Wikipedia:Reference desk/Archives/Science/2013 March 11

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March 11

Why does water spray out of a tap quicker if you almost completely cover it with your thumb?

The title pretty much says it. I was wondering because I always assumed it increased the pressure but thinking about it it shouldn't affect it because with a smaller volume exiting the force will be proportionally less due to constant pressure.--Gilderien Chat|List of good deeds 00:23, 11 March 2013 (UTC)

Read the article Bernoulli Principle. 24.23.196.85 (talk) 00:34, 11 March 2013 (UTC)

Strictly speaking, Bernoulli's principle is not relevant because it is only valid in situations where fluid friction is zero. In flow in a pipe, fluid friction exists throughout the flow profile across the pipe's diameter. See my response below regarding fluid friction. Dolphin (t) 02:07, 11 March 2013 (UTC)

With a rapid flow of water there is a substantial amount of fluid friction which exerts a shear force on the water in the pipe, retarding its speed and causing the pressure to fall along the pipe. (See Boundary layer.) When you reduce the flow of water by using your thumb there is less fluid friction and consequently less fall in pressure along the pipe. The pressure of the water at the end of the pipe is highest when the flow of water is almost reduced to zero. Torricelli's law explains why the water sprays out quicker and higher when the pressure of the water at the end of the pipe is highest. Dolphin (t) 01:45, 11 March 2013 (UTC)

The correct answer is simpler than the answers above. Friction does indeed affect the exit speed but that speed increases even if friction is completely negligible. The speed is given by dividing the flow by the cross section area of the pipe. If you reduce the latter, the speed will increase. Dauto (talk) 15:06, 11 March 2013 (UTC)

I'm pretty sure that's wrong. In principle the utility company supplies a constant pressure to the big pipe to your home. Assuming no friction from there to the tap is equivalent to assuming the pipe length is zero, and your thumb is blocking the utility company's supply at its source. When you do that you will just get proportionally less water. In practice I suppose the flow rate and pressure will change slightly, but it will be averaged over many homes. The water can't know to flow at twice the speed through your opening specifically if you block half of its area. -- BenRG (talk) 17:14, 11 March 2013 (UTC)

Dauto's explanation is correct, its an equal volume through a smaller cross section requiring a faster speed. If the water pressure's not too high then you can get to the point of actually blocking the flow by pressing hard enough which would be what BenRG is suggesting--in effect turning of the tap, just as with a valve. μηδείς (talk) 18:11, 11 March 2013 (UTC)

You can also experiment with this if you have an adjustable flow shower head. At one setting it will offer a slow flow through all the spigots. Tighten it a little and you will get the same flow but at a faster speed through fewer spigots. Tighten it some more and you'll reach a maximum speed with the total flow decreasing, eventually to zero. But you can always adjust it to get a full flow at a faster speed with a certain amount of restriction, but no more. μηδείς (talk) 18:19, 11 March 2013 (UTC)

I don't see why BenRGs point is incorrect, it is along the lines I was thinking. Will the "narrowing" caused by my thumb increase the pressure at the end? --Gilderien Chat|List of good deeds 22:44, 11 March 2013 (UTC)

If there's no friction, a narrowing of the pipe has to be accompanied by a decrease in pressure just because of energy conservation (the water moves faster in the narrower pipe, so its kinetic energy is higher, and that extra energy can only come from the pressure). In practice there is a substantial pressure increase when you block the end of a garden hose, for example, but that's because there's less friction in the hose (as Dolphin51 said). -- BenRG (talk) 00:21, 12 March 2013 (UTC)

It's true of course that if you narrow the aperture while keeping the flow rate constant then the speed will increase. But there's no reason for the flow rate to remain constant, and in most cases it doesn't, as you can check by doing the experiment. The water company supplies a fixed pressure, not a fixed rate of flow. -- BenRG (talk) 00:21, 12 March 2013 (UTC)

Dauto's simple explanation makes no sense. The water company supplies a pressure that varies very little, not a fixed rate of flow. The thumb over the end of a garden hose is a classic experiment any student can perform at home to demonstrate the existence of fluid friction. In an hydraulics laboratory the same demonstration is performed using pipes of different lengths, different internal diameter, and different internal surface roughnesses; a pressure gauge is at each of the upstream end of the pipe and the downstream end. Plotting pressure difference versus flow rate for these different pipes yields a lot of useful information but it is all an illustration of the phenomenon of fluid friction. Dolphin (t) 04:59, 12 March 2013 (UTC)

