Wikipedia:Reference desk/Archives/Science/2009 May 26

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May 26

Understanding the Michelson-Morley Experiment

From what I Michelson did the experiment thinking that the speed of light was relative to the aether wind, like the speed of sound was relative to the air. But what does it mean the speed of sound is relative to the speed of the air? Does it work like the headwind-tailwind on a plane? If the sound is in an area with a 10 kph wind does that change the speed of the sound? —Preceding unsigned comment added by 24.171.145.63 (talk) 01:46, 26 May 2009 (UTC)

Yes, the sound will travel faster (and farther) with the wind than against it. Nimur (talk) 02:15, 26 May 2009 (UTC)

As far as what people thought at the time of the Michelson Morley experiment, all speeds (velocities)change with respect to reference frames. For example, on the road, say you move in a car at 20kmph. You see another car moving towards you. By common sense you can tell that the car approaches you faster than if you were not moving, that is the velocities add up. Similarly, it is easily understood that if a car races past you in the same direction as your car, its not moving away from you as fast as it would have if you were standing on the road. This is the Principle of Galilean relativity. This also applies to the speed of sound, cars, and everything which moves at speeds sufficiently lower than that of light. But the Michelson Morley experiment found the speed of light to be same in all directions, even against the hypothetical ether. This violates the Galilean theory. This was resolved when Einstein proposed his Special theory of Relativity, which assumes the speed of light to be constant everywhere in all inertial reference frames. Rkr1991 (talk) 08:30, 26 May 2009 (UTC)

An alternative interpretation of the null result of the MM experiment that had to be considered is that the speed of light does change for a moving observer but that the universe contracts or expands in the direction of movement so that the light speed (i.e. apparent distance divided by time to traverse it) seems constant. Such a hypothetical contraction or expansion would include the observer so would not be observable. Cuddlyable3 (talk) 10:30, 26 May 2009 (UTC)

And is physically indistinguishable from the lack of an ether. Hence Einstein's famously calling the the ether "superfluous." --140.247.251.62 (talk) 16:57, 26 May 2009 (UTC)

There are Newtonian models of light that are consistent with Michelson–Morley and distinguishable from each other and special relativity, like draggable aether and emission theories. Also, Lorentz–Fitzgerald contraction of the apparatus is enough to make Michelson–Morley produce a null result, you don't also need time dilation. This experiment didn't singlehandedly overthrow Galileo—it needs to be considered together with other experiments that ruled out the other possibilities. -- BenRG (talk) 20:11, 26 May 2009 (UTC)

why do dragsters have thick tyres?

Why do dragsters have such thick tyres - eg http://en.wikipedia.org/wiki/File:WheelieBarKennyBernstein.jpg

Is it to make it more stable/support the weight of the engine or do fat tyres improve acceleration (do they typically increase the coefficient of friction between the tyres and the surface)?

Thanks, --118.139.11.63 (talk) 02:30, 26 May 2009 (UTC)

Wider tires produce more contact with the road surface which decreases slippage, and thus improves the ability of the car's engine to push the car forward. If you take it to extremes, imagine trying to drive a car forward using tires as thin as a razor. You'd get almost nowhere. So you want as large of tires as practical, keeping in mind that really large tires also take a lot of power to get moving in-and-of themselves, so there is a tradeoff between being large enough not to slip too much to being too large to move efficiently. --Jayron32.talk.contribs 03:46, 26 May 2009 (UTC)

And to preempt the objections, this is one of many places where the simplified classroom model (surface area doesn't affect friction) is not representative of reality. — Lomn 03:55, 26 May 2009 (UTC)

Both answers above are incorrect. Lomn, the simplified classroom model is actually an excellent model ove a vast range of surface areas and materials. The dragsters tyres are no exception. The real reason the tyres are as big as they are is to keep them from overheating. Jayron is right about one thing, though. There is a tradeoff here and the tyres should be just large enough to avoid overheating but no larger, to minimize drag and inertia. Dauto (talk) 14:11, 26 May 2009 (UTC)

What?! Where did you get this information? They want the tires to be hot, not cold, for better traction. This is why they do a burnout. And the extra width does indeed improve traction. Friday (talk) 18:38, 26 May 2009 (UTC)

Yes, the hot tires work better. But if they get OVERheated, they work worse. Dauto (talk) 05:15, 27 May 2009 (UTC)

As I have previously pointed out (via reference to reliable sources), the high school model is not at all "an excellent model" for tires. -- Coneslayer (talk) 19:21, 26 May 2009 (UTC)

The "high-school theory" is quite good for friction between rigid surfaces. Large tires apply little force to each part of the ground and therefore move it (horizontally) only a little. Thus, the larger the tires and/or the more solid the road, the better the rigid-ground model ought to be. On the other hand, thin tires may at any instant well happen to lie entirely on top of a round pebble and consequently roll whereever. Also, they tend to make deeper grooves into the soil (we're talking about off-road here, right?), during that moving in quite unwanted directions in a quite unpredictable way, not even talking about the energy wasted in digging. — Pt _(T) 19:41, 26 May 2009 (UTC)

In fairness to highschool (and college) teachers I recall being specifically taught that this model for friction only applied to theoretical perfectly rigid objects. APL (talk) 19:49, 26 May 2009 (UTC)

