Wikipedia:Reference desk/Archives/Science/2008 August 29

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August 29

Motorcycle

I have seen motorcycles turn, not by turning their steering wheel, but by leaning their bikes towards the ground. Why does this work. I've draw a free-body diagram, but I can't find the centripetal force. —Preceding unsigned comment added by 65.92.231.82 (talk) 00:27, 29 August 2008 (UTC)

Bicycle and motorcycle dynamics has everything you could possibly want to know. Algebraist 00:31, 29 August 2008 (UTC)

I think it's because motorcycles are fast enough that you need to lean significantly even with a wide turning radius. In short, the amount you lean the bike is noticeable, but the amount you turn the front wheel isn't. In addition, do the the way bikes are built, leaning causes the front wheel to turn. — DanielLC 00:52, 29 August 2008 (UTC)

In response to DanielLC, I'm sure it's a centripetal force causing the acceleration, and I'm also sure it's firction. I checked the article Bicycle and motorcycle dynamics, specifically turning, but they didn't why the friction force appears, or the derivation of the formula. —Preceding unsigned comment added by 65.92.231.82 (talk) 01:24, 29 August 2008 (UTC)

Friction provides centripetal force on a flat corner. On a banked corner, centripetal force is a combination of horizontal components of friction and normal force. Gandalf61 (talk) 10:22, 29 August 2008 (UTC)

Also note... They are turning the wheel, slightly in the opposite direction that they are turning. Let me see if have an article on it... counter steering. Wow! -- kainaw™ 14:12, 29 August 2008 (UTC)

Well, that article on counter steering was great. I never understood the physics. Now I know. OrangeMarlin ^{Talk• Contributions} 00:51, 30 August 2008 (UTC)

Clorox as hair lightener/bleach

Regardless of safety, can clorox (or similar) bleach effectively lighten hair? As an oxidizer, I would think that it would be mightily effective. Please also describe potential side effects of this procedure. Thank you. Kenjibeast (talk) 01:05, 29 August 2008 (UTC)

(from accidental experience) Yes, it will alter the color of hair. No, it will not make it blond. Yes, it will turn it a weird copper-green color. No, it will not look healthy. Yes, it will become thin and stiff and break when you try to brush it. No, it will not feel good. Yes, it will burn and leave a permanent thinning-hair spot on the back of your head that is still visible after 20 years. -- kainaw™ 01:35, 29 August 2008 (UTC)

Concur from the memory of the appearance of a friend's hair and the state of his scalp after he tried to bleach his hair using toilet bleach. It started falling out in clumps the day after - and the sores, they did weep. Not the best idea. --Kurt Shaped Box (talk) 19:27, 29 August 2008 (UTC)

Perception of Musical Pitch

Is there any evidence that peoples perception of musical pitch deteriorates with age?--79.76.200.98 (talk) 02:07, 29 August 2008 (UTC)

It's mentioned in Cecil Adam's column on Perfect Pitch but it's not referenced. APL (talk) 02:59, 29 August 2008 (UTC)

Under Limits of Perception, http://en.wikipedia.org/wiki/Psychoacoustics it says, "The human ear can nominally hear sounds in the range 20 Hz to 20,000 Hz (20 kHz). This upper limit tends to decrease with age, most adults being unable to hear above 16 kHz." In fact, hearing ability in the entire upper audio range typically tends to decrease as a person ages. I cannot find an authoritative source for that statement, but I am sure there are authoritative sources. Andme2 (talk) 04:32, 29 August 2008 (UTC)

I don't think that was exactly the question. Yes, the upper audible limit deteriorates markedly with age but the questioner is instead asking is the human ability to reproduce an exact frequency age related. For instance, when an orchestra is tuning up before the start of a concert, the lead violin will play a note A 440Hz for the rest of the violins to reference to. There are no frets on a violin - the note is placed at the correct frequency entirely by ear. It is essential that the lead violin has perfect pitch to accurately reproduce the required note. 440Hz is a relatively low frequency, well below the normal age related deterioration. If the player has lost the ability to hear this frequency then he/she has substantially gone deaf. I don't know the answer to the original question but my guess is that perfect pitch is not related to the physiology of the ear and that deterioration in the function of the ear (provided it has not gone too far) does not affect this ability. I think that this rather wonderful skill is more likely an ability of the brain. SpinningSpark 06:16, 29 August 2008 (UTC)

