Here’s a wonderful tidbit from a book that every physics teacher should have — The Flying Circus of Physics.  My old mentor PD gave it to me with the inscription, “until I write my book of physics stories, this is the best collection of science stories in print.”  As much as I love Paul, I think even he’d have a big task to outdo the wide array of stories and strange facts in this book (though I’d love to see him try!).  Need something to spice up a lecture on sound?  How about an explanation of why we hear our upstairs neighbors more than they hear us?  Or need a story to make the idea of pressure come alive?  How about the girl who got her tongue stuck in a bottle and needed glass cutters to help her get free?

So here’s the story of how electricity helps flowers grow.  We generally think of pollination as being a sort of accidental process — the bee gets himself all covered in yellow snow at one flower, and then loses some of it at the next flower.  No, it turns out that bees get positively charged (they lose some electrons) as they fly through the air.  When the positive bee approaches the neutral flower, that induces a charge in the pollen, which jumps onto the bee.

This is the same phenomenon as when you rub a balloon on your sweater.  The balloon becomes positively charged and when you bring it to the wall, it induces a charge in the wall.  Thus, it sticks to the wall.  There’s a nice simulation of this effect here.

Anyway, the pollen sticks to the hairs on the bee.  If it stuck to the bee itself, it would lose its charge.  The hair acts as an insulator, keeping the pollen grain just far enough away to keep it charged, and thus attracted to the bee.

Now, when the bee goes to the next flower, it induces a negative charge in the stigma of that flower.  The pollen grains are more strongly affected by that concentrated negative charge (the stigma, after all, has more charge than the bee, it’s connected to the ground so has an infinite source of electrons to draw from), and the pollen grain is polarized in the opposite way and jumps to the flower.

Wow.  I wonder if pollination doesn’t work as well in moist climates, then?  Is that why Colorado wildflowers are so stunning in their concentrations?

Bee Picture from TTaylor

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Since I’m woefully behind in posting on my own blog, I’m grateful to Sarah over at a Schooner of Science who wrote up an interesting article on the Chemistry of Kissing.  I was meaning to write something on this topic for a while, actually, since there was an interesting symposium at the AAAS Meeting in February on the Science of Kissing.  They covered several aspects, including the “genetic sampling” theory described by Sarah, below.  Another researcher at that conference did fMRI scans on people who were in love.  You can hear the Science podcast on that interview here. And a detailed report of the AAAS symposium with all sorts of juicy theories about why we like to smack lips here.

Read more of Sarah’s (aka Captain Skellett’s) posts on her main blog at A Schooner of Science.

Here’s her post:

In the words of Henry Finck, “is not a kiss the very autograph of love?” Well, some kisses are better than others Frinck, and it can be hard to tell who’s gonna be good and who’s not. The one who seems perfect on paper can be absolutely shocking in the lips department, while the bad-for-you going-nowhere person can make you weak at the knees after a mere second of lip action. Why the difference?

If you think about it in terms of biological selection, a kiss is a pretty important thing. I consider it a selection factor, cos sure as hell wouldn’t stay with someone who was a crap kisser, and I bet you wouldn’t either. Now, within my friendship group there’s been quite a bit of cross-dating (or whatever the term is) over the years, and I can tell you that the people I think kiss great do not always get the same ruling from my friends. Some couples have chemistry, and some just don’t.

WHY? What are we tasting on their lips? What in a kiss is so important that it is given a make-or-break status in choosing a mate?

The best theory around is that a kiss gives you information (though taste and smell) about the other persons immune system on a genetic level, in particular the MHC complex. Let me tell you the story.

In the dark and murky depths of chromosome six lies a section of some four million nucleotides, genetic material that encode for MHC’s – major histocompatibility complexes. Histocompatibility being a historical term, as it was first identified as determining which blood type you have – A, B, AB or O. The section of DNA on chromosome six encodes for a whole bunch of different MHC molecules, and the alleles are codominantly expressed – meaning you make both the maternal and paternal products.

Behold MHC molecules, there be the peptide binding cleft and there the transmembrane region that acts like an anchor, yarr!

MHC Class 1 molecules are expressed constitutively in all nucleated cells, while Class 2 molecules are expressed only in special antigen-presenting cells of the immune system, like dendritic cell, macrophages and B cells. There’s also Class 3 products that are secreted instead of membrane-bound, but enough blah-blah, on with the story!

Your body can be a bad neighborhood, so police natural killer cells and other members of the immune system drive by frequently to check the ID of your cells, to see if they are terrorists infected or cancerous. If an MHC protein is visible and is only expressing self-proteins, the cell can live another day.