Oh dear - this silly argument again. Dauto is 100% wrong (just like last time - and the time before). The simplified frictional model completely falls apart when it comes to car tyres...as anyone who has ever actually driven a car both before and after putting big fat tyres on it will tell you. Cooling doesn't come into it at all. As Friday says, you really want your dragster to have hot tyres because the hotter they get, the stickier they become. That's why they always do a 'burn out' before they race - it's to get the tyres hot. On Formula 1 tracks, the pit crews actually keep the spare tyres in specially heated jackets specifically to avoid them being cold when the driver comes in to get a new set. I actually race cars for fun (Autocross) - my Mini Cooper has two sets of front tyres (it's a front wheel drive car) one fat pair for track days and one skinny pair for street driving. The 0-60 time is about 2.5 seconds faster on the wide tyres than on the narrow ones. Inertia is certainly an issue - but it's far outweighed by the additional grip. Heating is an issue - but it's the opposite to the way Dauto implies. You actually WANT your tyres to get hot. It's interesting to see the complicated dance Dauto has to go through to explain how come slick tyres (with no tread pattern) have better grip than all-weather tyres that have a tread pattern. The actual reason is because the slicks have more contact area - but the classical/high-school friction equations say that doesn't matter. Pah! SteveBaker (talk) 19:44, 26 May 2009 (UTC)

Steve, we agree on at least one account, this is a silly argument. Would you care to tell us wheather your fat and skinny pairs of tires are acctually made of the same kind of rubber? I doubt they are. Dauto (talk) 04:03, 27 May 2009 (UTC)

I can't prove that they are - but they certainly seem very similar. These aren't racing slicks (which are certainly made of softer composition rubber) - they have treads - they are quite safe in wet weather and are claimed to be street-legal. The reason I don't drive on them all the time is that they protrude out of the wheel-wells of my diminuitive car - and that's NOT street-legal in Texas. Also, they are really expensive and I don't want to wear them out with normal driving. But if the traction they delivered only depended on the rubber composition (as you seem to be suggesting), why would they make wide tyres for track use rather than thinner ones with stickier rubber? Your argument is utterly busted. Pick up a book like the amateur racers' bible: "Speed Secrets" by Ross Bentley. It goes into great detail about how tyres work and how racing drivers 'manage' the contact patch, weight distribution, etc - how to choose the right tyres for the right event, etc. Nobody who drives racing cars would give your version(s) of why wide tyres work the time of day...what you are saying is totally laughable. The honest truth is that the way friction is described in Physics 101 is bullshit out here in the real world. It's a fair approximation for some kinds of materials over some ranges of pressure and temperature - but a horribly incorrect not-even-an-approximation for others. Friction is just too complex. SteveBaker (talk) 16:48, 27 May 2009 (UTC)

As I already said, the high-school (or freshman's) model of friction is in many situations a good approximation! You just must not forget its assumption: you must have two rigid surfaces with no hooks (and the like). Obviously it's well fulfilled for a tram on a railroad (really, a three-cabin tram needs just as long a track to stop as a two-cabin one, although the contact area is much bigger; trains need kilometers for stopping just to avoid excessive forces), but not so well for a car's tires, that are deformed in between the roughnesses and pebbles of the road ("hooks"!). However, don't pour the model entirely down the drain! Another assumption for the simplest formula ($F=\mu N$) is, that the coefficient of friction ($\mu$) is constant throughout the surfaces considered. If it's not, you have to integrate ($F=\iint \mu ndS$, where $ndS$ is an element of normal reaction force). Now, if $n$ is constant, you get simply the $F=\mu N$ formula, but with the average $\mu$ instead. So, with large tires you achieve an averaged good traction, but with thin ones you are sometimes on a really-good-$\mu$ surface (which you naturally even don't notice), at other times on a small $\mu$ (and there you swear). Even more, there is often a correlation between $\mu$ and $n$: the latter is larger where there's something to push against and thus the former is also bigger. Assuming the simplest, linear correlation, we see that now we're averaging over the square of $\mu$! The better it is to have some point on the tire on a bigger-$\mu$ surface, as it contributes even more. — Pt _(T) 22:29, 27 May 2009 (UTC)

Another point about tires (specially soft tires used for racing) is that when heated they become sticky partially crossing over from a friction force into adhesion force (which is indeed proportional to the contact area). So, I guess I concede that the physics 101 friction formula is not an excellent model for a dragster's tires. It is still a fairly good model for street tires nevertheless. Dauto (talk) 03:11, 29 May 2009 (UTC)

What does the "d" stand for?

In article Kinematics#Linear motion, there's a formula:

" Instantaneous velocity (the velocity at an instant of time) is defined as

${\boldsymbol {v}}={\frac {d{\boldsymbol {r}}}{dt}}\ ,$ "

May I ask, what do the "d" stand for? Thank you. 60.0.162.131 (talk) 09:55, 26 May 2009 (UTC) (Matthew 百家姓之四 without signing in)

"Change in". So you essentially have the change in radius over the change in time. How much the radius is changing as time changes. See derivative and differential (infinitesimal), among others. —Anonymous Dissident^Talk 10:11, 26 May 2009 (UTC)

In the context of Kinematics#Linear motion, r is a displacement vector, not a radius. Gandalf61 (talk) 10:24, 26 May 2009 (UTC)

You're correct. Sorry, slip of the mind. —Anonymous Dissident^Talk 10:39, 26 May 2009 (UTC)