Thank you, I now understand.--Gilderien Chat|List of good deeds 20:20, 12 March 2013 (UTC)

Reynolds number and Laminar flow. --Kharon (talk) 05:16, 13 March 2013 (UTC)

Resolved

Catalan Talgo

Did the passengers have to disembark for the gauge change at the Spanish border, or was the operation performed with them still aboard the train? 24.23.196.85 (talk) 00:41, 11 March 2013 (UTC)

Cosmic ray

I know cosmic rays exist in interplanetary space and interstellar space. Do cosmic rays exist in the intergalactic space? --PlanetEditor (talk) 06:36, 11 March 2013 (UTC)

I don't see why not. Plasmic Physics (talk) 06:41, 11 March 2013 (UTC)

• Yes, since active galactic nuclei are a source of cosmic rays. -- Scray (talk) 07:01, 11 March 2013 (UTC)

That is still speculation. Existing evidence suggests supernova remnants are the origin of cosmic rays (90% protons and 10% atomic nuclei and electrons). [1]

If supernova remnants are the origin of cosmic rays, it will be present in the interstellar and interplanetary medium within a galaxy. But will it be able to escape the galaxy? --PlanetEditor (talk) 07:37, 11 March 2013 (UTC)

Why not? Plasmic Physics (talk) 07:42, 11 March 2013 (UTC)

If we want to take a strict observationalist approach, we can trivially state that we have no idea, because we have never sent a probe to experimentally measure the presence or absence of cosmic rays in extragalactic space. Or, we can take the more useful, albeit less provable, stance: we have a pretty good idea that many high-energy things originated outside our galaxy. One of my favorite muon detectors, AMANDA, was intentionally "pointed down" so that it would detect incident radiation that was not along the Ecliptic or the galactic equator. That implies, in my opinion, that the neutrino sources would be extrasolar and probably extragalactic. (Though, this 1998 paper suggests that South Pole Station was one of many worldwide detectors and could be used for holographic triangulation of neutrinos from any direction; and AMANDA II had improved angular resolution for mapping purposes; but, to steal a quote, the full scientific implications are far too broad to discuss in this limited forum. Nimur (talk) 08:14, 11 March 2013 (UTC)

Thanks. --PlanetEditor (talk) 08:33, 11 March 2013 (UTC)

Nimur, perhaps a followup question. It occurs to me that if the rays are coming from within our own galaxy, there should be some kind of relationship between the trajectory with which the ray reaches the Earth, and the density of rays coming along that trajectory, that makes sense given the number of potential intragalactic sources along any given trajectory. Is any such thing elucidated by the available evidence? Someguy1221 (talk) 08:46, 11 March 2013 (UTC)

The second paper I linked talks about a knee-point in the spectrum at 10¹⁵ eV. Below this energy, the authors believe neutrinos are generated by point-sources - supernovae, "micro quasars"... - so the incident raditation is expected to have a directionality. Above this energy, there are far fewer events, or at least far fewer detections, so statistics are not as clear; but it seems possible that these very-high energy neutrinos are not generated by point-sources. If so, there are a few questions about their origin that are unanswered: we expect the cosmic microwave background radiation to be much lower temperature based on everything we know about the evolution of the early universe. My response, as an enthusiast for muon detectors, is that we clearly need to fund and build more such detectors so we can collect better data; I don't think there are enough observations to be really really sure of very much about these high energy incidents. Nimur (talk) 15:40, 11 March 2013 (UTC)

There is now strong evidence that the ultra high energy cosmic rays come from Centaurus A, see e.g. here. Count Iblis (talk) 12:47, 11 March 2013 (UTC)

Chemical egg

What are those things that look like glass boiled eggs, filled with various reagents, resting in an egg cup? Are they some sort of ampoule? Plasmic Physics (talk) 07:16, 11 March 2013 (UTC)

Possibly. Where have you seen them? Can you post an image of one of "those things" to give us a better idea of what you have in mind?--Shantavira|^{feed me} 16:50, 11 March 2013 (UTC)