Now let’s say a cell gets infected by a virus, which pokes in some genes of its own so it can hijack our replicative machinery, much like a pirate commandeers a ship to make booty.

Virus oh noes ensue.

Caught red-handed holding non-self proteins, the cell is told to kill itself quietly (apoptosis), or is ruthlessly killed by the immune system in a dramatic action sequence worthy of Schwarzenegger.

Of course, it’s a little more complicated than this. Instead of just two MHC’s on your surface, you have heaps (it took too long to draw!) The MHC region of the genome is extremely polymorphic, and the goal is to have as many different versions of MHC possible, both in your own DNA and across the species. The more variety there is, the more likely someone out there will have what they need to survive HIV or H1N1 or any of the other freaky viruses that get us worried now and then.

So what would happen if your parents ignored the signs given to them by the almighty kiss, and you don’t have much variety in your MHC’s.

The virus slips past the immune system like a ninja, will replicate and spread, and you’ll get sicklier.

So when we kiss someone, we’re really just saying “Hey, how’s your MHC compared to mine? Ooh… you taste different… MAN our kids will have kick-ass immune systems!” Opposites certainly attract in this case.

How did they discover this? They got men to work out, and then asked women to smell their sweaty shirts and pick which one smelled better, and then they ran genetic tests. Women were more likely to dig the stink of a guy whose MHC was very different to her own.

It’s interesting to note that women on the pill are more likely to choose the WRONG PERSON in these tests, possibly because their body thinks it’s pregnant and it’s a bit late to go choosing a mate based on genetics. This could be a contributing factor to divorce – people hook up when the woman is on the pill, they get married, she stops taking it to become pregnant, and suddenly they lose their chemistry. Something to keep in mind.

So go out there and kiss! Sample the MHC molecules around you, and run your own genetic screening! Albert Einstein himself said “any man who can drive safely while kissing a pretty girl is simply not giving the kiss the attention it deserves.”

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Biologist Charlie Carlson over at my favorite alma mater (the Exploratorium museum of science in SF) snapped this photo of me, perky and bright-eyed… but my bench-mates?  Not so much.  Looks like they had a long day of interactive science.

Photo by Charlie Carlson

One thing we found curious about the photo was its graininess in the low light.  Charlie says that it’s because it was highly binned.  I asked him what he meant:

I think that’s the technique used to increase CCD sensitivity.  Individual pixels are lumped together to produce a grainier image at lower lighting.  I may be wrong about that, but that’s what happens with microscope cameras, and under higher illumination the images are much finer grained.

My question was, how does this help the light sensitivity?  There are the same amount of photons hitting your CCD, whether you divide it up into smaller or larger squares.  So obviously it’s not that mechanistic.

Charlie responded:

Maybe gain goes up and the amplified signal just gets down to the noise level of the detector, so random pixels increase in frequency, and the signal has to be averaged over a larger number of detectors to produce the image, and the averaging is what we see.  So that’s my conjecture first thing in the morning.

That sounds plausible to me… but I think I’m waving my mental hands here.  So I looked on Wikipedia (the source of all wisdom) and found out that CCD stands for Charge Coupled Device.  Who knew.   I remember, now, using a CCD for my dissertation.  It was actually fairly accurate, and gave me a count of “1″ for each photon that hit it.  (I was detecting how many photons hit the detector over time, as I shone light on a polymer film.  Long days in the dark.)  Turns out that each pixel on the CCD collects information about the brightness of your object, but the color is spread out over several pixels.  Anyway.  Each time a photon hits the CCD, it knocks free some electrons. The resulting current is what sends a signal that light hit the detector.  The number of electrons created depends on the material. So, I bet that the CCDs in low-end digital cameras don’t create very many electrons, they’re less sensitive.  And thus, one photon hitting a single pixel won’t reliably generate a signal.  So, as Charlie suggests, perhaps many pixels are binned together, so instead you’re generating a signal from 4 pixels gathering 4 photons (instead of 1 pixel gathering 1 photon), for example.  Then the detector just knows that some light hit those 4 pixels, but it doesn’t know where, so you get a grainy image because of this lower resolution.

If anyone knows more, let us know!

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A friend just pointed out an interesting misconception that I hadn’t thought about. When you inhale helium, your voice sounds higher. It turns out that your voice isn’t actually higher-pitched! At least, not in the way that we think it is.  The reasoning is a little convoluted…. read on.