The small d is Leibniz notation in differential calculus that means an infinitessimally small change in the variable that follows. Cuddlyable3 (talk) 10:14, 26 May 2009 (UTC)

The 'd' probably comes from the word "difference" (or its equivalent in whatever language Leibniz liked to work in). --Tango (talk) 10:49, 26 May 2009 (UTC)

While the section does try to explain the notation, it seems to do this while going to great lengths not to ever mention the word derivative or link to further reading on the subject; instead the reader is presumed to understand what an "infinitesimally small displacement" is, what an "infinitesimally small length of time" is, and how the one can be divided by the other. I'm not sure this is really productive. —JAO • T • C 11:29, 26 May 2009 (UTC)

Thank you all, Now I clearly understand what does "d" means. I feels Wikipedia is really a warm community. Thanks! Matthew 百家姓之四 Discussion 討論 11:33, 26 May 2009 (UTC)

Oh, may I ask another question? In article Jerk (physics), it says:

"Jerk is defined by the following equation:${\vec {j}}={\frac {\mathrm {d} {\vec {a}}}{\mathrm {d} t}}={\frac {\mathrm {d} ^{2}{\vec {v}}}{\mathrm {d} t^{2}}}={\frac {\mathrm {d} ^{3}{\vec {r}}}{\mathrm {d} t^{3}}}$"

I can understand t², but what is a "d²"? I actually understand "d" as a "Δ", so I get difficulty here. Thank you! Matthew 百家姓之四 Discussion 討論 12:35, 26 May 2009 (UTC)

${\frac {\mathrm {d} ^{2}{\vec {v}}}{\mathrm {d} t^{2}}}$ may be a little counter-intuitive, but it's Leibniz's notation for the second derivative: it actually means ${\frac {\mathrm {d} {\frac {\mathrm {d} {\vec {v}}}{\mathrm {d} t}}}{\mathrm {d} t}}$, that is the rate of change in the rate of change in velocity. It does not actually have anything to do with $t^{2}$. —JAO • T • C 12:44, 26 May 2009 (UTC)

Thank you for your patient explanation. Matthew 百家姓之四 Discussion 討論 13:16, 26 May 2009 (UTC)

It can also be thought of as $\left({\frac {\mathrm {d} }{\mathrm {d} t}}\right)^{2}{\vec {v}}$, which may make the choice of notation a little clearer. --Tango (talk) 14:21, 26 May 2009 (UTC)

Thanks. Matthew 百家姓之四 Discussion 討論 09:31, 2 June 2009 (UTC)

UNIVERSE

WHY ALL THE PLANETS IN THE UNIVERSE ARE ROUND??? —Preceding unsigned comment added by Dasmesh starz (talk • contribs) 11:56, 26 May 2009 (UTC)

Well, I'm not an expert, but i believe the answer comes from gravity. Most planets are very huge(otherwise they aren't called planets) so they have huge mass. Now we all know that because of gravity all masses attract each other, so all the little itsy bitsy particles which make up the planet end up attracting each other, which leads to the planet being under a compressive force, something which pushes itself in from all sides. This results in a spherical shape, as the body then comes under least strain, where all the particles are as close to each other as possible. So, the planets are almost perfect spheres, as other factors also have to be taken into consideration.(I'm guessing the other factors are things like the velocity of the body, the gravity of other bodies, various internal forces, etc.) However, we must note that this does not apply to smaller bodies, like asteroids, which can be seen of almost any shape. This is because the mas is too small for gravity to play a significant role in shaping them, so they are just like chunks of rocks floating around in space.. Also don't forget to sign your posts by placing four '~'s in the end...Rkr1991 (talk) 12:13, 26 May 2009 (UTC)

See also Planet#Physical characteristics and Hydrostatic equilibrium#Planetary geology. —JAO • T • C 12:18, 26 May 2009 (UTC)

Not a very helpful answer, but strictly speaking the correct one: All planets are round because being (roughly) round is part of the definition of a planet! Asteroids are generally not round, because (roughly speaking) they aren't big enough. --Tango (talk) 14:12, 26 May 2009 (UTC)

Why would you call my answer not very helpful ? If there is any specific flaw i can correct it in all my future posts... Rkr1991 (talk) 14:32, 26 May 2009 (UTC)

You misunderstand me. My answer wasn't very helpful. If I were replying to your answer I would have indented my response further. --Tango (talk) 14:35, 26 May 2009 (UTC)

Ceres, the largest of our Solar System's asteroids is also now designated as a dwarf planet because it and only it meets the degree standard for roundness. See List of notable asteroids, and also note that because of rotation and the interaction of other gravitating bodies, the self-gravitation of an astronomical body will generally not result in sphericity, with flattening at the poles and the varying to one degree or another in shape being the total result.Julzes (talk) 15:49, 26 May 2009 (UTC)

There is one that isn't round. SpinningSpark 22:31, 26 May 2009 (UTC)

Earth is a planet, therefore Bizarro World isn't. QED — DanielLC 05:08, 27 May 2009 (UTC)

Health care professional slapping patients

Is there any situation when a health care professional may and need to slap a patient? --Mr.K. (talk) 12:26, 26 May 2009 (UTC)

