Wikipedia:Reference desk/Archives/Science/2017 March 31

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March 31

Question about the physics

Question #1: How much force is required to move a mass of 1kg from rest with a constant speed of 1 m/sec in space? Question #2: Let we have mass m of 1 Kg at rest on which a force of 1 N is applied in space

Case #1: A mass attains its final velocity when a 1N is removed after 5 seconds.

Case #2: A mass attains its final velocity when a 1N is removed after 20 seconds.

This means the final velocity of a mass of 1Kg in case #2 is greater than case #1. Although 1N force is involved in both cases but a greater force (also >1N) is required in opposite direction in order to stop the motion of mass of 1kg in case #2 say after 30 sec– why?

Does this mean force is accrued potentially in an object due to its constant application if the object is in acceleration mode which can be determined from its impact as in above example?2001:56A:7399:1200:7C13:D130:E1D7:434A (talk) 00:18, 31 March 2017 (UTC)EEK

Force is not accrued, it is applied. Since F = m*a, and a = Δv/t, then case 2 has accelerated for 4 times as long, so if they both started at rest, case #2 is moving with 4x the velocity of case #1. If you want to decelerate the object with a same force in the opposite direction, you'd have to apply it for the same amount of time (20 seconds). If the deceleration occured over a shorter time span, it would apply a commensurate amount of increased force. This is easier to understand if you think about it as a conservation of momentum problem rather than a force and time problem. Just do the dimensional analysis. --Jayron32 00:22, 31 March 2017 (UTC)

i was just thinking that force ceases its strength when used its effort in increasing the velocity at any given instant which means an incremental increase in applied force (effort), is required for the gradual increase in momentum / instantaneously velocity of an object an thanks for your answer. — Preceding unsigned comment added by 2001:56A:7399:1200:3078:21D0:B447:EDC6 (talk) 04:32, 31 March 2017 (UTC)

Newton's laws of motion are essential reading here. The first law tells you that NO force is needed to KEEP a mass at a constant speed in space. The second law underlies the definition of one N (Newton) as the force that can accelerate or decelerate one kilogram of mass at the rate of one metre per second squared. The mass accelerates or decelerates exactly as long as a force is applied. So in the OP's Case #2 the mass reaches 4 times higher final velocity than Case #1. It then continues "forever" at that final velocity (First Law again). You can decelerate it as whatever finite rate you choose. If the braking force is also 1 N then the deceleration to zero speed will take the same time as the acceleration took. Blooteuth (talk) 17:19, 31 March 2017 (UTC)

thanks for your answer but i meant a sudden stoppage at 30th sec in both cases

It is impossible to bring the mass to rest in zero distance, but hitting a concrete wall or a large tree can bring something to rest in a very short distance with very large forces that usually cause damage. In the second example, the mass will have accrued four times the momentum and sixteen times the energy, so will be correspondingly more difficult to stop. Dbfirs 05:57, 1 April 2017 (UTC)

I said "You can decelerate it at whatever finite rate you choose." Do you realize that "sudden stoppage" would require an impractical infinite deceleration? Consider why cars need a Crumple zone to avoid this! Blooteuth (talk) 13:30, 1 April 2017 (UTC)

The basic purpose of my question was that push or pull is required to make things move with speed /velocity or its higher derivatives - not just simply changes their speed in space. We know F=ma but there is no direct relationship of Force with Velocity / Speed. I may be wrong but the potential (unbalanced) force carried by the object moving with constant speed in space can be measured if used newton’s strong stationary spring. — Preceding unsigned comment added by 2001:56A:7399:1200:4879:BD23:7320:19C (talk) 02:43, 4 April 2017 (UTC)

Are people with anencephaly conscious?