Here’s the common misconception: The speed of sound is faster in helium because it’s lighter than air (thanks to the commenter for correcting me that it’s not the density but the molecular weight of gas that is important here… see Wikipedia on speed of sound). So, they say, since the speed is faster, that means that the frequency of your voice has to increase to compensate if the wavelength remains the same.  [remember, the speed of sound (meters/sec) = frequency (waves/sec) * wavelength (meters/wave)].

Or, another popular misconception is that frequency remains constant, but the wavelength goes up. When this long wavelength hits the air, it then gets converted into a higher frequency. (But if you do the math, you’ll find this logic is flawed, because it actually results in a lower frequency).

Here’s what actually happens, as far as I can figure.

You make sound with your vocal cords… or, more accurately, “vocal flaps” — they look like two fleshy lips slapping against each other rhythmically. See some video of vocal flaps here – look especially at the last one on the right. When you sing middle C, the vocal flaps vibrate together to make a mess of frequencies around middle C, and you change the shape of your mouth and throat to emphasize “middle C” out of the mess of different notes your vocal flaps are making.

In other words, the sound from our vocal flaps doesn’t make it directly to our ears. It resonates in our vocal tract, which picks out certain notes. This is sort of how if you yell into a big tunnel, the echo sounds rather low. That big tunnel “picks out” the low notes. This is why male and female voices sound different — our vocal flaps make the same jumble of notes when we sing or talk, but the vocal tract, or chamber, emphasizes the lower notes for men and the higher notes for women. You can see this if you get a man and a woman and have them sing the same note into a frequency analyzer — you’ll see the same spikes on the analyzer, but the woman will have stronger spikes in the higher frequencies and vice versa for the guy.

So, when your vocal tract is filled with helium, your vocal flaps make that same set of messy frequencies around middle C, but the vocal tract picks it up as a higher frequency. So, in this way, the pitch of your voice doesn’t change (it’s still middle C that you’re singing), but the timbre of your voice does — which frequencies are picked up. Faster speed of sound = higher frequency. (The wavelength is fixed by the size and shape of your mouth and throat).  So, it’s true that what you’re hearing is a higher frequency, but the difference is in what happens to air in the chamber of your mouth, after you’ve produced the sound.

Here’s what the March 1987 edition of Scientific American says in an article titled “Sopranos of the Skies”:

When a soprano sings a high C, her vocal cords actually produce a broad band of frequencies. . . . If [she] inhales helium, her voice seems to rise in pitch not because her vocal cords vibrate faster in the less dense atmosphere (they do, but only slightly); rather, because sound travels almost twice as fast through helium as it does through nitrogen, the acoustic properties of the vocal tract change so that it resonates with and amplifies higher-frequency tones.

For those of you who like math: When your lungs are filled with air, and you sing middle C, it has a frequency of 261 hertz and the speed of sound in air is 333 m/s (that’s 770 mph!), with a wavelength of about 1.27 meters (or about 4 feet, neato). When you inhale helium, the speed of sound is faster (972 meters/sec) because helium is lighter than air. Well, if the frequency created by your vocal flaps is the same, and the speed of sound goes up, then the wavelength must also go up. Using speed = frequency * wavelength again, you can calculate that the wavelength of the “middle C” that you try to sing on helium is actually about 3.7 meters long.

But here’s the real puzzler!  What happens when the sound leaves your helium-filled mouth and hits your ears? Why doesn’t that long wavelength just get downshifted to a shorter wavelength when it leaves your mouth and hits the air (so that you hear the regular “middle C” that the soprano was trying to make)? It’s because frequency has to stay the same, or “frequency is conserved”. If 300 pushes of air leave your mouth every second, then 300 pushes of air have to travel through the air outside your mouth as well or else you’ll get a traffic jam of air leaving your mouth (this is the same argument, roughly, as to why water has to leave a pipe at the same volume per second as it enters the pipe). Below is from the New Scientist:

Once sound leaves the mouth its frequency is fixed, so the sound arrives to you at the same pitch as it left the speaker. Imagine a roller coaster ride. The car speeds up and slows down as it goes around the track, but all cars follow exactly the same pattern. If one sets out every 30 seconds, they will reach the end at the same rate, whatever happens in between.

In stringed instruments, the pitch depends on the length, thickness and tension of the string, so the instrument is unaffected by the composition of the air. Releasing helium in the middle of an orchestra would therefore create havoc. The wind and brass would rise in pitch, while the pitch of the strings and percussion would remain more or less the same

You can see some other writings on this at the Straight Dope and the New Scientist.