A slap implies a firm strike with an open hand. I cannot envisage any normal circumstances where this needs to happen. A light slap of the face may possibly be used to rouse a person in danger of slipping into an undesired state of unconsciousness. There are procedures available within the UK healthcare system to express concern about such an occurrence. If a child, elderly person or a person with some other form of vulnerability is involved then an urgent explanation of the circumstances is required. If, on the other hand, this it research for a book the answer is still no. Richard Avery (talk) 14:51, 26 May 2009 (UTC)

No, I only meant in general, for keeping someone awake or wake up someone. I can imagine some situations when it would be useful. Imagine that you find an unconscious person with signs of poisoning. You might try to wake the person up to ask what kind of poison he took.--Mr.K. (talk) 15:08, 26 May 2009 (UTC)

You would generally shake them, rather than slap them, I think. If you want to test someone's response to pain (for example, the work out their score on the Glasgow Coma Scale) the standard way is pressure to the fingernail bed. --Tango (talk) 15:18, 26 May 2009 (UTC)

I've got an auntie who used to be a nurse. As you may or may not be aware, overworked A+E doctors tend to have a *very* dim view of patients who fake unconsciousness. Apparently, it was not unknown for unnecessary 'needle biopsies' of the fingernail bed to be taken in order to test the malingerer's pain response... --Kurt Shaped Box (talk) 20:33, 26 May 2009 (UTC)

There was that Star Trek episode ... —Tamfang (talk) 00:11, 4 June 2009 (UTC)

I've gotten the impression that it used to be customary for doctors to gently slap a baby immediately after its birth to see that it responded properly, i.e. by crying. Was this ever correct and, if so, is it still done? I have no personal experience in the matter. --Anonymous, 16:45 UTC, May 26, 2009.

It is certainly done on TV, and I think it did used to be done in real life as well. As far as I'm aware, it isn't recommended any more. --Tango (talk) 17:04, 26 May 2009 (UTC)

Comedian Rodney Dangerfield said "When I was born, the doctor took one look at me, and then slapped my mother!" Edison (talk) 18:18, 26 May 2009 (UTC)

I've always thought that holding the baby upside down and slapping its tuchis was intended to clear its airway of amniotic fluid, but I realize, now, that I have absolutely no reason for so thinking. Deor (talk) 20:56, 26 May 2009 (UTC)

I don't see how that would work... I, at least, breath out of the other end... --Tango (talk) 20:59, 26 May 2009 (UTC)

Yes, but the ends of babies are closer together; and, anyway, if you could be got to let out a loud wail by a potch on your tuchis, while inverted, I'll bet it would clear your airway. Deor (talk) 21:09, 26 May 2009 (UTC)

I think that they used to slap patients who were hysterical/having some sort of psychotic episode, in order to 'snap them out of it'. --Kurt Shaped Box (talk) 20:33, 26 May 2009 (UTC)

Having worked for too many years in mental health care I can assure you that in the UK nobody of any repute slapped a hysterical (what ever that means) patient or used it to get someone out of a psychotic episode (ditto) If it were that easy why we'd all be psychiatrists. Or maybe there's a critical moment to slap them. Nope, Kurt you've watched Airport the movie, too many times. Richard Avery (talk) 14:41, 27 May 2009 (UTC)

I think you mean Airplane!. Matt Deres (talk) 15:11, 27 May 2009 (UTC)

Yes Matt I do, thanks for that. Richard Avery (talk) 22:00, 27 May 2009 (UTC)

I accept that I may be wrong on this (and I reserve the right to be wrong!) but I do remember reading something somewhere once about the effect of 'percussive therapy' on 'emotional' humans. This would've been way, way, way back if it happened - probably pre 20th Century... --Kurt Shaped Box (talk) 16:29, 27 May 2009 (UTC)

If I were hysterical and somebody came up and SLAPPED me, I can't imagined that it would help the situation any. And from my experience with individuals having psychotic episodes (which is considerable), if you slapped one of them, he or she would get mad, possibly incorporate you into his or her delusional worldview (there's nothing like an unprovoked assault to play into a persecution complex), and, if he or she were predisposed to violence, possibly hand you your sorry tuchis on a silver platter. What's so weird is that (although I'm not a health care professional) I almost slapped my friend the other day because I thought she was slipping into a diabetic coma . . . I didn't, but I did shake her and say her name very firmly and loudly and force her to keep responding until the paramedics came. (She's fine.) Funny, I never thought to do fingernail torture, but if she ever scares me like that again . . . ;) -AJ —Preceding unsigned comment added by 66.215.227.218 (talk) 22:57, 29 May 2009 (UTC)

Bird-flight

How do feathers contribute to bird's ability to fly? I have a general idea, but I am not finding anything about it in the articles. My general idea will send me to fluid mechanics next, but I am thinking it should be prioritized to get this into an article that is obvious to someone less knowledgeable than myself.Julzes (talk) 18:07, 26 May 2009 (UTC)

I find it bizarre that the article Feather does not contain the answer. Perhaps when you've found out, you could add it? ;-) Vimescarrot (talk) 18:16, 26 May 2009 (UTC)

Yes, that is otherwise a very nice article.Julzes (talk) 19:13, 26 May 2009 (UTC)

The critical thing about feathers is that when you push a feather upwards, it kinda unzips and lets air pass through fairly easily - but when you push them down, the little strips lock together to form a fairly airtight seal. This is a really useful thing because it allows a fairly simple vertical cyclic movement to generate lift. Bird flight is very different from aircraft, bat and insect flight. SteveBaker (talk) 19:31, 26 May 2009 (UTC)