I've done some googling and can't find anything. I remember watching a video of Giulio Tononi where he said if u remove the cerebellum the person is still consciousness, but removing the cerebrum the person is dead. This makes common sense. So are people with anencephaly just a piece of meat? Money is tight (talk) 05:18, 31 March 2017 (UTC)

The article on Anencephaly states "anencephalic infants are not aggressively resuscitated because there is no chance of the infant's ever achieving a conscious existence." Wymspen (talk) 10:44, 31 March 2017 (UTC)

Anencephaly literally means 'no brain'. Ruslik_Zero 12:21, 31 March 2017 (UTC)

In reality they have some brain, but major parts are missing. --Dikipewia (talk) 16:59, 1 April 2017 (UTC)

The presence of a brain stem makes this a hard one to answer. You cannot say that no neurons, or even no CNS neurons, are active. Enough like consciousness happens in the brain stem that I wouldn't say it is even implausible. And even foci of intact cerebral cortex can exist. [1] It's just... a hopeless situation. Any of us can get to the point where we're more eager to catch Charon's water taxi than to keep dog-paddling in the shallows. Wnt (talk) 23:21, 2 April 2017 (UTC)

Crickets in March/April, then not again till July

I live in northeast Illinois. I often hear crickets in March and April, but then I would not often hear them again until July. So there's a two-month gap. The crickets I hear in early spring is lower pitched than what I hear during the summer and doesn't make quite a chirping sound, but an upward pitch in each sound it makes. During the two-month gap, I can hear them after it rains, which the sounds is somewhat constant. So what's the reason why crickets sound different in early spring than summer and why usually no cricket sounds for two months? PlanetStar 07:03, 31 March 2017 (UTC)

You might be dealing with two different species. Many locusts (similar to crickets) employ a swarming strategy of all coming out of the ground at once, and overwhelming predators, then reproducing and laying eggs and dying off quickly before predators eat them all. Perhaps your crickets do the same thing. StuRat (talk) 07:06, 31 March 2017 (UTC)

Why do some lone geese without offspring hiss at a man yet others in a group flee from a lone 7th grader?

Is it just individual aggressiveness differences? Also, I once saw a guarded goose nest of eggs no more than a few feet from a road when there was plenty of less unsecluded grass right there (albeit still easily visible from the road). Why'd it do that? Sagittarian Milky Way (talk) 09:20, 31 March 2017 (UTC)

By the same reason why some lone dogs (especially small ones) will bark at you furiously but other in a group flee from a lone 7th grader. Ruslik_Zero 12:19, 31 March 2017 (UTC)

A gander has the job, during the nesting season (late February to mid-May), of defending the female, the nesting territory and the eggs, and will chase any intruder. Ways of dealing with an aggressive goose include grabbing it to show who is boss, employing it as a house guard or stuffing it for dinner. Blooteuth (talk) 16:40, 31 March 2017 (UTC)

Geese are generally gregarious animals. Gregarious animals often behave very differently when they are alone. The lone goose was possibly responding to the approach by hissing because the individual goose was the only potential target. However, by doing this, it was taking a risky strategy. When in a group, they run away because there are more of them as potential targets and it is a less risky strategy. DrChrissy ^(talk) 21:51, 31 March 2017 (UTC)

Why should animals not develope some individual character. Science has already proven very impressivly that animal intelligence was and mostly still is very underestimated. Likewise you can assume the same for a general ability to develope surprisingly different individual character. --Kharon (talk) 22:23, 31 March 2017 (UTC)

Please do not misunderstand me. I was talking about general behaviour because we have no data on the individual geese. I would be one of the first on here to argue that many animals CAN and do develop individual characters. If you want to read more about this, I suggest Personality in animals which I have edited quite a bit. DrChrissy ^(talk) 23:01, 31 March 2017 (UTC)

Being close to the road could have benefits, like being able to see predators (dogs, foxes, etc.) approaching. If we are talking about a Canada Goose, they can put up a reasonable defense against such animals, as long as they see the threat coming. More skittish predators might also be scared off by cars. Canada Geese seem quite willing to live next to traffic. As for hissing at a man, he probably got too close to the nest. StuRat (talk) 22:16, 31 March 2017 (UTC)