It's almost always the oboe that sets the orchestra's pitch, and not a violin, precisely because the oboe's pitch is more or less unalterable by the player once it's established, while the same is not true, as you point out, for the strings. - Nunh-huh 06:59, 29 August 2008 (UTC)

Also, because of tuning forks and electronic tuners, no one in an orchestra needs perfect pitch. It's a cool ability, but many (I expect most) professional musicians don't have it. --Allen (talk) 19:48, 29 August 2008 (UTC)

The Mosquito, as well as the ringtone derived from it, were based on this assumption. As for references, I found this webpage from Hypertextbook.com, which claims:

"The range of hearing for a healthy young person is 20 to 20,000 hertz. The hearing range of humans gets worse with age. People lose the ability to hear sounds of high frequency as they get older. The highest frequency that a normal middle-aged adult can hear is only 12-14 kilohertz."

and

"The normal range of hearing for a healthy young person is 20 to 20,000 Hz; hearing deteriorates with age [...]"

I once used Frequency Generator to test whether the maximum frequency decreases with age, and found the correlation was startlingly strong; a sound that one person considered unbearably loud was inaudible to a person only several years older. --Bowlhover (talk) 06:29, 29 August 2008 (UTC)

I don't have a source at hand at the moment, but I think that statistically speaking, on average the upper limit of hearing decreasing with age. As for whether the ability to perceive pitch changes at any frequency, including the mid-range, decreasing with age, I haven't seen anything to suggest that. It could be, but there are plenty of elderly musicians who play instruments such as the violin that require sensitive pitch perception. In any case it would have something to do with the inner ear's hair cells. It wouldn't surprise me if over time there is some kind of loss there. Pfly (talk) 07:22, 30 August 2008 (UTC)

I remember reading somewhere that Benjamin Britten had complained of standard pitch seeming to grow sharper as he aged. Google throws up an article about an NPR program which bears that out: "Our results clearly show that as people get older, they are perceiving things sharper than when they are younger," William Avery (talk) 15:07, 30 August 2008 (UTC)

I don't know how this relates to perceived musical sharpness, but the perceived sound of musical instruments becomes somewhat different as a person ages. All musical instruments produce complex (non-sine wave) tones. The sensitivity to higher pitches typically decreases as a person ages. Therefore an older person hears a less complex tone, somewhat closer to a sine wave. This would occur even at low fundamental frequencies. Also, of course, the perceived loudness of pitches with a high fundamental frequency decreases - that is a second effect. Andme2 (talk) 06:34, 31 August 2008 (UTC)

Transverse waves

Why can't transverse waves pass in liquids? I can see why they can't pass in gasses, but why not in liquids? —Preceding unsigned comment added by 65.92.231.82 (talk) 02:11, 29 August 2008 (UTC)

Clearly they propagate nicely along the interface between water and the air above it. It seems that to propagate within a body of liquid, there would have to be an interface within the liquid, such as a layer of fresh water above a layer of salt water where a river flows into the ocean, or the interface between oil and water. Longitudinal waves propagate nicely within a homogeneous liquid. Edison2 (talk) 04:46, 29 August 2008 (UTC)

The liquid has no strength or stiffness. It does not resist movement like a solid, so there is no restoring force to make a wave. However the liquid does resist compression, so you can get a compression wave. Graeme Bartlett (talk) 05:55, 29 August 2008 (UTC)

Why would it work in gasses but not liquids? The only difference is that gasses compress when under pressure. — DanielLC 17:22, 30 August 2008 (UTC)

Why is mescaline a controlled substance?