Which are all very different from each other. Flight is a fascinating subject. --Tango (talk) 20:07, 26 May 2009 (UTC)

This image

illustrates the "unzip" structure Steve mentioned 71.236.24.129 (talk) 03:42, 27 May 2009 (UTC)

Smoke deflectors on steam trains

These are large plates that (as far as I can tell from pictures) stick out sideways from the front of the engine. The purpose is to keep the smoke from obscuring the driver's view. Efficient engine design made them necessary, because it extracted more heat from the smoke as it passed through the boiler, making the smoke heavier. I have very little interest in steam trains, but certain things about smoke deflectors bother me:

• Wouldn't they cause serious air resistance, perhaps enough to counteract the efficiency savings that make the smoke heavier?
• Wouldn't the plates themselves block the driver's view?
• Why not just connect the engine the other way round, so the chimney is at the back?

81.131.12.157 (talk) 19:20, 26 May 2009 (UTC)

It would certainly improve the view if the engineer and fireman (for Brits, the driver and ?? [still fireman --Heron (talk) 11:10, 27 May 2009 (UTC)]) were in front of the boiler. But where would the fuel and water be stored? The tender was behind the steam engine, and a short path from the coal supply to the boiler was essential. In an oil fired engine, it would have been possible to have the engineer at the front of the locomotive, as on modern diesels. As for efficient engine design eliminating smoke, there was still steam. Steam locomotives at the end in the 1960's still put up a very impressive cloud of smoke and steam. How much was the increase in ari resistance due to the steam deflectors in addition to that of the locomotive, its cab, and the vertical projections of the steam dome and other features? Steam or smpoke deflectors are not mentioned in the Steam locomotive article. Do you have a reference to a book which discusses them? Pictures of locomotives show the smokestack way above the cab windows. Why would the smoke go down instead of up where it would be out of the way? There was a blower which gave it extra upward velocity on locomotives. Edison (talk) 22:56, 26 May 2009 (UTC)

Found the Smoke deflector article. Also Google book search has [1]. The smoke did sometimes drop and obscure the crew's view. Letting the engineer and fireman keep their heads inside the engine and be able to see signals and the track ahead seems a small price to pay for any slight increased drag. Edison (talk) 23:03, 26 May 2009 (UTC)

Smoke deflectors were placed parallel to the air stream - it's hard to imagine them making the vertical-front of the engine much worse than it already was. The front-view from the engine was never that great...but evidently they felt it was worth the small sacrifice in order to keep the smoke out of the way. I also get the impression that most of these were retro-fitted. SteveBaker (talk) 23:04, 26 May 2009 (UTC)

Oh, do they go edge-on to the airflow, rather than flat-on? That makes much more sense. It's kind of hard to judge perspective in the various pictures I've seen (which all look pretty much like the ones in our smoke deflector article), I got the impression they stuck out like ears. Well, if your ears stick out like that. Um. Edison's link took me to a copy of Popular Science with a picture of a highly streamlined locomotive with unique highly streamlined smoke deflectors. I feel generally happier about the whole concept now, thank you. 81.131.57.202 (talk) 23:22, 26 May 2009 (UTC)

Three points. First, the smoke deflectors were typically far enough ahead of the cab that they didn't block much more of the forward view than the boiler itself.

Second, while I've never seen actual numbers on this, it makes sense that it's more efficient to lift the smoke by setting up a diagonal updraft (using smoke deflectors) than by blasting it up vertically (as the older, less efficient engines that did not use smoke deflectors did).

Third, there was one important example of a steam locomotive design with the cab in front of the boiler instead of behind; this was used on the California-based Southern Pacific Railroad. As suggested above, these engines were oil-fired, and as the article indicates, there were some problems with the design, including crew safety in case of a collision and the effect of fuel leaks on traction. However, I think the reason most railways kept the cab at the rear even with oil-fired engines was probably that they wanted them easily convertible in case they later switched to coal, and perhaps a measure of "that's the way it's always been done".

There were also a few railways that tried locomotives with the driving cab in the middle, part way along the boiler. The man driving then had to work in a cramped and hot space, and while he had better visibility on one site, it was even worse on the other side; and he also couldn't communicate with the fireman. Not a successful idea. --Anonymous, 23:48 UTC, May 26, 2009.

Far forward enough not to block the view much, makes sense. Nice links! The camelback is endearingly ugly and awkward. 81.131.57.202 (talk) 00:04, 27 May 2009 (UTC)

Freight engines in use in the U.S. in the last days of steam generally did not have the smoke deflectors in place. A crew behind the boiler in a collision would be scalded to death by the steam, and as dead as if they were in front of the boiler, but in a more painful way. Edison (talk) 05:57, 27 May 2009 (UTC)

In any case, I don't see the advantage in letting the crew think it is safe to have a collision! The driver of that Baltimore & Ohio Railroad camelback appears to have taken his house along for the trip. SpinningSpark 07:50, 27 May 2009 (UTC)

Nobody is saying that it's safe to have a collision! However, if it does happen, you have a better chance of survival with the big mass in front of you than behind you. As for "scalded to death", while that was certainly possible, it was not a likely result of a collision. A locomotive boiler is a pressure vessel that, by the late steam era, regularly contained as much as 20 atmospheres and was tested for more than that; an accident that wasn't violent enough to kill the engine crew by impact would be pretty unlikely to breach it. --Anonymous, 08:54 UTC, May 27, 2009.