Identification of animals in 18th century book

A question at WP:RDH here eventually led to me producing Charles Catton's 1788 book at wikisource:Animals drawn from Nature and engraved in aqua-tinta. I have speculated at its talk page what the various animals might be. Catton had a fairly strong concept of "species" and would distinguish the particular species he illustrated from the generality of animals of that sort. I haven't been able to reference my original research because I have not found anything appropriate. Does anyone know of a reference for better-informed identifications than mine? The "Animal of the Weasel kind"[2] is of particular interest to me. Catton had been told it was a "striped polecat". Its body was 12" long and the tail 10"; it had 5 claws on the front feet and four on the hind. It came from Bengal (though I suspect the origins he had been told of were sometimes unreliable). Can anyone suggest an identification (and for any of the other animals)? Thincat (talk) 09:43, 31 March 2017 (UTC)

My first thoughts for an "animal of the weasel kind" from Bengal were for some kind of mongoose, but the stripey ones, Narrow-striped mongoose and Grandidier's mongoose are Malagasy rather than Bengali. There is a striped polecat which looks very like the picture, that is African. It's not unreasonable to suspect that someone in Bengal ion the 18th Century could have a pet which had been picked up by a ship on its way round the Cape of Good Hope. DuncanHill (talk) 11:41, 31 March 2017 (UTC)

It looks very much like a species of skunk, many of which are similar (to be almost indistinguishable from) some species of true polecats. The Mustelids are the largest carnivorous family in the world, and there are several that look very much like those pictures. Skunks are of the family Mephitidae and are often grouped into a superfamily Musteloidea which includes weasels and polecats as well as racoons and the like. --Jayron32 11:54, 31 March 2017 (UTC)

I doubt a lady would keep a skunk in her muff. DuncanHill (talk) 12:10, 31 March 2017 (UTC)

Skunks as pets would disagree with you. --Jayron32 12:26, 31 March 2017 (UTC)

@DuncanHill: No, a lady would never do that. I suppose that is why Catton thought it wasn't an "offspring of a miscellaneous copulation."[3] Thincat (talk) 08:31, 2 April 2017 (UTC)

• Others from that book (which may or may not match the names he gives) are the coati (which he calls "coti") the Tahitian dog he calls the "Otaheite dog" (otaheite is an alternate demonym for Tahiti.), the Lion tamarin is the "lion monkey", I believe he confuses a Baboon with a Mandrill, and the animal he calls a "Child of the Sun" is really the true Baboon. The Ring-tailed lemur is what he calls a "maucauco", the glutton is today called a wolverine. The rest of the animals seem to match their accepted English name. --Jayron32 12:09, 31 March 2017 (UTC)

Thank you for your replies. It hadn't occurred to me that the "Animal of the Weasel kind"[4] might be a skunk. Skunks come from the Americas (mostly, but see Mydaus) whereas Catton had been told his came from Bengal. I'll look into all that. Catton was told his "Child of the Sun"[5] came from South America but if it is what we now describe as a baboon (which I think it is) then he must have been misinformed. Catton himself regards it as a type of baboon. Since asking my question I have found an 1825 book saying that Catton's "Yellow bear"[6] is also called a "Cinnamon Bear", classifying it as Ursus americanus (and was kept at the Tower of London menagerie).[7] We now have Ursus americanus cinnamomum, Audubon and Bachman, 1854. Thincat (talk) 08:08, 2 April 2017 (UTC)

The author says it's a "striped pole-cat" and we have an article Striped polecat. I'm not inclined to deep thinking here. That weasel family member looks like it has two stripes, as in the picture - but it has a browner coloration than the diagram, and it lives in Africa, not Bengal. But there might be some variation in color, and "brought from Bengal" doesn't guarantee it wasn't brought as an exotic from some other country. Here's a photo with the right background color: [8] (zorilla is another name, according to our article) Wnt (talk) 23:27, 2 April 2017 (UTC)

Feynman Lectures. Lecture 51. Ch.51-2 Shock waves [9]

...