Note that you can have all sorts of crazy fun by breathing in sulfur hexafluoride. Well, actually, don’t do it, but instead watch it in the below YouTube video.Sulfur hexafluoride is heavier than air, so it has the opposite effect. A balloon filled with sulfur hexafluoride feels heavy, like it’s filled with water or foam. And that’s why you shouldn’t do this at home — since it’s heavier than air, it sits in your lungs and you can’t expell it. You have to turn yourself upside down or over a chair for a few moments to get it out of your lungs.

I’ve inhaled sulfur hexafluoride and I have to say, it was one of the strangest sensations! It felt like I was trying to talk through mud.

Here’s another video that shows a neat demo about how heavy sulfur hexafluoride is.  At the end they “float” a little aluminum boat on a “sea” of sulfur hexafluoride (which sits, invisibly, in a container. It’s a gas but doesn’t float away because it’s heavier than air). They then scoop some of the gas into the aluminum boat and you can see it slowly sink as it’s filled with the invisible gas….

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A recent volume of Science News had a feature article about attraction and the evolutionary basis of our conception of what makes someone beautiful.  As writer Elizabeth Quill says (I love this quote) — “For humans, there is osmething captivating and unforgettable about the arrangement of two balls, a point and a horizontal slide on the front of the head.”  Put that way, it’s pretty darn surprising, isn’t it?  Turns out that our brain gets the same dose of dopamine rewards from seeing a pretty face as from food, drugs or money.  Would we press little levers to see pictures of Brad Pitt like a rat presses a button to get doses of cocaine?  Food for thought.

Anyway.  One of the major points of the article was that we find composite faces — those that are very average, with irregular features smoothed out — very attractive.  They figured this out back in the late 19th century when Sir Francis Galton made composite photos of criminals to try to get a prototypical “criminal” face.  He found the result to be surprisingly, well, beautiful.

You can make your own average faces at faceresearch.org. You can also make a baby by uploading the mother’s and father’s faces!

Here’s one I made using just women’s faces:

faceresearch.org

And here’s one I made using just men’s faces:

faceresearch.org

And here’s one using a mix of men and women.  Trust me, the faces I chose were pretty non-beautiful overall.

copyright faceresearch.org

Also some surprisingly beautiful faces at Anthony Little’s website, alittlelab.com. I’m struck by how much I like looking at these average faces.  I definitely feel those dopaminergic receptors having a little party.

Symmetry was also mentioned as an aspect of attractiveness (a symmetrical face is more attractive), which can be a sign of health.  I’ve heard the “symmetrical faces are attractive” argument before — this article suggests that symmetry may not be as important as indicated previously. Here’s a face made symmetrical and antisymmetrical.

Also, whether a face is more masculine or more feminine can affect its attractiveness, and women are especially affected by these factors when they’re ovulating!

Read the original Science News article and see some more interesting pictures of morphed faces.

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In this week’s episode of Science Teaching Tips, we look at my favorite thing — light.  Light, like, rulez.  Dude.  And so does my old mentor, Paul Doherty, who will tell you one of his best stories from the history of science about how the spectrum came to be the spectrum.  I mean, what the heck is indigo anyway?  The answer turns out to be, like all good history of science stories, steeped in mysticism and superstition.   Give it a listen, it’s a good story!

Episode 65:  Revising the Rainbow.

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I got a lot of comments on my previous post on synthesia, so it seems there’s some interest there.  Check out this post on Cognitive Daily about a study of the rarest form of synthesia – tasting words.

For more common (or rather, less uncommon) forms of synesthesia, the most convincing evidence that it’s real comes from studies showing that synesthetic associations are stable. If “A” is associated with the color blue now, it will still be associated with blue six months from now. What’s more, sometimes the letter-color associations are the same for different people. With only one example to study, this type of evidence is harder to come by, but at least Gendel could test TD at different times and see if her associations were stable.

Gendel presented TD with 806 randomly selected words, and 222 nonsense words created from English-language sounds. She was asked to write down what taste (if any) she associated with each word, and rate the strength of the association. Then the test was repeated three months later. Almost 50 percent of the time, TD experienced a taste sensation accompanying the word. In those cases, 88 percent of the time that sensation was identical or nearly identical three months later. Stronger taste sensations were significantly more likely to be repeated at the end of the study.

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Why is it that your fingers get all wrinkly when you’re in the bath too long?

It’s a pretty simple little answer.  You know how a spongue gets bigger when it gets wet.  The outer layer of our skin is like that too — it soaks up a bunch of water and gets swollen.  But it can’t just get big and puffy because it’s firmly fastened to the layer of skin underneath.  But that extra surface area has to go somewhere, so it buckles up into folds, and wrinkles.  This happens after a long time in the bath because the skin oils (sebum), which usually protect your skin, eventually washes away, letting the water in to your skin.