A Google book search for locomotive "scalded to death" seems to show that there were more cases of the boiler exploding for reasons such as crown sheet failure and scalding the crew to death than scaldings secondary to wrecks, but some such instances appear. A broken pipe was sufficient to scald one to death, or at least severely. [2], [3], [4], [5], [6], [7], [8]. Steam leaks sufficient to cause severe scalding seem a common consequence of a locomotive wreck, such as a collision or just going off the tracks from a switch error. Then there's the song about the "Wreck of the Old 97" based on a 1903 derailment and crash, where "They found him in the wreck, with his hand on the throttle, scalded to death by the steam." Edison (talk) 23:16, 27 May 2009 (UTC)

cats

Do they really like cheeseburgers? —Preceding unsigned comment added by 86.138.240.52 (talk) 21:08, 26 May 2009 (UTC)

Taken from the cat article: "Cats are classified as obligate carnivores, because their physiology is geared toward efficient processing of meat, and lacks efficient processes for digesting plant matter". Any cat would prefer meat in some form much more than cheese and bread. --131.188.3.20 (talk) 21:20, 26 May 2009 (UTC)

Though it is worth noting that cats can be pretty picky. I've had cats turn down human food that was obviously something that it theoretically would enjoy. (Dogs seem less finicky in this respect.) I'm not sure my old cat would have gone for burger. --98.217.14.211 (talk) 22:14, 26 May 2009 (UTC)

Most cats I've known have liked cheese, though. It is, as BenRG points out below, bad for them, though - adult cats, like most adult mammals, are lactose intolerant. --Tango (talk) 22:30, 26 May 2009 (UTC)

Do Wikipedia vandals really like pie? Deor (talk) 21:26, 26 May 2009 (UTC)

Please don't put this to the test; most cats are lactose intolerant and onion is toxic to cats, and who knows what else goes into a McDonald's hamburger that isn't tested on felines. -- BenRG (talk) 21:38, 26 May 2009 (UTC)

I think cheese doesn't contain much lactose, because the lactose is in the whey, which is removed. Also there is no mention of their alleged lactose intolerance in the cat article (although there is something about fatty acids), and there is a picture of "a very young cat being fed on milk"; and cats are famously portrayed as drinking milk - have they been given diarrhea all throughout history? - and of course they are mammals - does cat milk not contain lactose? Basically I don't believe you, except the bit about the onion, which I am going to accept unquestioningly and tell to other people. 81.131.57.202 (talk) 22:55, 26 May 2009 (UTC)

Adult cats are lactose intolerant. Most mammals lose the ability to digest milk after infancy, so there is no need to mention it specifically in the cat article. Humans are the exception to the usual rule, although even we only evolved to keep the ability very recently in evolutionary terms and there are plenty of people that don't have that mutation. --Tango (talk) 23:12, 26 May 2009 (UTC)

Oh yes, that rings a bell actually, you're right. Lactose intolerant people are not weird, it's those of us who can digest it who are the mutants, supposedly. Bit odd to lose an ability in adulthood, though, for no reason. I can only assume it's a side-effect of gaining some other advantage. 81.131.57.202 (talk) 23:27, 26 May 2009 (UTC)

The reason mammals lose the ability to digest milk is to ensure that one litter of offspring are properly weaned before the next litter comes along. The mother can only produce so much milk and if older offspring were competing against the newborns, that would be highly detrimental to the younger animals. Hence, all mammals have developed a system that makes them unable to digest milk past a certain age - and to have major discomfort should they try to do so. It is thought that humans were just like all of the others in that regard until perhaps 5000 years ago when we started to farm dairy animals such as sheep, goats and cows. Since we have language and education and societal pressures to ensure that babies are weaned off of their mother's milk soon enough - we no longer need the genetic shutting off of the lactose pathway. To the contrary - if you imagine a family who farm a few goats and who are lactose intolerant - then in times of famine - they'll be tempted to slaughter the goats for meat...and then they are in deep trouble. The family who happen to be lactose tolerant into adulthood can get their nutrition from milk, butter and cheese and keep the goats alive through to the next time of plenty. Guess who does better in the long term? It seems that 5000 years ago, we started to evolve the ability to drink milk in adulthood - but increasing civilisation means that very few people indeed survive preferentially because they can drink milk - so the evolutionary pressure to become lactose-tolerant has gone away - and here we hover, partly evolved, partly not.

Uh-huh. Do lactose-intolerant adult cats like to drink milk? If so, then the inability to digest it clearly doesn't work as a way of getting older kittens to stop suckling, since it doesn't make them actually stop drinking it, just gives them a stomach upset. I'm also unsure what animal rights logic says an animal should be prevented from causing itself harm in a way it apparently enjoys (all of which is anthropomorphic anyway, the harm and the enjoyment). Also, as a third point, "unable to digest" must be shorthand for something a bit more complicated, because we eat things we can't digest all the time, without any problem: when it's called "roughage", we're encouraged to eat it, and there must be indigestible liquids which similarly pass straight through without causing pain. Or indigestible components of otherwise digestible foods. Must happen all the time, harmlessly. 213.122.66.195 (talk) 17:47, 27 May 2009 (UTC)

Actually that last point is answered below in the question about gulls (and in the lactose intolerance article, which I should have read properly) - it's gut bacteria feasting on the undigested milk-sugar that cause the trouble. 213.122.66.195 (talk) 17:59, 27 May 2009 (UTC)