Figure 51–3

— Feynman • Leighton • Sands, The Feynman Lectures on Physics, Volume I

Suggest please, what does Feynman mean by "Wavefront" in figure 51-3? Is it a half of the visible cone wave shown in Figure 51–2? Username160611000000 (talk) 13:51, 31 March 2017 (UTC)

The wavefront is a connected set of points where the phase of the wave function is the same specific, arbitrarily-specified value. Nimur (talk) 14:09, 31 March 2017 (UTC)

In Lecture 47 [10] Feynman says that the pressure (or displacement, or density ) can be the wave value φ(x,t). So I understand Figure 51–2 such that the visible cone have equal pressure value and the visible cone is the wavefront. But then I don't understand the Figure 51–3 because at the apex pressure must be the same as at other points of wavefront (or at least not very different), but according fig. 51-3 we see zero pressure at the apex. Username160611000000 (talk) 15:19, 31 March 2017 (UTC)

I read the vertical axis in 51-3 as mislabelled "Pressure", I think it should be Distance, orthogonal to the horizontal axis. Zero pressure makes no sense. Blooteuth (talk) 16:14, 31 March 2017 (UTC)

Well, I think the vertical axis can have a value 100000 Pa at lowest point of the curve and 100001 Pa at highest point of the curve. Also I noticed little arrow with c_w which means phase velocity, but it's strange that the arrow is directed only rightwards and not upwards. Username160611000000 (talk) 17:53, 31 March 2017 (UTC)

The curves in Fig. 51-3 are conceptual cross-section sketches of the upper half of the wave cone photographed in Fig. 51-2. Markers c and b correspond to tangential points on the circular wavefronts centered on x₁ and x₂ respectively. I don't find the third sketch for t₃ > t₂ in which marker a is imminently overtaken by b helpful to consideration of a projectile moving at constant supersonic speed because the sketches don't delineate the projectile itself, and the uninterrupted distance axis suggests it is decelerating to sonic speed. The accompanying text jumps from explaining the slight non-linearity of the conical projectile shock wave to considering the spherical shock waves (light and sound) from a bomb explosion. Blooteuth (talk) 15:10, 31 March 2017 (UTC)

• I think I have understood. Figure 51–3 shows something like Fig. 47–2. Username160611000000 (talk) 19:43, 31 March 2017 (UTC)

Air safety

I'm about three miles northwest of London City Airport. At 3 o'clock British Summer Time looking east I saw at an elevation of thirty degrees an aircraft flying south. A small plane (descending) beetled past heading north about half an inch below it. How close together were those aircraft in reality? 79.79.142.236 (talk) 14:49, 31 March 2017 (UTC)

• What does "about half an inch below it" mean? Depending on the answer, the distance you seek could be anywhere between "about half an inch" and six miles.

Also, trigonometry is nice, but using sites such as this is smarter (with some luck you could identify the aircraft routes). Tigraan^{Click here to contact me} 15:06, 31 March 2017 (UTC)

Many complicated rules dictate the minimum separation of air traffic. In some circumstances, strict rules require the aircraft to be thousands of feet apart (or some other specified value in meters/miles/nautical-miles). In other circumstances, as long as the planes don't touch and the pilots can take responsibility for ensuring safe operation, the planes can get really close together.

Most commercial air traffic rules in most parts of the world govern something like a thousand feet of vertical separation and two miles of horizontal separation front-to-back, and maybe a mile of separation side-to-side. Whether those minima even apply depends on where each airplane is in three dimensional space, and what weather, airspace, and traffic exists near them and near the controller (if there is a controller); and what type of operation the aircraft is conducting. For example, civil air transportation (passenger-carrying) flights usually enforce stricter guidelines than other types of operations, like freight, military, or "other" flights. The reality is, we can't easily summarize all the rules: you can start by picking up a copy of, say, the FAR/AIM (which applies in the United States) or browsing through, e.g., ICAO/EUROCONTROL guidelines for RADAR separation. It might take a few hundred hours to go over all the applicable rules for all the possible scenarios, which is why the job requires so much training. (...did you know that air traffic controllers in the United States can log the number of hours they spend studying? 14 CFR 65.20, 65.35, and basically all of 65 Subpart A and B ...) Nimur (talk) 15:50, 31 March 2017 (UTC)

Tigraan's link to FlightRadar24 is a wonderful site but it cannot show small propeller planes without transponders.