What are the detrimental effects of it, if any? False Tournament (talk) 02:41, 29 August 2008 (UTC)

Why is it controlled? See Convention on Psychotropic Substances. -- kainaw™ 02:47, 29 August 2008 (UTC)

I heard of on- and off-pills used by the military so the pilots are guaranteed awake for combat and have a sound sleep afterwards. Can't find any reference on the net right now, though. Does anybody know about that and why it's allowed? If it is allowed, can I have access even if I'm not at war with anybody? 93.132.129.229 (talk) 19:53, 29 August 2008 (UTC)

The USAF (and probably other air forces) prescribe amphetamines to some of their pilots (e.g. B2 and B52 operations to Iraq based in the US and the UK respectively) where the pilots had to stay awake for long periods of time (reference). They do this under the control of a flight surgeon (a doctor), who is supposed to make sure their use is appropriate and the side effects managed. You may wish to consider whether you're comfortable with someone taking a drug which has side effects including nervousness, irritability, over stimulation, restlessness, euphoria, and feelings of suspicion and paranoia (reference) is a fit person to be in charge of weapons and aircraft. Lots of things are legal for the military to have (machine guns, tanks, nuclear armed submarines) which are nevertheless illegal for ordinary people. -- Finlay McWalter | Talk 20:03, 29 August 2008 (UTC)

I see, so this is because they have machine guns, tanks, nuclear armed submarines and so on, so no one can effectively deny those rights to them. 93.132.129.229 (talk) 20:32, 29 August 2008 (UTC)

No! That's completely untrue - and I'm very sure you know that. They have the right to use these drugs AND they have the right to use tanks, etc because the law/constitution of the country (rightly or wrongly) permits it. Your take on it would suggest that they demand the drugs and get them because they're heavily armed...that's a totally ridiculous point of view. Correlation does not imply causation. SteveBaker (talk) 22:06, 29 August 2008 (UTC)

"That's a totally ridiculous point of view".... is it really? Nimur (talk) 22:27, 29 August 2008 (UTC)

SteveBaker: yes, I know that it is totally ridiculous, but I really wonder why. Why does a government deny psychoactive substances to their subjects (probably because they could do dangerous things while druged, like drunken driving) and at the same time allow it to those in charge of have machine guns, tanks, nuclear armed submarines? 93.132.129.229 (talk) 23:02, 29 August 2008 (UTC)

The stimulants given to military members are available to the US public by prescription. You just have to convince a doctor that you have a need for them. Combat pilots are given then on the theory that they need to stay alert or else they might die. Presumably if you had an equally compelling need (like combating certain sleep disorders), then you could use them too. In neither case are they simply given out for experimentation though. Dragons flight (talk) 23:10, 29 August 2008 (UTC)

These things are given to people rarely and under medical supervision. The people involved are generally pretty fit (mentally and physically) - and it's done for reasons of "national security". That's nothing like a typically unfit drug addict taking them unsupervised - getting them in probably impure form from who-knows-what source - and taking them far too often - for reasons that are deleterious to society in general - not beneficial. SteveBaker (talk) 00:47, 30 August 2008 (UTC)

Your argument is quite good. Actually, I would be more interested in off-pills as I have a longer than circadian rhythm. Do you think I would get a prescription in your country? 93.132.129.229 (talk) 23:19, 29 August 2008 (UTC)

We aren't allowed to answer medical questions on the WP:RD - please seek the advice of a qualified doctor. SteveBaker (talk) 00:47, 30 August 2008 (UTC)

Note also that amphetamines and mescaline are quite, quite different. Pfly (talk) 07:29, 30 August 2008 (UTC)

Then there's nodoze tablets, which are available at most drug stores. They are taken voluntarily and without prescription. Andme2 (talk) —Preceding undated comment was added at 22:46, 30 August 2008 (UTC)

...yes - but active ingradient in NoDoz is caffeine which is not exactly a controlled drug! As I recall, they have about the same amount of the stuff as two cups of good, strong coffee! SteveBaker (talk) 15:32, 31 August 2008 (UTC)

Emit Visible Light by Radio Transmitter

According to article Electromagnetic spectrum, radio waves and visible lights are both electromagnetic waves. The only difference I can see between them is they have different frequencies. So is it possible for a radio transmitter to emit visible light if the radio transmitter can emit radio wave of extremely high frequency? - Justin545 (talk) 09:35, 29 August 2008 (UTC)

In principle, yes. In practice, the required frequencies are unobtainable in any system that would resemble a normal radio transmitter. Dragons flight (talk) 10:10, 29 August 2008 (UTC)

A radio transmitter that emitted visible light it would look very similar to a Incandescent light bulb --Shniken (talk) 14:45, 29 August 2008 (UTC)

Not really. A light bulb's output is a byproduct of heat, not a modulated frequency. — Lomn 17:28, 29 August 2008 (UTC)