[2] Plasmic Physics (talk) 21:49, 11 March 2013 (UTC)

[3] Plasmic Physics (talk) 21:53, 11 March 2013 (UTC)

They look to me like round-bottom flasks (okay, actually a pear-shaped flask - [4], but at least for organic synthesis use those fall into the general "round-bottom flask" category, at least when used in semi-microscale chemistry) that have been stoppered (with a specialized stopper) and inverted. Laboratory flask mentions "Powder flasks, for drying of powdered substances, pear shaped, with socket" which may be more apropos, but I've never heard of those before, the link redirects to Musket, and searching the term either returns nothing related (in Sigma-Aldrich's search engine) or black-powder related results (in Google). -- 205.175.124.30 (talk) 18:18, 12 March 2013 (UTC)

That makes much more sense, I didn't imagine inverting them. Plasmic Physics (talk) 22:21, 13 March 2013 (UTC)

What are these lights?

What are those flashes of light seen in this video at 1:24, at 1:28 to 1:29 and again at 1:52. --PlanetEditor (talk) 08:27, 11 March 2013 (UTC)

Some of those flashes are lightning, and others are errors of exposure in the photograph, either due to operator error or due to digital post-processing. Previous montage-videos and time-lapses from the ISS have used long exposures and multiple captures to produce the high dynamic range you see in the final video imagery. Here are more videos, including videos with less post-processing than your link: ISS Crew Earth Observation videos from NASA Johnson Space Center. The video linked in the original question was produced by a film student, not by NASA; and was composited from NASA's image database using what are termed "browse quality" photos. FAQ #2: "Because of the number of images that are added to our database each day, we cannot do publication-quality color corrections on each image. For some scientific purposes those corrections even destroy information (even though they make the picture look prettier)." Nimur (talk) 08:37, 11 March 2013 (UTC)

Freezing point

I just read our article on Melting point (to which Freezing point redirects). I understood some of it, but not too much, which is unsurprising given how little Science I got away with studying at school. From what I could gather, the article only mentions pressure as being a factor in setting the freezing point of a substance, which seems like a big gap, as different substances at the same pressure (say water and mercury) will have different freezing points.

Some questions - please be gentle with the layest of laymen:

1. Why do different substances have different freezing points? Is it their physical properties, chemical properties, both, something else?
2. I know that salt lowers the freezing point of water. What substances that might lie around a typical house would raise it? And if so, is there anything that is edible?
3. I'd guess that British tapwater would have a different freezing point than distilled water. What's the difference and what additives are making the biggest contribution to that difference?

Thanks.

Yours curiously (I always liked the curiosity bit of Science, just not the intellectual rigour/need to remember things bits) --Dweller (talk) 11:01, 11 March 2013 (UTC)

1. In broad terms, there are two competing set of forces that hold subnstances together. Intermolecular forces are the electrostatic forces between the positive and negative charges. Thermal energy is the energy of motion that tends to want to encourage molecules to fly apart. If the thermal energy exceeds the energy of the intermolecular forces, the particles that make up the substance fly apart, and the substance will be a gas. If it is the other way (intermolecular exceeds thermal) then the substance will be a condensed phase (either a solid or liquid). The actual process of melting itself (the transition from solid to liquid) is mostly based on a specific types of thermal energy: those of molecular vibration and rotation. The third mode of thermal energy is "translation", which marks the distinction between gases and the condensed phases of solids & liquids. All of the various modes of thermal energy together are known as a molecule's degrees of freedom, and those degrees of freedom are important towards understanding properties like this. Melting itself is a far more complex and difficult to model behavior, but that's roughly it.
2. Roughly speaking, any substance you dissolve in water will lower its melting point. That's because freezing-point depression is one of the colligative properties, which primarily depend on the number of dissolved particles, but not (to a first approximation) their identity. That is, the fact that anything is mixed in the water will cause its freezing point to lower, but the amount of lowering isn't dependent on what that substance is, only on how much there is. Now, there are some liquids which if you add enough of them to water, may raise the freezing temperature, but what you have there is a eutectic system, and at that point what you would have isn't that substance dissolved in the water, but rather the water dissolved in the other substance, and then we'd be basing our colligative relationship on that rather than on a water-based solution.
3. Tap water will have a very marginally lower freezing point than absolutely pure distilled water. Even the worst tap water is still very mostly water; the stuff that isn't water in tap water can be measured in the parts per million range, which will have a very small effect on the freezing point, probably not noticeable on the average household thermometer. --Jayron32 12:42, 11 March 2013 (UTC)

