what’s happened at the top of the Slinky taking time to get to the bottom. Although that’s accurate, I found a different way of looking at it more helpful. I need to explain a bit of very basic mechanics, though. Just one of Newton’s Laws of Motion.

Before Newton, a popular idea was that in order for something to move, you had to apply a force to it. Give it a push or a pull. This seems reasonable from everyday experience: something resting on the table will stay there until some force makes it move, and to drag a heavy object across the floor you have to keep on pulling all the time it’s moving.

That’s not actually the case, though. Everyday heavy objects need a force to keep them moving because there’s another force, friction, resisting the movement. What forces do is to accelerate objects: that is, to change their velocity. Start something moving in empty space and it’ll just keep on moving in a straight line unless you apply some force to change the motion. How much force? Newton’s Second Law answers that: force equals mass times acceleration. That is, to accelerate something weighing 2 kg by as much as something weighing 1 kg, you need to push twice as hard.

“Yes but what about gravity?” I hear you saying (whether you are or not). “That’s there all the time, and I can feel it pulling me down into my chair, but I’m not accelerating at all. I’m just sitting here. I’m not moving and I’m not starting to move either. And all the things on the table are just sitting there too.”

The answer, of course, is that there are two forces acting on you: gravity pulling you down, and the chair pushing you up. They cancel out so you don’t accelerate.

“Yes but why do they cancel out? Why is the force from the chair just the right size?” That bothered me when I first learnt basic mechanics. One answer is simply to cite Newton’s Third Law: “To every action there is an equal and opposite reaction”. The chair obeys this and reacts to gravity pulling you down onto it by pushing up against you. The Third Law says the forces are equal and so they are. But that doesn’t seem much like an answer. It amounts to “The forces balance simply because they do, and we’ve got a name for it: Newton’s Third Law of Motion.”

OK then: what would happen if the chair didn’t push quite hard enough? It wouldn’t quite cancel out the gravitational force on you, so you’d accelerate downwards. Into the chair. Squashing the upholstery and thereby making it push a bit harder, so you accelerated less . . . you’d overshoot a bit and bounce up again . . . and after a few bounces you’d end up stationary, at exactly the right point for the two forces to cancel out. The forces have to be equal because if they weren’t, they’d adjust your position until they were.

If you put a mug of tea on the table, the same explanation applies, but on a smaller scale. The outer electrons of the atoms of the two objects are repelling each other. Push them closer together and they repel more. Instead of macroscopic bouncy upholstery we’ve got a microscopic bouncy electric field. The mug rests in just the right place for  the repulsion to cancel out the gravity trying to pull it through the table.

The key thing is: stationary objects around us stay stationary because the net force acting on them is zero. They accelerate when the forces are out of balance.

How does all this relate to the Slinky? And why, when you let go of the top, doesn’t the force holding it up disappear so gravity wins and it accelerates downwards? Why does it “levitate” so counterintuitively? Surely it’s disobeying everything I just described?

Consider just one small piece of the Slinky. Imagine holding it in your hand, gently pulling one turn of it away from the next. To stretch it further, you have to pull a little harder. A given amount of stretch requires a precise strength of pull; a given strength of pull produces a precise amount of stretch.

Now consider the dangling, stationary Slinky. Think about just one turn of the spring. It has three forces acting on it:

  • The turn above is pulling upwards on it. How hard depends solely on how far apart the two turns are.
  • The turn below is pulling downwards on it. Again, how hard depends just on how far apart the two turns are.  (They’ll have stretched just enough to support the part dangling below.)
  • Its own weight is also pulling downwards.

Before the Slinky is dropped, the three forces are in balance, so the turn we’re looking at remains stationary. It has to; moving would require accelerating. That would require at least one of the forces to change, so they didn’t balance any more. They won’t change unless one of these changes:

  • The weight of this turn of the Slinky—which is constant.
  • The distance between this turn and the one above. This requires the turn above to move (this one won’t until the forces change).
  • The distance between this turn and the one below–i.e. the turn below must move.