Yes, if you use the right equipment. Electromagnetic radiation in radio transmitters is an oscillating field caused by an oscillating current of electrons. That is, we accelerate the electrons back and forth. It's the acceleration in itself that is the trick and another word for electromagnetic radiation caused by the acceleration of a charged particle is Bremsstrahlung. With a current in a wire we only manage radio waves, but when sending the particles round in circles in a vacuum it's a different matter. This is called Synchrotron radiation and you can indeed achieve frequencies from radio waves, into and past the visible spectrum and into ultraviolet and x-rays. EverGreg (talk) 18:31, 29 August 2008 (UTC)

It's a matter of frequency, certainly - but it's easier to think in terms of wavelengths. (Frequency and wavelengths are opposite sides of the same coin here). So let's look at how long the actual waves are:

• TV and FM radio waves are around a meter long...AM radio is out at 300 meters maybe.
• Radar systems and microwave ovens operate at - between 10cm and 1cm wavelengths (there is an elegant experiment involving chocolate chips that lets you measure that in your microwave oven!)
• Waves smaller than a centimeter are called "millimeter band" and are used for short, precise, distance measurements - short range radar - such as the 'reversing sensors' that some cars have.
• Millimeter waves at 1mm are right next to the "far" infrared part of the spectrum - which extends down to "near" infrared at a millionth of a meter. For some reason, we call infrared "light" - not "radio" or "radar" - but it's all the same stuff - it's just a matter of wavelength.
• Infrared light is right next to visible red light in the spectrum. Visible light waves are around half of a millionth of a meter long.

So "radio" waves are about a million times bigger than "light" waves - but they are EXACTLY the same phenomenon - it's just a matter of frequency and wavelength.

To answer the question then: To operate efficiently, Radio antennae need to be about a wavelength long. The antenna on your car is about a meter long - so it can pick up radio waves. The little stubby antenna on your cellphone reflects the fact that it's operating at wavelengths of a few centimeters. So the "antenna" for visible light would be less than a millionth of a meter long! But the systems that make radio transmitters work efficiently simply aren't designed to put out waves that small. The other side of the coin - the "frequency" is to do with how fast the electronics have to oscillate to make waves of the appropriate length. To make radio waves, you only have to oscillate a few million times a second. This is easy to engineer - there are crystals that oscillate at those rates - also you can build all sorts of circuits that'll do that. But as the frequencies get higher, it gets harder and harder to make systems that'll vibrate fast enough. We have computers that run at frequencies as high as 3 to 4 GHz - that's barely as fast as microwaves. Making electronics oscillate faster than that starts to get tough because the size of the electronics has to be small enough to let the electrons get across the circuit in a small enough amount of time. By the time you get into the infrared region, you need to have atoms oscillating - not big things like crystals. So we can't make a 'crystal radio' oscillate anywhere near fast enough to make light. We make infrared by stimulating atoms to vibrate - similarly with visible light. So while light and radio are "the same thing", in practice, it's not just a matter of retuning the transmitter and reducing the size of the antenna to convert a radio into a lightbulb. SteveBaker (talk) 19:10, 29 August 2008 (UTC)

Tiny question for clarity: I thought antennae needed to be half a wavelength long for optimal efficiency? Franamax (talk) 21:24, 29 August 2008 (UTC)

That would be the distinction between a Marconi antenna[1] (archaic nomenclature) and a half-wave dipole antenna; but in modern antenna theory, there are ten million variations on the theme, so "optimal efficiency" may be traded for directionality, bandwidth, narrow-band frequency-specific coupling effects, active control, etc. Nimur (talk) 21:32, 29 August 2008 (UTC)

Yes - and in any case, it's a pretty rough requirement. For the purposes of answering this question we don't need to get into horrible details of the 'black art' of antenna design! You can pick up a perfectly good signal over a wide range of radio or TV channels with a fixed size antenna of roughly a wavelength...but ten times the wavelength or a tenth the wavelength doesn't work nearly as well. The point is that a radio transmitter that's set up with an antenna suitable for AM radio won't make light (which would require an antenna a MILLIONTH of that length). SteveBaker (talk) 21:54, 29 August 2008 (UTC)

Two images of the sky over the HAARP Gakona Facility using the NRL-cooled CCD imager at 557.7 nm. The field of view is approximately 38°. The left-hand image shows the background star field with the HF transmitter off. The right-hand image was taken 63 seconds later with the HF transmitter on. Structure is evident in the emission region.