(ec) Q1. All substances that we can see are of two types: elements and compounds. A compound is a substance made up of multiple elements. Water is a compound because it is made up of oxygen and hydrogen. In nature, most of the substances that you see or feel everyday, such as water, oxygen etc. are compounds. Only the noble gases and noble metals are found in elementary form or monoatomic form (i.e. they consists of one atom). Here we will be dealing primarily with compounds.

Any substance, whether it is an element or a compound, is composed of particles. In case of elements, this particle is called atom. In case of compounds, this particle is called molecule. A molecule is made up of two or more atoms. (The atoms are made up of multiple subatomic particles, but that is not relevant to this discussion.) This particles are attached to each other by a force or attraction. This is called chemical bond. Without chemical bonding, the particles will be separated. If the particles are separated, then the substance will cease to exist.

Now, when you heat a substance (say water), then what happens? When the temperature reaches 100 degree Celsius, the molecules within water possess enough energy and they overcome the intermolecular attractions that bind the molecules. When they overcome the intermolecular attractions, the distances between the molecules become greater. This turn the liquid into gas. In solid, the distances between the molecules are smallest, in gas the distances between molecules are greatest.

Now, what we can see? The freezing point or melting point of a substance (whether an element or a compound) is dependent on the strength of the bonding between the particles. So if the bondings are stronger, you will need more energy (heat) to break them, so the boiling point rises. If the bondings are weaker, you will need less energy (heat) to break them, so the boiling point falls.

I explained the mechanism in terms of boiling point. In case of freezing point, a liquid turn into solid. So if the bondings are strong, melting point will increase and freezing point will decrease. If the bondings are weak, melting point will decrease and freezing point will increase. Helium has weakest bonding. This is why its boiling point is lowest, near absolute zero.

This is the explanation why different substances have different freezing points, melting points and boiling points. --PlanetEditor (talk) 12:49, 11 March 2013 (UTC)

Thanks, chaps. Enlightening. I particularly liked Jayron's answer to Q2 and PlanetEditor's excellent "keep it simple without patronising" style of writing. One last thing - am I right that the information was missing from the article, or was it there, but just impenetrable to me? --Dweller (talk) 12:54, 11 March 2013 (UTC)

Actually, it's there in the section labelled "Carnelley's Rule", which I've never heard the name before, but knew the principle well. The deal with that "Rule" is that molecules which are more symmetrical don't have as many "degrees of freedom" (see above), so have less modes by which to vibrate. Consider the geometry of something like a sphere, versus a cylinder, versus say a human body. With a sphere, you have zero vibrational modes; the sphere cannot vibrate because there are no parts that can vibrate relative to each other. In a cylinder, you have one vibrational mode: the cylinder can vibrate in-and-out along the axis between the molecules at the end. In the human body, there are LOTS of vibrational modes: every limb can move in and out, around, bend at angles, etc. The same is true of molecules. Furthermore, the more symmetrical a molecule is, the less ways it can be arranged, so the more efficiently you can "pack them" together. Spheres pack very efficiently, cylinders less so (because cylinders arranged at angles won't match up positive and negative bits well) while something shaped like a person would be a complete nightmare to get to randomly arrange properly. Because of both of these factors, more symmetrical molecules (by definition, those with less vibrational degrees of freedom: those are coincident properties) are those that will melt at higher temperatures, all other factors being equal (such as molecular weight, polarity, molecular volume, etc.) --Jayron32 17:33, 11 March 2013 (UTC)

Missing quantity

Consider an underground water source whose free surface is 60 meters below ground level. The water is to be raised 5 meters above the ground by a pump. The diameter of the pipe is 10 cm at the inlet and 15 cm at the exit. Neglecting any heat interaction with the surrounding and frictional heating effects, and assuming a steady flow of water at a rate of 15 liters per second, and that the water remains at atmospheric pressure and temperature. Determine the power input at the pump.