In other words, the only way for a turn within the Slinky to start moving is for an adjacent one to move first.

The top turn is supported not by another turn above, but by an upward force from your fingers. When you let go of the Slinky, you simply remove this force. Now the only forces acting on the top turn are its own weight and the pull of the turn below. So it accelerates downwards, becoming the first one to move. This moves it closer to the turn below. The reduced stretch means the two turns don’t pull on each other quite so hard, so the one below no longer has quite enough upwards pull on it to keep it stationary, and it too starts accelerating.

But further down the Slinky, where nothing has moved yet, the turns are spaced  just as before. Since the pull between them depends only on their spacing, it is unchanged. Neither has the pull of gravity changed. So the forces remain in exactly the same balance, happily continuing to cancel each other out. There’s nothing to start those turns moving; they have to remain stationary.

You know from playing with such things that if you waggle one end of a Slinky or similar, a wave of movement travels along it. The same happens here: it takes time for the pulling together of adjacent turns to travel down the Slinky. And since none of the turns can start falling until the wave reaches them, they remain suspended in that impossible-looking way.

Yes but—it still seems wrong. What’s holding the bottom part up now you’ve let go? How can it hang there with nothing to hang from?!

Imagine doing pull-ups: you pull yourself up towards the bar by pulling down on it. Similarly, as the bottom part of the Slinky hangs down from the top part, it supports itself by pulling down on the top part. Once you let go, it continues doing exactly the same thing. It’s still hanging from it. The only difference is that the downward which previously went into resisting the upward pull from your hand now goes into making the top section fall faster than it would under gravity alone. It’s being forcibly accelerated downwards,  and the reaction to that accelerating force is what supports the stationary section.

The Slinky is simply behaving the way it has to.

And yet, it still looks impossible. And it took more words to explain than I expected.

Boatswains and silicon

What do particle physics and breast implants have in common?

BBC mispronunciation, that’s what! I’m not sure whether this is a worrying trend or just a worrying longstanding tradition, but lately I’ve noticed what at least seems like an increased carelessness on the radio about the pronunciation of slightly difficult words. In some cases this is merely a bit irritating—as with the routine pronunciation of Angela Merkel as Anjullah Murkle, which probably just means the speaker is unfamiliar with how to say German words—but in other cases it’s downright misleading. Two of the latter variety have been in the news a lot over the last few days; meaning that the misinformation has been reinforced over and over again in various news bulletins.

Interestingly they both involve the same syllable, -on, in entirely different contexts. In one case it’s mispronounced; in the other it’s said instead of the correct syllable. Specifically:

Bosons are not boatswains

If newsreaders on Radio 4 are to be believed, physicists (sorry, generic scientists) working at the Large Hadron Collider are close to confirming the existence of something called “the Higgs Bosun”. Bosun is one of those words whose spelling used to be littered with apostrophes representing omitted letters. It is now spelt either bo’sun, bosun or boatswain. (Boatswain is the original form, and the other two are derived from it, presumably because its pronunciation is so different from its spelling.) The vowels rhyme with those in open.

I’ve never been quite sure what a boatswain was, other than that it was some role on a boat. So I looked it up. According to the OED:

boatswain (also bo’sun or bosun) n. a ship’s officer in charge of equipment and the crew.

So they run the LHC like a ship and they’ve spent all this time wondering whether the the bosun exists or not, but now they’ve finally half-glimpsed him? He must spend a lot of time working from home, then . . . Or is the Higgs a ship and he’s in charge of its equipment? Ah, that must be it. He’s not the Higgs Bosun but the Higgs’ Bosun. Bosun of the Higgs. Arrrrrr.

But of course what they really mean is the Higgs Boson. The OED defines a boson as

boson n. Physics a subatomic particle, such as a photon, which has zero or integral spin.