I don't know how close in space the planes came but NATS (National Air Traffic Services) the UK's largest air navigation service provider should know everything that happens within a radius of 2 nm and up to 2,500 feet in which radar control and IFR (Instrument Flight Rules) apply. The London City Airport logo slogan "Get closer." is not an unqualified permission to pilots. The airport has only a single steep ILS glideslope to its 1,508 m (4,948 ft) long runway that requires flight traffic to queue orderly, and single-engine or single-pilot flights are not permitted. Blooteuth (talk) 16:07, 31 March 2017 (UTC)

Distances and speeds in 3 dimensions can be distorted to a viewer by parallax issues. --Jayron32 16:53, 31 March 2017 (UTC)

You appear to be assuming that one must have been directly above the other. However, planes are also separated horizontally: from your viewpoint they may have appeared very close, but the "small" plane may actually have been both larger than it seemed, and a lot further aweay from you. Wymspen (talk) 18:07, 31 March 2017 (UTC)

How does my body maintain constant temperature?

Where does the heat energy come from? If the external temperature is at 37 degrees Celsius, then will I just let the environment regulate my body temperature? 140.254.70.33 (talk) 18:17, 31 March 2017 (UTC)

The Wikipedia article Thermoregulation covers this topic. You'll find many answers there. If the external temperature is 37 °C, your body will still generate heat through its normal metabolism processes and your body will have to take active measures to keep you from getting too hot, such as by sweating. Deli nk (talk) 18:23, 31 March 2017 (UTC)

So, there is no way to shut down the "normal metabolism processes" until the temperature lowers? I wish I were a thermoconforming organism. 140.254.70.33 (talk) 18:33, 31 March 2017 (UTC)

You can consciously increase your metabolic rate, I'm not sure if there are ways to decrease it. Wim Hof has demonstrated how you can do this, see e.g. here and here. It's not something that only he can do, he gives courses allowing everyone to do this, although you may not become as good as Wim Hof is at this. The core idea is simple, you just do hyperventilation exercises, the body doesn't like the changes in blood acidity due to hyperventilation, what happens over time as you keep on doing hyperventilation exercises is that you train the body to increase the metabolic rate and thereby use more oxygen (way beyond what happens normally when you do this). This then allows you to stay out in ice cold conditions with poor clothing for a long time. Such methods have actually been used for many thousands of years by Tibetan Buddhist Monks. As part of their cold endurance training they'll wear wet clothing and sit outside in ice cold windy conditions for many hours while hyperventilating. When you have exercised this enough, entering cold conditions automatically leads to faster breathing, there is then no hyperventilation anymore and you don't have to consciously control the breathing anymore. It's similar to how you automatically start to breath faster if you start to run. Count Iblis (talk) 19:35, 31 March 2017 (UTC)

Wikipedia has an article on this here. --Jayron32 20:05, 31 March 2017 (UTC)

Lol Jayron. This must be true! Reptiles definately know how to regulate their body temperature.