I have this equation

${\frac {dE}{dt}}={\frac {dQ}{dt}}+{\frac {dW}{dt}}+{\stackrel {\circ }{m}}(u_{2}+P_{2}v_{2}-u_{1}-P_{1}v_{1}+{\frac {1}{2}}(V_{2}^{2}-V_{1}^{2})+g(z_{2}-z_{1}))$

Where we need to find ${\frac {dW}{dt}}$, of course. I believe all of those quantities are given or are easily derived, except I don't know how to work out $u_{2}-u_{1}$. How do you do that?

150.203.115.98 (talk) 14:26, 11 March 2013 (UTC)

get the flow (in cubic meters per second) and divide it by the cross section area of the pipe (in squared meters) to get the speed (in meters per second). Dauto (talk) 14:53, 11 March 2013 (UTC)

That's $V_{2}$ and $V_{2}$. I suppose I should have said what these symbols meant. $u_{2}$ and $u_{1}$ are specific internal energy. 150.203.115.98 (talk) 23:45, 11 March 2013 (UTC)

In that case their difference vanishes since all heat is considered negligible. Dauto (talk) 14:33, 12 March 2013 (UTC)

productivity of 120 hour weeks

my personal impression is that if pressed a single person can perform the work of 5 (the skeleton crew of a company), including marketing business sales design engineering biz dev (contacts and so forth) and so forth for a very short period of time.

is this a fallacious impression?

or could three things work together here:

1) Granted productivity must drop off precipitiously after 40 hour. But perhaps for some kinds of "work" even a productivity of 0.01 person-hours per hour is enough, for example when waiting for an email response that must simply be OK'd once received. Either someone is sitting there waiting or they're not. Thus perhaps some of the work of the 5 people can be interleaved as interrupts and does not require a full amount of time added to the workload.

2) Perhaps there is some kind of "economy of scale" that comes from many, many hours. That is to say, perhaps 20 hours of trying to close a deal are 80 times more effective (in an all-or-nothing situation) as 3 hours of doing that (rather than only seven times as we might expect based only on the time). If so then the precipitious drop in productivity - a 97% drop in productivity, say - between hours 112-120 in the week, could still, leave the remaining 3% of productivity highly productive due to this reason.

3) Perhaps there is some kind of "economy of scale" that can come from serializing work that would otherwise (in a larger team) be parallel, or bringing all aspects (e.g. design and programming) into the same brain: that is, there is now no interprocess communication or delay waiting for someone else to acknowledge something, nor is there repetition of:

- Several people waiting one after the other

- Blocking conditions that create a bottleneck

- Repetition of the same information being read, stored, etc.

- Copying information or results from one person to another.

- Work that continues even though instant serial communication would already be pursuing a different path. (For example, engineering working on something that marketing has decided should be among the last things done, if this decision has just been made: the 5 people take some delay communication it)

In other words, the single-person doing 120 hours might be something like a single-core processor at 3 GHz versus the 5-member team being a 4-core processor at 666 MHz. The former can potentially do a LOT more, for some types of workflows. This might further compensate for the precipitious drop in productivity.

So, the question remains. If normally the 5-member team is putting in 200 hours, can a single person pulling in 120 hours do the work of all of them for a few weeks before burning out? Even if we assume an incredible loss of productivity at the margin of that many hours? --91.120.48.242 (talk) 15:49, 11 March 2013 (UTC)

It seems plausible to me that it could be possible (perhaps not with the exact figures, but the general idea is correct). This is actually related to the question of why all animals need to sleep. Of course, one can consider this from biochemistry, but it can be argued that this was always the inevitable outcome of evolution. If you have two systems that have equal performance, and they both have uniform performance as a function of time, then you can take one system, cut down on its internal maintainance to let it temporarily outperform the other system and then have a period of lower activity so that it can do more internal maintainance. In the context of biology, this typically leads to a better performance (e.g. if you can run faster, you are much more likely to catch more prey). Count Iblis (talk) 16:13, 11 March 2013 (UTC)

There are several fundamental problems that I can see with this:

