Wikipedia:Reference desk/Archives/Science/2018 April 22

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April 22

Detecting bird "pregnancy"

Recently I was talking to someone who was feeding gulls, and he pointed out a gull which he claimed was a "pregnant" female, i.e. one that would be laying eggs soon, because it was slightly fatter than the other gulls. (I suggested the neologism "eggnant".) Is it actually possible to tell by looking at a female bird if she's "eggnant," as with pregnant mammals? 169.228.151.215 (talk) 03:27, 22 April 2018 (UTC)

Sometimes. --jpgordon^{𝄢𝄆 𝄐𝄇} 04:31, 22 April 2018 (UTC)

Interesting. The gull I mentioned didn't appear to have a bulge on its abdomen, though, it just looked wider across the torso than most. 169.228.151.215 (talk) 04:52, 22 April 2018 (UTC)

Hens become "eggbound" when they've a bun in the oven too long. They don't look so well but don't look fatter. Gulls are probably similar. InedibleHulk (talk) 06:01, 22 April 2018 (UTC)

Just to note, "probably similar" there is a link to egg binding (unpiped to help readers realize WHAAOE). DMacks (talk) 20:34, 22 April 2018 (UTC)

They are. InedibleHulk (talk) 06:07, 22 April 2018 (UTC)

The word you're looking for is "gravid". Abductive (reasoning) 06:14, 22 April 2018 (UTC)

TIL gravid means "carrying eggs" as well as "pregnant". Thanks, Abductive! -Nunh-huh 04:52, 25 April 2018 (UTC)

What ever became of the user named something like Kurt Shaped Box who lived for questions like this?73.211.241.4 (talk) 02:31, 23 April 2018 (UTC)

User:Kurt Shaped Box silently stopped contributing in September 2016. DMacks (talk) 02:54, 23 April 2018 (UTC)

Shark bite

Can a shark bite through a knight's armor? 2601:646:8E01:7E0B:0:0:0:9A39 (talk) 06:23, 22 April 2018 (UTC)

That would depend on the shark, and the armor. According to Shark suit, chainmail seems to be preferred, and that was something that knights wore. ←Baseball Bugs ^{What's up, Doc?} carrots→ 08:11, 22 April 2018 (UTC)

Sharks are known for their numerous teeth and their powerful shearing effect. But what's the simple bite force like, compared to a large feline or hyena? - animals which are known particularly for their crushing ability, rather than sharpness. Andy Dingley (talk) 08:41, 22 April 2018 (UTC)

"A 2008 computer model estimated that a 21-foot (6.5-meter) great white shark would produce nearly 4,000 psi (17,790 newtons) of bite force, that figure hasn't been directly measured". [1]

Tests by Robert Hardy using a 710 Newton English longbow found that it could penetrate medieval armour at very close range; see English longbow#Armour penetration.

So the answer seems to be "yes", Alansplodge (talk) 12:12, 22 April 2018 (UTC)

Yes, but this is just a computer model, and this is the peak force at the back of the bite. Add to this that sharks would not apply all their force to all bites.

In reality sharks sharks have saw-like teeth and they shake the prey once bitten to cause a sawing effect. It's about the sharpness more than about the force. --Hofhof (talk) 13:01, 22 April 2018 (UTC)

• Further, I would have to consider the source Alan cites as unreliable, if it can't even get the units right. The PSI is a pressure unit—pounds per square inch, where "pound" means pound force— but the newton is a force unit. 17,790 newtons is 4,000 pounds force, not psi. Or if it meant to talk about pressures, 4,000 psi is 27.6 megapascals, i.e. meganewtons per square meter. --69.159.62.113 (talk) 21:17, 22 April 2018 (UTC)

• The original Journal of Zoology paper seems to be here [2]. It uses Newton except in the abstract. The relevant part seems to be "Assuming isometry, scaling the 35° gape angle data for a 6.4 m, 3324 kg white shark yields maximum anterior and posterior bite forces of 9320 and 18 216 N". While doubts over pop science reports are quite resonable, it's often helpful to at least check out where this claim is likely coming from, particularly if it's peer reviewed. Nil Einne (talk) 07:15, 23 April 2018 (UTC)