Reference reference reference reference reference reference. I hope this helps you to believe that most cats, like most mammals, like most humans, are lactose intolerant and diarrhoea is a common side-effect of feeding a grown cat with cow's milk. 80.41.116.160 (talk) 23:23, 26 May 2009 (UTC)

The first five of those references might just be echoing a myth, since they just seem to blankly say, in gentler terms, "CATS ARE LACTOSE INTOLERANT ALRIGHT SO STFU", but I like the last one, it looks science-y. I like the term "vetinary technician". Also it confirms that "cow milk has higher levels of lactose than does cat milk", and explains about lactase. Still, none of them mention cheese. I think cheese is OK for cats, by reason of being low in lactose.81.131.57.202 (talk) 23:46, 26 May 2009 (UTC)

I tried to provide a variety, to suit whatever your doubts were that cats are like all other mammals. The third link, for example, links to advice from the RSPCA. Cheese is lower in lactose than milk; do you have a particular reason for thinking that the levels are low enough not to cause a problem for cats? Like most things, it will vary from cat to cat and by amount of cheese. 80.41.39.25 (talk) 01:06, 27 May 2009 (UTC)

I would assume that his particular reason for thinking that the levels are low enough to not bother a cat is that because you can get cheeses with zero lactose. It's not even a specialty item. Aged cheddar and sharp swiss are both commonly recommended to people who can't eat lactose, and both would be excellent on a cheeseburger.

Personally, I'd be more concerned about the roll. Does it still count as a cheeseburger if it's not served on a bun? Normally you could depend on a cat to simply eat around a bun, but if it soaked up the grease from a freshly cooked cheeseburger, I wouldn't bet on it. APL (talk) 01:32, 27 May 2009 (UTC)

You can get cheeses which are zero lactose, so those would probably be fine, but that isn't all cheese. Most cheeseburgers I've seen have come with those processed cheese slices; what are the lactose levels in those? Does it vary depending on the manufacturer and variety? I'm not saying you couldn't carefully construct something that would count as a cheeseburger and which a cat could safely eat, but I'm not convinced a random generic cheeseburger would be a good idea. 80.41.39.25 (talk) 01:43, 27 May 2009 (UTC)

You're right that American Cheese is probably the most common cheesebuger cheese thanks to McDonalds, Burger King, etc. But most sit-down restaurants (nothing fancy, your local diner will do) that serve cheeseburgers will offer one with cheddar or swiss. You couldn't trust the cheddar, though unless it specifically says "aged cheddar", and I can't seem to find any sources that say whether or not "mild swiss" has any lactose in it, so you'd really have to ask the chef.

But who are we kidding? What kind of diner is going to let your bring a cat? If your heart was set on giving your cat a cheeseburger you'd want to set up the old barbecue grill and do it yourself. Aged cheddar or sharp swiss are perfectly legitimate burger toppings, so I don't feel that's a cheat at all. I don't know what sort of other toppings are safe for cats, but they're purely optional and the cat probably wouldn't appreciate them anyway.

I'll bet the amount of grease in the sandwich would be the biggest concern to a vet. APL (talk) 02:51, 27 May 2009 (UTC)

Here is a vet who says that, like with all other mammals, most cats do not retain the ability to digest lactase into adulthood, therefore giving an adult cat milk may lead to diarrhoea. Here is another vet who says the same, with less science. Or how about this? —Preceding unsigned comment added by 80.41.39.25 (talk) 01:16, 27 May 2009 (UTC)

The humour in "I CAN HAZ CHEEZBURGER" originates from its implication that the depicted cat desires a food that normally humans and not cats desire, in the same way that "INVISIBLE BIKE" is funny because people ride bikes, not cats. Dcoetzee 21:46, 26 May 2009 (UTC)

Also, the cat can't spell. Which is funny. --98.217.14.211 (talk) 22:13, 26 May 2009 (UTC)

I wonder how many generations of people cluelessly feeding cats saucers of milk or cream will cause them to gain the ability to digest milk. I have no idea how reliable it is, but I've heard anecdotal evidence that some adult cats are fine with it. I suggest that cat breeders start selecting for those cats so as to bring reality more in line with Tom&Jerry cartoons. APL (talk) 01:21, 27 May 2009 (UTC)

Unless the cats who do not drink the provided milk die off or breed less, that scenario will never produce a selection pressure. If a statistically significant number of cat owners fed only milk to their cats, only those who adapted would survive and reproduce; and lactose tolerance would evolve into the gene pool. Because most owners only provide milk as a "supplement," this will not happen. When cats choose not to drink milk, it does not impact their capability to breed. Nimur (talk) 01:45, 27 May 2009 (UTC)

I was imagining the people, in books and cartoons, who leave a saucer outside their back door for the neighborhood stray. But I don't suppose that's anywhere near common enough in real life to be a useful food source powerful enough to cause a selection pressure towards cats that can take advantage. Once again cartoons and books are more interesting than real life. APL (talk) 02:51, 27 May 2009 (UTC)

It is best to feed pets standard pet food. The standards set up by the AAFCO are light-years better than the way the FDA is geared to handle human food.Julzes (talk) 03:25, 27 May 2009 (UTC)