• You're assuming that this one person is some kind of super-human who possesses the skills and knowledge needed to do all 5 jobs. Engineering requires a set of skills and abilities that someone who is an expert salesperson does not have...and vice versa. Those 5 people may have overlapping skill sets - but finding one person who knows enough to do all 5 jobs seems really unlikely.
• When you suggest that someone might be able to do a second task while waiting for an email response or something - thereby getting more work done by 'interleaving' task, you're assuming that the original employee wasn't simultaneously working 20 streams of email, responding to one while waiting on the others. Your 5 separate employees might already be 100% busy (or at least a lot more than 20% busy) just doing their individual jobs.
• Humans are not very good at multitasking. Our article Human multitasking cites multiple studies showing that people are actually very bad at multitasking - no matter what they may claim. It's interesting to note that they discuss the 'cost' of 'context switching' - the time it takes your brain to switch between tasks - which is strongly analogous to computer operating systems that multitask. The "context switch time" is something that's critical to the efficient operation of multitasking computers - so computers have hardware and software that's specifically designed to make that more efficient. Humans (especially males) seem not to have much in the way of specialization to make that work well.

So I very much doubt that one person could adequately do the work of five - even for very short periods of time...not effectively. But (of course) it depends on your definitions of "adequate" and "effective" - and on how busy those five people were in the first place. SteveBaker (talk) 03:21, 12 March 2013 (UTC)

However, our market economy has no problem valuing the work of one person at a rate five times higher than another person. This is not strictly equivalent to doing five times as much work. I find statistics such as revenue per employee interesting: for example, corporations who specialize in petroleum pipelines average several million dollars per employee, while grocery stores average just a few thousand dollars of revenue per employee (as shown in this 2007 survey. From a purely pragmatic point of view, the work and skill level required to operate a pipe valve might actually be easier than operating a cash-register; and yet one of these jobs produces, on average, thousands of times more value. Perhaps this is a stunning indictment of the inequity inherent in market valuation, or perhaps it is proof that supply-and-demand "works correctly" - I think the conclusion you draw is dependent on your views of economics. Nimur (talk) 15:09, 12 March 2013 (UTC)

In support of the OP's hypothesis, I offer a couple of observations from the belly of the corporate beast:

1) most employees' 40 hour week contains about 20 hours of productive work, max. Maybe more during emergency situations.

2) don't forget, the answer to the question "If 1 programmer can write a program in 1 day, how many days would it take 5 programmers?" is "5 days". Gzuckier (talk) 17:32, 12 March 2013 (UTC)

In general, Gzuckier, I tend to agree with the statement, although it is somewhat cynical; but to play devil's advocate here, you've trivially equated "productivity" with "number of programs produced..." and of course that equivalence relationship is invalid. Nimur (talk) 18:28, 12 March 2013 (UTC)

I can sympathize with the sentiment that one person is often more productive than a team, provided that one person has all of the skills needed for the job. One cost of teamwork is all the time that must be taken for each team member to communicate with all the others and reach agreements, while you also have the potential for slackers. (If one person is responsible for the job, he will be blamed if he doesn't meet the schedule, while a slacker on a team might escape blame if the other team members cover for him.)

That said, 120 hours per week is rather extreme. Figuring on 7 days of work, that's still over 17 hours a day, leaving less than 7 hours for sleep, not counting time to get to and from work, eat, etc., which will leave you seriously fatigued and unproductive. It turns out that being able to sleep in the office, have your meals and clothes brought to you, shower there, etc., can make a huge difference (Edison slept in a cot in the office). I find my practical limit is around 80-90 hours, and I try to do heavy brain work in the mornings, when I'm still fresh, and leave rote jobs for later, when I'm "on autopilot". I'm a computer programmer, so would do new coding in the mornings, and leave testing, which is mostly repetitive, for last.

Note that another hidden benefit of working long hours may be being alone in the office. I find the constant interruptions of others seriously impedes my ability to concentrate on a problem.