There have been some experiments in radio-induced airglow or (artificial) aurora, such as this IEEE publication on work performed at the HAARP facility. This is an indirect effect and requires certain ionospheric conditions. The beam is a "High Frequency" radiowave, meaning ~5 MHz, and it is through ionspheric interactions that this energy can be converted in to optically observable light. Nimur (talk) 21:30, 29 August 2008 (UTC)

Here's a link to the Navy's description of optical emissions: [2]. "The exciting result was that by pointing the HF beam directly along a geomagnetic field line, artificial emissions of greater than 200 Rayleighs (R) at 630.0 nm and greater than 50 R at 557.7 nm could be produced. This intensity was nearly an order of magnitude larger than that produced by heating directly overhead." Nimur (talk) 21:40, 29 August 2008 (UTC)

Let's not confuse the OP though. HAARP and the Navy work are NOT a matter of retuning a radio transmitter to broadcast up in the PetaHz (10¹⁵Hz) range! We have no idea how to make a "radio transmitter" that works at such spectacularly high frequencies. The things you are discussing are systems causing secondary effects in the atmosphere. That's not at all what the OP is asking - so let's not muddy the waters! SteveBaker (talk) 22:01, 29 August 2008 (UTC)

I only half-agree. The generation of optical frequencies is a special class of frequency mixing, where the frequency mixer just happens to be a particular natural phenomena / atomic property. Though this effect occurs at high altitude, it's not so very different from using a diode mixer on a circuit board, where a different other atomic effect is responsible for signal conditioning suitable for changing frequency. Nimur (talk) 22:10, 29 August 2008 (UTC)

As you increase in frequency the techniques of producing the oscillations produces less and less power, and amplifiers produce less and less gain until you reach the technology limit around one terahertz. Your antennas will have to be on the same scale as light waves, much bigger than atoms and molecules, and potentially on the same scale as silicon chip technology. But really the problem is generating the arbitrary waveform at the required frequency. As you get to light frequencies the quantization in to photons also takes effect, raising your noise floor. Graeme Bartlett (talk) 08:54, 30 August 2008 (UTC)

Bat vs bird populations

White nose syndrome has had a crippling effect on bats here in the Northeast US. Add to that the heavy rainfall in June and July. It looks like these factors have caused a huge increase in the number of mosquitos in my yard. I normally don't use bug dope but while mowing the lawn just now, I was getting eaten alive! So, how long will it take for the bug-eating bird population to kind of fill the gap that the bats have left? Can I expect a change this year or do I have to wait till next year? Dismas|^(talk) 17:45, 29 August 2008 (UTC)

Wow... It's so quiet, you can hear them buzzing in your ears... Seriously, there aren't any ornithologists in the house? Dismas|^(talk) 00:23, 31 August 2008 (UTC)

Ornithologists study birds - not bats. SteveBaker (talk) 03:14, 31 August 2008 (UTC)

I think you missed the last two sentences of my original posting. I wasn't asking about the bats. Dismas|^(talk) 00:19, 1 September 2008 (UTC)

Is it possible that the current bug-eating bird population has been held in check by a voracious predator? Imagine Reason (talk) 22:35, 6 September 2008 (UTC)

What's with this leaf?

The leaf you see here is covered with round green nodules that look rather like tiny apples. Does it normally look like that? Or is it evidence of some sort of parasite or leaf disease or something else?

Sorry, I don't remember what sort of plant it came from. -- Dominus (talk) 18:45, 29 August 2008 (UTC)

Could be lots of things. See gall. 93.132.129.229 (talk) 19:17, 29 August 2008 (UTC)

It looks quite a lot like hackberry leaf gall. See here [3]Richard Avery (talk) 06:43, 30 August 2008 (UTC)

I'm satisfied with "gall". Thanks, folks. -- Dominus (talk) 02:39, 31 August 2008 (UTC)

It was in fact a hackberry leaf. Thanks again. —Mark Dominus (talk) 13:29, 11 September 2011 (UTC)

Not be exactly with this leaf but quite similar with some mango leaves in my garden. There are some kind of insects implant their eggs in the leaves, making leaf tissue to swell up and the larvae live inside....Ninjaw —Preceding unsigned comment added by 124.120.215.21 (talk) 14:57, 31 August 2008 (UTC)