Having recently acquired a couple of cats, I noticed that you can buy "cat milk"; I assume there aren't cat dairy farms out there, so it must be synthetic/manufactured from cow's milk. If you were really dedicated to reproducing the meme, you could probably make your own cheese from this. However, according to Cats Protection, the milk is very high in calories ([9]), although that may not be a concern if the cat is eating burgers anyway. --Kateshortforbob 11:30, 27 May 2009 (UTC)

Hahaha! When I first saw my mother feeding 'cat milk' to her moggy, my first response was "They've started commercially milking cats now?"... ;) --Kurt Shaped Box (talk) 12:01, 27 May 2009 (UTC)

That is not far from the truth. Zoo owners know that nursing cat mothers are remarkably tolerant of unrelated baby animals in their litters, even orphans from different species. Cuddlyable3 (talk) 19:12, 30 May 2009 (UTC)

60m

what are the chanels in 60m —Preceding unsigned comment added by 74.99.36.208 (talk) 23:30, 26 May 2009 (UTC)

Do you mean to ask which radio frequencies have wavelengths close to the 60 meter band? That would be HF radio or Shortwave. If you want a specific broadcaster, you will need to give a more precise wavelength and/or frequency, and probably a region as well (although shortwave does propagate almost globally). Nimur (talk) 00:13, 27 May 2009 (UTC)

And if you're hamming, take a look at this FAQ. The NTIA has granted five 2.8 kHz channels, (5332, 5348, 5368, 5373, and 5405 kHz center frequencies), for amateur use in the United States. Regulations may vary in your region. Are these the channels you were asking for? Nimur (talk) 00:17, 27 May 2009 (UTC)

Adding R-values for bulk ceiling insulation not allowed

I'm having a problem with this. I'm told that laying 2 layers of R 2.0 (S.I units) ceiling insulation wont give R 4.0. I understand this would be the case if the insulation (uncoated polyester) became compressed, or if the batts were not uniform in composition. The reflective value is not an issue as the standard the work is done to in this case is concerned only with heat transfer from the rooms to the roof (i.e winter insulation). The proposed technique is laying the first layer (10 cm thick) between the joists in the ceiling, and the second layer at right angles on the top completely covering the first layer and the joists as well. The joists themselves are rated R 0.6-0.8. The standard (AS 3999 - dont bother looking it up as you have to pay for it) allows R 4.0 (20cm)laid between the joists (not covering them) which I feel certain would give a lesser effective insulation than the cross-laid technique. R 4.0 insulation costs slightly more than two layers of R 2.0 This is a heavily relevant question as the Aust. Government has a massive rebate for ceiling insulation and many people are getting their ceilings done for the first time. I will check for answers here for several months, so late replies very welcome. Polypipe Wrangler (talk) 23:57, 26 May 2009 (UTC)

Please check the "thickness" section in R-value (insulation). I do not know why they do not add, but apparently they do not. -Arch dude (talk) 00:29, 27 May 2009 (UTC)

As I understood R-value, putting two layers of R 2.0 would yield an equivalent R value of 4.0. Of course, R-values are approximate anyway, within a very wide tolerance of the manufacturing and installation procedure. Nimur (talk) 01:29, 27 May 2009 (UTC)

I'm not sure of the definition of R-value - but think about how insulation actually works: If you spend $100 on heating bills and one layer of insulation were to (say) halve the heat lost from the room - a second layer would halve the half that the first layer let though - so the first layer would save you $50 - but the second layer only saved $25. Every additional layer would save you less and less. This is a multiplicative effect. If they added - then the second layer would have to block every last drop of heat loss that the first layer missed...and that's just not reasonable. SteveBaker (talk) 03:58, 27 May 2009 (UTC)

According to US Department of Energy's Insulation fact sheet, "In calculating the R-value of a multi-layered installation, the R-values of the individual layers are added." While this is only an approximation (because of second order effects like compression of the lower layers that reduces their effectiveness), it seems to be a reasonable one. Are the regulatory recommendations any different in Austria (Australia ?), or is it possible that you were just misinformed ? Abecedare (talk) 04:13, 27 May 2009 (UTC)

I don't see why R values of thermal insulation would not simply add like Ohms of electrical resistance. Edison (talk) 05:45, 27 May 2009 (UTC)

Don't know the answer but I would suggest a radiant barrier as well as some insulation can work better in the attic than just using twice the amount of insulation. Dmcq (talk) 09:48, 27 May 2009 (UTC)

R-values for plasterboard ceiling and tiled roof are listed in AS 2627.1-1993 (not available on internet). Then they are added (including air layers) to get a total R-value (0.35 in this case). This is the same technique used as shown above by Edison. The big rebate on installing insulation also requires that the residence have "negligible" existing insulation defined as at or below R 0.5. The whole rebate is listed at www.environment.gov.au/rebates/ . Trying to second-guess the rebate people's interpretation of the existing R-value of a residence is difficult. Looks like technically any evenly spread layer of cellulose loose-fill deeper than one inch (R 0.52) would mean no rebate, or with the tiled roof above even just over R 0.15 of added insulation would make the rebate condition invalid. Polypipe Wrangler (talk) 00:11, 31 May 2009 (UTC)

Last news, a both a teacher of insulation installation and the rebate people have confirmed that it is OK to use 2 layers of R2.0 insulation as long as sighting sticks are placed so people can find the joists to walk on. (Australia) Polypipe Wrangler (talk) 23:53, 24 September 2009 (UTC)