• BTW, the PLOS One paper mentioned in the National Geographic source is here [3] and well it's PLOS One so open access. It uses MPa with a psi conversion for the pressures and Newton with a lbs (appears to accurately be pound force) for the forces. The relevant parts seem to be "taxon representative molariform bite forces ranging from 900 to 8,983 N (202 to 2,019 lbs)" and "taxon representative caniniform tooth-pressure values ranged from 195 to 1,344 MPa (28,282 to 194,931 psi)" and "Taxon representative molariform tooth-pressure values ranged from 203 to 1,388 MPa (29,443 to 201,312 psi)". As sort of mentioned in the National Geographic source, the bite forces were measured. (The bite pressures were inferred.) Yes, these are crocodiles, but there's another model mentioned in the Zoology paper "applying a similar FE methodology, computation of the maximal anterior bite force in a 267 kg African lion yields a figure of c. 3300N". I mention these because if Alansplodge suggestion that 710 Newton is enough to penetrate armour, from a pure force standpoint, it doesn't even seem to be even close to being in doubt unless shark (and maybe lion) bite forces are very unusual so the models are way, way, way, way off. I make no comment on other factors. Nil Einne (talk) 07:36, 23 April 2018 (UTC)

• Oh I also came across [4], it seems at least one company does make wetsuits from either stainless steel or titanium mesh [5]. I don't know how these compare to older armour, they're likely designed much more for flexibility and lightness but also likely have a fair amount more tech. According to the first source, the founder doesn't recommend them for great white shark bites although as noted, even without the armour being penetrated there is still risk of significant injury. Another thing mentioned, also in some non RS discussions I came across, is the fact it can doesn't mean it will. Sharks have a tendency to let go if they come across something hard. Nil Einne (talk) 07:55, 23 April 2018 (UTC)

• This video, while not even close to being an RS [6] also mentions the likely ineffectiveness of chainmail wetsuits against a dedicated great white shark. This on cage divers mentions the general reluctance of sharks to bite cages since they don't look like food although I'm not sure how much this applies to a human in armour. (But my understanding is generally humans aren't interesting to sharks, and I wouldn't be surprised if sharks are even less interested in humans in chain mail.) Of course being rare doesn't preclude it happening if you try hard enough, as the few shark attacks and incidents like these [7] [8] show, crap can happen. Nil Einne (talk) 09:09, 23 April 2018 (UTC)

As some have noted, you don't necessarily have to penetrate armor to harm whatever's inside. Humans are squishy bags of mostly water. If you get hit, the energy still has to go somewhere. Armor simply distributes the force throughout the body, which protects against sharp object penetration but doesn't prevent blunt force injury. This is why blunt weapons like maces were useful, to attack armored combatants by causing blunt trauma. --47.146.63.87 (talk) 09:31, 23 April 2018 (UTC)

Tsar Bomba's effect on the Earth's Position in space

I was wondering about the effect that a massive explosion like the Tsar Bomba would have on the earth's position in space. I did some back of the envelope calculations as follows: we know that the total yield of Tsar Bomba was 50MT. That's about 210PJ. Most of that energy would have gone into heating the atmosphere, deforming/destroying all sorts of things, creating its crater, etc. But some of the energy would have been a force against the earth's surface. The bomb produced a shock wave which propagated omnidirectionally. Some of it propagated down to the earth's surface (where it in fact, reflected off it). Some of it also propagated upwards. Upon reaching the top of the atmosphere, it would be expected to blow some of the air molecules off into space. It also radiated a large amount of particles upward into space. This mass being displaced away from the earth should have imparted an acceleration on the earth. Even if the mass push upwards was slower than the escape velocity of earth and was simply forced into orbit, the earth would still experience acceleration, and the mass would likely never return to earth as it would be blown off by solar wind. In addition, the large flux of particle and electromagnetic radiation that went downwards towards the earth should have imparted a radiation pressure upon the earth.

I guessed that the yield energy converted into a net kinetic energy change of the earth would be say 10%. I don't really know if 10% is fair or not. I suspect it's possible that almost all of the energy going into motion of the constituent parts of the earth's structure would have been fully dissipated in the deformation of the same, making this an entirely inelastic process. In any case, the 10% figure gives 21PJ. Given that the earth is 5.972e24kg, we therefore have a change in the earth's velocity of 8.39e-5m/s. That's a tiny change, but since 1782259200 seconds have expired since the detonation, we'd expect by now that the earth is around 150km away from where it would otherwise have been. By the year 3061, we'd expect the earth to be shifted by 3000km, and after 1,000,000 years the shift would be 3,000,000km. But when I looked for confirmation of my reasoning I found these links [9] and [10]. They both seem to think that ejection of mass was zero (which I think is a totally incorrect assumption) and therefore conclude that no acceleration was imparted (also incorrect since it ignores the radiation pressure). 103.228.155.110 (talk) 09:52, 22 April 2018 (UTC)