Freaks

I knew a girl with an additional vertebra in her neck. I knew someone whose uncle had three kidneys. My own mother grew a third tooth in her early 50th. I heard of people who have the heart not only in the right place but also on the right side, instead of the left. All those people are healthy and without examination undistinguishable from those people the anatomy books write about. How common are those uncommon features the like described above? What else can there be? 93.132.129.229 (talk) 19:15, 29 August 2008 (UTC)

It's possible to have an extra one (or an extra set) of many body parts, but often the extra parts are not fully formed. The supernumerary nipple article says the incidence for nipples is 1 in 18 people, but an extra one is often mistaken for a mole. The article on polydactyly (extra fingers and toes) gives an incidence of 1 in 500, but again, most of these are not fully developed. --Anonymous, 19:50, August 29, 2008.

Having the heart on the wrong side is call dextrocardia, that article says it occurs in approximately 1 in 12,019 people. --Tango (talk) 20:18, 29 August 2008 (UTC)

I have that but with all the organs. JessicaThunderbolt 20:24, 29 August 2008 (UTC)

And I wouldn't say it's the wrong side, just the less popular. Sure you have seen alot of dumb faces from new doctors? 93.132.129.229 (talk) 20:36, 29 August 2008 (UTC)

Nah, they all know what it is, but sometimes they get a bit excited as it's the first time they've seen it IRL. JessicaThunderbolt 21:01, 29 August 2008 (UTC)

I'm intrigued...are you left or right handed? And do you think you conform to the stereotype for whichever handed you are? (Wondering whether your brain is also left/right flipped). SteveBaker (talk) 21:40, 29 August 2008 (UTC)

There's a vast range of asymptomatic variation from the 'normal' human body. Perhaps the biggest culprit is the circulatory system, where just about any variation on a theme is possible. Check out the entry in Gray's Anatomy on the aortic arch. Normally three blood vessels (the innominate, the left common carotid, and the left subclavian) branch off the aortic arch. However, variations have been observed with but a single branch and with as many as six branches. (If you go through the 1918 Gray's, you'll find that a large number of sections contain information about 'Peculiarities'.)

This much more recent article notes that external landmarks are unreliable in locating the internal jugular vein in about a quarter of all patients. Moving away from the circulatory system, here's an article about a patient who was missing the upper lobe of his right lung (the rest of the lung just expands to fill the space; he showed no symptoms). In somewhere from 0.1 to 0.7% of people, the gallbladder is beneath the left liver: [4]. TenOfAllTrades(talk) 01:41, 30 August 2008 (UTC)

Standard Units for Quantities of Lumber

Can someone please tell me what is the "standard unit" used for quantities of lumber? My question was triggered by a note taken from Wikipedia:Manual of Style.

"if the text contains an obscure use of units (e.g., five million board feet of lumber), annotate it with a footnote that provides standard modern units, rather than changing the text of the quotation."

Thanks, Wanderer57 (talk) 20:09, 29 August 2008 (UTC)

Board foot says it's a measure of volume, so the standard unit would be metres cubed. --Tango (talk) 20:19, 29 August 2008 (UTC)

1,000 board feet is 2.36 cubic meters. SteveBaker (talk) 21:07, 29 August 2008 (UTC)

"Board feet" estimates the recoverable sawn lumber based on the size of the smaller end of the log, and "log rules" based on old growth timber with 1/4 inch saw kerfs do not accurately estimate the board feet of dimensional lumber recovered with modern thin kerf saws and computerized sawing. The delivered dimensions of nominal 2 x 4 , 2 x 10 inch etc lumber was made smaller in the 1960s, further changing the board feet contained in a tree. A modern 2x4 is 1.5 inches by 3.5 inches, or .656 actual board foot per nominal board foot. The "board feet" in a log changes with definition of a 2x4 and with sawing technology. The cubic meters includes the "total volume of sound wood" including dimensional lumber, chips and sawdust [5]. It is not at all as direct as converting feet to meters. The 1950 conversion was 4.53 m³ per thousand board feet, but conversion factors up to 6.7 m³ have been found to apply. Edison2 (talk) 21:12, 29 August 2008 (UTC)