One last comment, there's nothing magical about 40 hours being the point where productivity starts to drop off. For some exhausting work, it might be well before that, while, for some easy work, far later. StuRat (talk) 17:49, 12 March 2013 (UTC)

Reference material for physics/chemistry of vegetables

I'm not sure if something like this exists, but I'm looking for some information on the physics, chemistry and biology of a range of vegetables. For example, what makes garlic sticky and odorous, why are avocados creamy, what is the underlying cellular structure of a pepper. Questions like that. Images of cells, molecules, etc, would be fantastic too. So... is there anything out there like this? Goodbye Galaxy (talk) 18:30, 11 March 2013 (UTC)

This is not quite what you're asking for, but it is close, and very good --"On Food and Cooking" by Harold McGee (amazon link [5]) has a lot of information on the physics and biochemistry of veggies. It is mostly focused on traits of culinary importance, and also has material on meats, eggs, etc. I highly recommend it to anyone with an interest in the combination of cooking and science. SemanticMantis (talk) 19:25, 11 March 2013 (UTC)

Alton Brown used to produce an excellent and humorous show, Good Eats, with strong emphasis on the science - physics and chemistry and everything else - of food and cooking. Nimur (talk) 21:14, 11 March 2013 (UTC)

BTW, avocados are creamy because of a high fat content. Unlike animal fats, vegetable fats are healthy, but do still have lots of calories. StuRat (talk) 22:54, 13 March 2013 (UTC)

hydraulic

Moved from the Entertainment desk.
Why must a liquid and not a gas be used as the fluid in a hydraulic machine? — Preceding unsigned comment added by 70.39.187.167 (talk) 12:42, 11 March 2013 (UTC)

In general because most liquids are virtually noncompressible. If you use a gas you'll lose a lot of energy to compressing and decompressing the gas. APL (talk) 12:47, 11 March 2013 (UTC)

Although steam engines and steam turbines still have their uses. OsmanRF34 (talk) 22:08, 11 March 2013 (UTC)

You have to use liquids in a hydraulic machine because if you used gases, it would be a pneumatic machine. Matt Deres (talk) 15:05, 11 March 2013 (UTC)

Pneumatic and hydraulic / gas and liquid. So, what would you call a machine that uses solids? ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:18, 11 March 2013 (UTC)

... A solid state device. For obvious reasons, solid state devices operate on totally different physical principles and have totally different applications, most commonly as semiconductor electronics. Nimur (talk) 21:04, 11 March 2013 (UTC)

There are certain rare situations where a "hydraulic" system with no liquids is used, with large numbers of small ball bearings used as a working fluid. The main advantages are the ability to withstand both very hot and very cold temperatures (enough to boil and freeze liquid systems), a total immunity from any sort of leaking causing contamination, and no cavitation erosion. Disadvantages include large size, having to custom make everything, not being suitable for pilot valve / piloted valve operation, and limited working pressure (too high and you shot peen the interior surfaces and dent or shatter the balls.) --Guy Macon (talk) 21:54, 11 March 2013 (UTC)

I thought such things existed, but couldn't find them with cursory searching (I did find systems for hydraulic transport of powders...) What are they called, or do you have any refs? SemanticMantis (talk) 22:36, 11 March 2013 (UTC)

I took a look too and didn't find anything. The one I saw was at a customer facility where I was doing some unrelated consulting, and I don't have permission to disclose any specific information from that job. I don't know what they called it. :( --Guy Macon (talk) 23:58, 11 March 2013 (UTC)

Wouldn't a cable-operated tube-type system be considered "solid" -- as in a bicycle brake-cable? ~:74.60.29.141 (talk) 23:08, 11 March 2013 (UTC)

BFKP

What is the meaning of BFKP, referring to a boring and milling machine such as this? bamse (talk) 22:20, 11 March 2013 (UTC)

Well, it might not meaning anything in English, but given that the website is in Polish, it could very well be an acronym for a Polish term. You may do well to find a Polish speaker and ask them, or perhaps ask on the Polish Wikipedia reference desk, which is here, presuming of course that you speak Polish. --Jayron32 22:26, 11 March 2013 (UTC)

I think it's just part of the model name, e.g. one particular model made by that manufacturer is the BFKP-110. Apparently these are CNC machines. Looie496 (talk) 22:38, 11 March 2013 (UTC)

(edit conflict) That's a CNC Horizontal Boring & Milling Machine, Model# BFKP-110. Nice tool if you can get the one with the Siemens controller. --Guy Macon (talk) 22:40, 11 March 2013 (UTC)

(ec) This is on the topic of "My BFKP". It’s about gopeds and is written in English, but it may as well be in Urdu for all the sense I can get out of it.