Your reasoning is incorrect, conservation of momentum needs to be taken into consideration when considering where the energy is directed. The amount of mass ejected into outer space, free from Earth's gravitational pull, is all but negligible, so in fact the vast majority (far greater than 90%) of the blast energy is directed at the air above, rather than the earth. Also, there is a substantial deceleration from the initial detonation velocity by the time any air gets ejected from the atmosphere so the impulse imparted to the earth is basically nothing. Radiation pressure also cannot be thought as acting only on the earth; all forces come in pairs per Newton's third law.--Jasper Deng (talk) 10:59, 22 April 2018 (UTC)

Imaging the all energy of E=2.1×10¹⁷ went into accelerating some mass $m=2E/v_{2}^{2}$ to the escape velocity of $v_{2}=11.2$ km/s. Then the kinetic energy of Earth would have changed by $\Delta E=(mv_{2})^{2}/(2M)=2(E/v_{2})^{2}/M$, where M is the mass of Earth. The result is $E\approx 27$ J. The change of the Earth's velocity would have been $E\approx 3\times 10^{-12}$ m/s – a negligible value. Ruslik_Zero 17:51, 22 April 2018 (UTC)

• It's better to treat the earth as a closed system. The explosion cannot affect the center of mass of the system unless it causes mass to leave the system. Blasting mass into orbit does not do this. The only mass that the explosion pushes out of the system is a mass of any photons that leave the system, and this is inconsequential: it's tiny by comparison to the reflected sunlight. There are several even smaller effects: mass thrown into orbit will increase the system's capture of solar photons and solar wind This is tiny compared to changes caused by the atmosphere expanding due to anthropogenic warming. Yet another tiny effect: if the explosion temporarily affects the earth's albedo, the sun's photon pressure changes as more (or less) photons are reflected back into space. This is is even smaller than the effects on albedo caused by weather, fires, volcanos, agriculture, contrails, etc. -Arch dude (talk) 04:02, 23 April 2018 (UTC)

Note that large releases of energy, like earthquakes, can alter the Earth's rate of rotation, by moving material around and thereby changing its moment of inertia, but yes, this isn't the same thing as its orbital position. Earth is a big old ball of rock and metal. It takes a lot to move it. --47.146.63.87 (talk) 09:18, 23 April 2018 (UTC)

Bass cabinet

How do gallien kreuger get such good bass response from rhier small cabinets?86.8.201.80 (talk) 13:31, 22 April 2018 (UTC)

See Gallien-Krueger for our article. I'm sure that the marketing literature available from their website will address the issue, if not in an entirely unbiased manner. Tevildo (talk) 15:52, 22 April 2018 (UTC)

I have looked at the website and they do not say how they achieve the low frequency response. That's why I'm asking here.86.8.201.80 (talk) 17:00, 22 April 2018 (UTC)

Well, for example, on the website we have "[The enclosures] utilize special bracing to eliminate standing waves while providing rock solid structural support to reduce cabinet resonance ... tuned ports, GK’s innovative Horn Bi-Amp System, passive crossover with attenuator for full-range operation ... [the] enclosures are equipped with proprietary neodymium drivers...". Any more detailed information will be proprietary to GK, and not available publicly. See trade secret. Tevildo (talk)

The Wikipedia articles Loudspeaker enclosure and Guitar speaker cover construction techniques that have not changed over many years. DroneB (talk) 10:34, 23 April 2018 (UTC)

What is the exact reason that woman can't get pregnant while breastfeeding?

What is the exact reason that woman can't get pregnant while breastfeeding? Maybe you can refer me to the relevant article here on Wikipedia and I'll read it.93.126.116.89 (talk) 23:10, 22 April 2018 (UTC)

Breastfeeding#Mother. Ian.thomson (talk) 23:13, 22 April 2018 (UTC)

Lactational amenorrhea. Carbon Caryatid (talk) 23:16, 22 April 2018 (UTC)

The second article (also linked in the first) is an important read. It's definitely not impossible for pregnancy to occur despite breastfeeding. Nil Einne (talk) 09:12, 23 April 2018 (UTC)

The baby wakes up, starts crying, bites her nipple and the woman is definitely no longer in the mood. Besides, the position is going to be pretty awkward, no matter how you do it, especially if there is no baby involved. (Unless of course it is one of the women who is doing the breastfeeding.) Real life is not a weird kinky porn movie. :-)John Z (talk) 00:12, 28 April 2018 (UTC)

Women definitely CAN get pregnant whilst breastfeeding! The article on lactational amenorrhoea referenced above will tell you more.RichYPE (talk) 14:12, 28 April 2018 (UTC)