As a commenter on the Wonderquest site put it,

My high school biology teacher explained it as: you have a size 3 finger and size 3 skin. After you have been in water, you still have a size 3 finger but now you have size 7 skin.

This is all in the epidermis, the outermost layer of our skin.  The stratum corneum is the part that is on the outside, and it’s got a bunch of dead keratin cells.  Keratin’s the stuff found in our hair and fingernails.  The dead keratin cells absorb water.  It happens mostly on our hands and feet because those parts of our body go through a lot of wear and tear, so they’ve got more dead keratin cells on them than, say, the sensitive and soft underside of our arm.

Great physiology and physics!

More on the Library of Congress Everyday Mysteries Site, and Wonderquest.

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Here are some fantastic photos from the New Scientist website — accidentally captured the clearest picture of a woman’s ovary in the process of ovulation.

Pictures and articles here

I guess it’s pretty hard to get pictures of an event that happens for just a few minutes at one poorly determined time each month. They just happened to have this woman already cut open at the time (she was getting a partial hysterectomy). What luck. Apparently the main scientific result of the images is that the process happened much slower than previously thought — it took about 15 minutes for the egg to emerge.

I was actually just as interested to see the ovary and the follicle themselves (the follicle is *huge*!) as the emergence of the egg.

Hmm, a funny post for Father’s Day, I realize!

And, congratulations to me, I turn 100 today!  This is my 100th post…

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Yesterday’s post in Engineering Life talks about the questions that are raised by genetic engineering, and whether we ought to be more worried than we are. I wanted to take the chance to point you to WNYC Radio Lab’s (So-called) Life episode, which talks about just this — what is life, what counts as natural? Brilliant radio. Listen to it!

Engineering Life’s blogger Carl Zimmer writes:

Imagine that mad scientists defied nature and violated the barriers between species. They injected human DNA into non-human creatures, altering their genomes into chimeras–unnatural fusions of man and beast. The goal of the scientists was to enslave these creatures, to exploit their cellular machinery for human gain. The creatures began to produce human proteins, so many of them that they become sick, in some cases even dying. The scientists harvest the proteins, and then, breaching the sacred barrier between species yet again, people injected the unnatural molecules into their own bodies.

This may sound like a futuristic nightmare, the kind that we will only experience if we neglect our moral compass and let science go berserk. But it is actually happening right now. Today millions of people with diabetes will inject themselves with insulin that was produced by E. coli.

The fact that no one is disturbed by this state of affairs says a lot.

But thirty years ago, the public rebelled against the same idea — of sticking genes into E. Coli so that it would produce human insulin. The project was condemned by many activitists. And yet…

We suffered no epidemic of diabetic comas, no cancer viruses spread by E. coli from host to host. None of the dire warnings about engineered E. coli, in fact, came to pass. It appears that the safeguards put in place were good enough, and that engineered E. coli could not compete with its wild cousins. Scientists continued to engineer E. coli, and today it can make all manner of substances, from blood-thinners to jet fuel

Today we’re capable of much more than this with genetic engineering, including the engineering of chimeras (beings created by mixing cells that originated from two different beings).

It’s not quite clear to me where the Engineering Life blogger (Carl Zimmer) stands on the issue, as he finishes with a less cautionary, more relativistic stance:

But it’s also important to bear in mind how easy it is to be terrified by a science-fiction caricature of what’s really going on in synthetic biology labs. We have a profound distrust of what seems unnatural, such as crossing species boundaries. Yet a casual glance at E. coli’s genome demonstrates that nature has been inserting foreign genes into it by the hundreds for millions of years. Our own genome is not immune from these violations. We carry the remains of thousands of viruses in our DNA, and most people on Earth may even carry genes inherited from another species of human–Neanderthals. We may be disgusted by the thought of violating species boundaries because of deeply ingrained instincts. But that disgust is an unreliable guide to the realities of biology, whether that biology is in E. coli or in ourselves.

I’m not really sure where I stand on the issue, to be honest. I don’t have an emotional reaction to mixing species — the “disgust” response outlined above. But I am cautious about introducing new creatures to our world, as the law of unintended consequences often seems to hold. But I feel somewhat powerless to make a stand one way or the other. I was not in favor of putting GMO corn out in the cornfields, and now look where we are — GMO corn has spread all over North America on the wind. Did we used to have more control over these new innovations, or has the public always felt unable to enter the debate about what is done in their world?

[Crossposted on Engineering Life]

[Picture: "The Young Family," by Patrician Piccini (2002-3). Wikipedia]

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