This suggests it’s something that happens to girls, but exactly what is not specified. This tells me it’s a sort of joint acronym for Brandon Flowers (BF) and Katie Perry (KP). Maybe that’s the girl thing. Whatever, it hasn’t been given official status at Urban Dictionary yet.

Elsewhere I see it can mean:

• Bionic Fuel Knowledge Partners
• Binary Fractional Knapsack Problem
• Barack, Ferrazzano, Kirschbaum & Perlman (who seem to have changed their name [6]). -- Jack of Oz ^[Talk] 22:51, 11 March 2013 (UTC)

Interesting, but it's still a BFKP-110 CNC Horizontal Boring and Milling Machine. --Guy Macon (talk) 00:11, 12 March 2013 (UTC)

Yes, you already told us that. But are you saying they chose those four letters at random, and they stand for nothing specific? -- Jack of Oz ^[Talk] 01:12, 12 March 2013 (UTC)

I'm fluent in Russian but not in Polish, but let me take a guess: "F" might stand for "milling" ("frezerovaniye/frezerovochny" in Russian, probably a similar word in Polish), and "KP" probably has to do with computer control ("komputerny pravleniye" or something like that). FWiW 24.23.196.85 (talk) 00:23, 12 March 2013 (UTC)

Thank you for the replies. I had guessed BF to stand for Bohren/Fräsen (German for "boring/milling") considering that the machine is from Germany (GDR in fact). bamse (talk) 23:52, 12 March 2013 (UTC)

Is the panda the only herbivorous carnivoran?

I don't have much to add beyond the title. The article Carnivora mentions the panda as among "a few primarily herbivorous species", but that's not cited. Are there in fact any others? If so, what are they? ± Lenoxus (" *** ") 23:47, 11 March 2013 (UTC)

The bearcat is another Carnivora species that's mostly vegetarian. 24.23.196.85 (talk) 00:13, 12 March 2013 (UTC)

Sloth bears, perhaps. Even pandas can eat meat. Claims that something only eats meat or only eats plant matter tend to be exaggerated. Wnt (talk) 02:02, 12 March 2013 (UTC)

Nope -- the sloth bear mostly eats insects (especially termites). 24.23.196.85 (talk) 04:27, 12 March 2013 (UTC)

According to Red panda (a species not closely related to great pandas and closer related to racoons and mustelids) it is primarily herbivorous, though like great pandas do eat some animal products like fish and eggs. --Jayron32 05:57, 12 March 2013 (UTC)

Gorillas are primarily herbivores, but sometimes they eat ants and termites. --PlanetEditor (talk) 08:13, 12 March 2013 (UTC)

• Here's the answer, if you restrict to Carnivoran species that have been documented to consume at least 95% vegetable matter, from this study, titled "Shape at the cross-roads: homoplasy and history in the evolution

of the carnivoran skull towards herbivory", available here [7].

" As a

result, five species were considered as specialized herbivores in this study: the giant panda ( A. melanoleuca , Ursidae), the red or lesser panda (A. fulgens , Ailuridae), the bushy-tailed olingo ( Bassaricyon gabbi , Procyonidae), the kinkajou ( Potos flavus , Procyonidae) and the specta- cled bear ( Tremarctos ornatus

, Ursida "

-- So, there are five primarily herbivorous carnivorans, and we had the two pandas picked out. (Also note that the Gorilla mentioned above is largely herbivorous, but not a Carnivoran.) SemanticMantis (talk) 15:07, 12 March 2013 (UTC)

SemanticMantis, gorillas sometimes eat ants and termites, this make them occasional insectivores. And insectivory is a type of carnivory. --PlanetEditor (talk) 15:26, 12 March 2013 (UTC)

Thanks Planet editor. But in this case, Carnivoran does not mean "is a carnivore" (as we've illustrated with the pandas et al.) What it means is "a species in the Order_(biology) named Carnivora". So not all carnivores are Carnivorans, and not all Carnivorans are carnivores. This is an unfortunate turn of language, but there it is. Using standard definitions, Gorillas are neither Carnivoran nor carnivores. SemanticMantis (talk) 15:57, 12 March 2013 (UTC)

Hmm, thanks for the clarification. --PlanetEditor (talk) 16:05, 12 March 2013 (UTC)