Jocking aside there seem to be no reliable ways or "modern" technologies to change it exept brute force because even in the most advanced medical treatments, where a pacient has to be cooled down, like for example organ transplantations, the pacients are cooled very simply brute force with ice water. --Kharon (talk) 22:08, 31 March 2017 (UTC)

Independent of Wim Hof methods (that seem almost as successful as those of inedia practitioners), acclimatization is a real thing. Hofhof (talk) 10:10, 1 April 2017 (UTC)

Even if the above is as good as it sounds, which I doubt, it comes dangerously close to medical advice that should not be given here. Tigraan^{Click here to contact me} 12:21, 1 April 2017 (UTC)

There are medical procedures where they lower the body temp to slow damage from oxygen depletion. These typically involve stopping the heart. As for minimizing the body's need to heat or cool the body under normal conditions, just keep the ambient temp, humidity, and wind speed comfortable. StuRat (talk) 22:22, 31 March 2017 (UTC)

Think Stu is referring to the use of Chlorpromazine. Must be over 40 years ago that a Jewish doctor told me about how the Nazis often fished downed aircrew out of the sea alive, only to have them die shortly after -from hypothermia. By chance, they observed that when an concentration camp inmate was treated with this insecticide (which was its only known use back then), they where less bothered by the cold. So they immersed camp inmates in ice cold water and experimented. After the war, a French company promoted this drug (under their own brand name) for hypothermic surgery. They could not mention how they they had become aware of this, because Nazis science was abhorrent and no-no. (but a lot of French doctors went to work in Germany as they got paid well) . It later got used as a psychiatric drug. Should anyone here be familiar with patients under going treatment with Chlorpromazine they will back me up, that they often wear light clothing in cold conditions and not yet not appear to notice the cold. Very handy for open heart surgery where they have to cool the body down.--Aspro (talk) 18:31, 1 April 2017 (UTC)

Wim Hof has scientifically falsified the widely held belief that we don't have conscious control over thermoregulation. It has also been verified that people can gain this ability by following training, allowing them to easily tolerate cold conditions that would normally be considered to be lethal. So, this cannot be dismissed as some genetic fluke. While one has to be skeptical when people make bold claims that go against conventional scientifically established facts, in this particular case the official scientific point of view was never well established (if you try to find what it is based on you end up with arguments from authority) while there exists a large number of counterexamples, not just from Wim Hof, but there are a large of people who are able to do such things as swim in arctic waters without suffering hypothermia. Count Iblis (talk) 22:34, 31 March 2017 (UTC)

Even 5 year old's can swim in the Arctic Ocean and I don't think she had any special training. CambridgeBayWeather, Uqaqtuq (talk), Sunasuttuq 07:47, 1 April 2017 (UTC)

Brrr! I wouldn't recommend it. I have a brother and his wife who go swimming every day of the year in the Atlantic and you can feel the cold radiating off them when they come out! (Yeah I know cold doesn't radiate but that's what it feels like). Dmcq (talk) 11:03, 1 April 2017 (UTC)

Dying or surviving in cold water depends on some factors besides your "consicous control over thermoregulation." A heart attack is certainly more probably in old and fragile swimmers than on young and trained athletes. There's nothing exceptional to this part. The problem is when Hof adds his spiritual twist to it. Dikipewia (talk) 17:06, 1 April 2017 (UTC)

A lot of what Wim Hof says doesn't make sense, but what matters is if what he does is tested and verified. It's not all that different from how Jack LaLanne from the 1930s onwards was saying things that sounded like nonsense, he made claims that most experts at the time believed would be harmful to the body. E.g. he advocated exercising till failure, his arguments for it was of a pseudoscientific nature while the counterargument that this would be damaging to the body sounded a lot more reasonable from a scientific point of view. But what matters is empirical evidence and Jack laLanne won hands down in that contest. Exercise till failure is now recognized as a very effective way to build up muscle strength. Arnold Schwarzenegger explains here how he used such methods to his advantage. But if you take what he says literally, then a lot of that is pseudoscience. What he says about "shocking your muscles" cannot be taken seriously, but what matters is that the training method he argues for does work. Why it works is a totally different story that medical experts can now explain better. Count Iblis (talk) 18:03, 1 April 2017 (UTC)

One difficulty with dropping heat production is that many of the biochemical reactions in the body generate heat. Many such processes, such as those involved in contraction of the muscle cells in the heart, can't be switched off in order to drop heat production. Klbrain (talk) 23:26, 1 April 2017 (UTC)