Ah, that’s it. The entry also includes a reminder that such particles are named after the  Indian physicist S N Bose.

The s  of boson is pronounced like a z, and unsurprisingly the word rhymes with ones such as photon, proton and Vogon. The -on is pronounced like the word on.

Its mispronunciaton as bosun puzzles me. Surely even newsreaders have heard of electrons, protons, neutrons, photons . . . ? OK so they may not have heard of fermions, leptons, nucleons, mesons, kaons, pions, gluons, gravitons, positrons or (a favourite from when I studied electronics) phonons, but the basic principle is clear enough: huge numbers of particles have names ending in -on, and in every case it’s pronounced the same way. Why would it suddenly change just because of a superficial resemblance to the term for a ship’s officer?

Silicone is not silicon

The other piece of news lately has been about women’s breasts. Specifically, ones containing what the newsreaders and even some of their expert interviewees have been calling “silicon implants”. There have been concerns that some of these may have been made using “inferior quality silicon”.

Rather than go to the OED, I’ll give you my own definition of silicon, focusing on its most relevant features. I had rather a lot to do with silicon when I was studying electronic engineering. It is

silicon n. A very hard, brittle, rigid, reflective material whose appearance is between that of glass and a metal such as steel. It has a crystal structure similar to that of diamond and is used in electronics for its semiconductor properties. Silicon is the chemical element Si, occurring naturally in the mineral quartz (silicon dioxide).

Probably your best bet if you want to see a piece of silicon is to have a look at a solar panel, which is likely to be made out of it. A piece of silicon crystal basically looks like a piece of metal made out of glass, insofar as that’s a possible appearance for anything to have.

Whenever I hear the phrase silicon implants I immediately expect to hear something about electronic devices (“silicon chips”, “microchips”) being embedded in people’s bodies—maybe for purposes like allowing nerve impulses to control prosthetic limbs, or to let artificial retinas send signals to the optic nerve to help blind people see.

You seriously don’t want to be making breasts out of silicon.  Or at least not if you want them to be anything like real ones. If your thing is razor-sharp nipples which cut through anything they touch, or built-in body armour, then maybe. But stainless steel would be cheaper.

What they mean, of course, is silicone. This doesn’t just refer to one material, but to a whole range of them including oils, substitute rubber, and squishy plastics. There’s a Wikipedia article about silicones here. The -one is pronounced exactly the same way as it is in traffic cone, telephone, semitone and the like.

The key difference between silicones and ordinary plastics is that whereas those are based on long chains of carbon atoms, silicones instead use long chains of silicon atoms alternating with oxygen atoms. So the best way to think of them is as plastics, oils, greases etc based on silicon instead of carbon.

But emphatically don’t think of silicones as silicon: calling the material breast implants are made from “silicon” is as ridiculous as calling alcohol or rubber “diamond”. Even if you’re the Higgs‘ Boatswain. And definitely if you’re a BBC newsreader.

A music-and-science blog

The two things I find the most immensely interesting and continually impressing are music and neuroscience . . . Philosophy and politics are my second loves.

Science and music often go together—many of the best amateur musicians who I know are GPs, for example—but they aren’t all that often explicitly put together in blog form.

Today I finally got round to having a look at Science with Moxie, which is Princess Ojiaku‘s blog on the Scientific American Blog Network. If you’re interested in both science and music you should probably have a look. And if you’re interested in the science (not solely neuro-) of music you should definitely have a look.

The most recent post, for example,  describes brain-imaging experiments designed to look at the brain’s processing of words, pitch and rhythm. All three elements are present in both singing and speech, so (for example) is there a difference between the brain’s processing of pitch in speech and its processing of musical pitch? It also includes a nice video illustrating the way in which a fragment of speech, when repeated, begins to sound like a fragment of song in which the individual notes are so well defined that a listener can sing the tune back.

I’m tempted to list more of the posts but really, the best way for you to find out what’s there is to go and see for yourself . . . which I hope you will.