Wikipedia:Reference desk/Archives/Science/2018 January 14

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January 14

Nannostomus beckfordi in Rio Guapore?

I am having trouble finding info on whether Nannostomus beckfordi can be found in the Guaporé River. It seems commonly accepted that it inhabits the Madeira River and some of its tributaries, but I could not find a source mentioning the Guaporé River specifically. Surtsicna (talk) 11:01, 14 January 2018 (UTC)

Google suggests:

Nannostomus beckfordi Giinther. 14. Nannostomus ... The Rio Madeira-Rio Guapore collection consists of 31 individuals...

From:

• Weitzman, Stanley H.; Cobb, J. Stanley (1975). "A revision of the South American fishes of the genus Nannostomus Günther (family Lebiasinidae)". Smithsonian Research Online. Smithsonian Contributions to Zoology.

—But I haven't figured out how to find it. —2606:A000:4C0C:E200:1D4C:29E3:6313:60B3 (talk) 23:31, 14 January 2018 (UTC)

There is a PDF version available online but if I understand correctly, it refers to Nannostomus digrammi. Surtsicna (talk) 09:14, 16 January 2018 (UTC)

Accelerating towards the sun

I was watching this video and it discussed how to hit the sun, and it asserts you have to cancel your orbital velocity in order to fall into the sun. But why can't you just accelerate towards it? Or even just given an initial velocity towards the sun, won't you hit it eventually? The rocket should still have a velocity vector aimed right at the sun correct? And in outerspace there's no friction to slow down your vector towards the sun so I would assume that you can still hit the sun simply by heading towards it. ScienceApe (talk) 13:08, 14 January 2018 (UTC)

Your total velocity vector is relevant, not a possible component you add towards the sun. Note that the Earth is continually accelerated towards the sun (by the gravitational attraction of the sun), yet never hits it (*knocks on wood*). Qualitatively, you can see it this way: If you are in orbit around the sun, you have a significant velocity perpendicular to the line from you to the center of the sun. If you add a small vector along that line, by the time you would have reached the sun, you've moved very much sideways, so you miss. And the added velocity vector is not even pointing towards the sun anymore. On the other hand, if you just cancel your orbital velocity, gravitation alone will accelerate you to the sun, and you will hit it. --Stephan Schulz (talk) 14:49, 14 January 2018 (UTC)

(ec) Orbital mechanics can be counterintuitive sometimes. (If you have the time, money, and inclination, Kerbal Space Program provides a thoroughly frustrating and delightful insight into the problems of manoeuvering in space.)

"The rocket should still have a velocity vector aimed right at the sun...there's no friction to slow down your vector towards the sun..." The problem is that your impulse toward the Sun adds a component to your velocity vector that points towards the Sun at the time that it's applied, but your rocket keeps its original momentum 'sideways' (that is, in the direction of its original orbit, or prograde) as well. That new velocity component that points at the Sun now will be pointing tangentially to it a quarter orbit later, and away from the Sun half an orbit down the road. The overall effect is that you go from your original nearly-circular orbit to one that's more eccentric (more elliptical, or 'squashed' and cigar-shaped), but still stable.

Additional inward burns will change that eccentricity (make the 'cigar' narrower or fatter) and/or rotate the axes of the orbit around the Sun (change the direction the cigar points); the degree to which one or the other occurs depends on where you apply that thrust in the orbit.

In principle, if you apply enough inward thrust over a short enough period of time, you can squeeze that 'cigar' down to be narrow enough that rocket grazes the Sun instead of sliding sideways past—but that's way more expensive than doing a retrograde burn (i.e. 'cancelling' your orbital velocity to fall into the Sun). TenOfAllTrades(talk) 15:16, 14 January 2018 (UTC)

• Let me just point out the curious fact that it is possible to accelerate constantly toward the Sun (that is, always centripetally) without your orbit changing at all. If the equation a = v²/r holds, with a directed toward the Sun and v at right angles to the Sun, then you will move in an unchanging circular orbit. This actually shouldn't be a surprise, given that gravity creates a constant acceleration that is always directed toward the Sun. Looie496 (talk) 15:41, 14 January 2018 (UTC)

To try to give a more intuitive analogy, imagine you're in a boat in the middle of a river, being pulled by the current. You pick a point on one of the banks, at a ninety-degree angle to your direction of motion, and start moving towards it. By the time you reach the bank, you'll be downriver of the point you selected, because you continued moving with the current while you also moved towards the bank. In this analogy, the point on the river bank is the Sun, and your motion downriver is your previous trajectory relative to the Sun. Things move at high speeds in space, because there's nothing to stop them. It doesn't seem like it because our hard-wired intuition is designed for an Earth-bound environment; because the distances are so big and there's no "fixed" background to easily compare against, it looks like things in space are moving slowly if at all. For some numbers, the International Space Station, and other things in low Earth orbit, are moving at about 8 kilometers per second relative to you and me. That's much faster than a bullet fired here on the ground. They circle the Earth roughly every two hours. Similarly, we're all cruising around the Sun at about 30 kilometers per second. If you point yourself towards the Sun, you're still moving screamingly fast around it, and so (as noted above) you just wind up in a wackier orbit around it (because the Sun's gravity keeps you from flying off into deep space). Although, as TenOfAllTrades said, if you had infinite fuel you could eventually stretch your orbit out so much that you would take a dive into the Sun next time you went past, but there's no real point since that takes more fuel than the "right" way of adjusting your orbit. Also, depending on payload, there's no guarantee (very hot) stuff wouldn't pop back out the other side of the Sun, since you're just grazing the photosphere, which might be a problem if you were trying to get rid of whatever it was. This is one reason why the sometimes-raised idea of launching nuclear waste into the Sun isn't a good idea. This, I think, is good at explaining some more about orbits. --47.157.122.192 (talk) 10:24, 15 January 2018 (UTC)

This doesn't really seem very complicated to me. If you made a map of your present orbit, you're moving straight sideways relative to the sun. To hit the sun, the most straightforward way is to have your motion be straight at the sun. I mean, if you picture Captain Kirk on the bridge he wants to see the sun getting bigger and bigger, not moving right or left. And in order to do that, the ship has to counteract its present off-course motion. If your warp engines allow you to accelerate to a much faster speed than your current orbit, you don't even have to aim much to the side of the sun ... just enough to "correct" your course so you're moving right at it. Don't forget the sunblock! Wnt (talk) 20:02, 15 January 2018 (UTC)

Lying to children about science

When people teach children about complex phenomena like atoms (as composed by little balls orbiting around bigger balls) or DNA (as a building plan for living beings), could it be that we unwillingly making it more difficult to understand the real thing later on? Couldn't it even be that we are making them believe crazy stuff? --Hofhof (talk) 20:33, 14 January 2018 (UTC)

Would you start elementary reading classes by having them read Shakespeare? Or would you go for simpler stuff that they can more easily grasp? ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:42, 14 January 2018 (UTC)

Don't "people" teach children that this was what was once believed, or that this is a first approximation? All scientific models eventually turn out to be approximations. This doesn't make them lies. Dbfirs 20:48, 14 January 2018 (UTC)

The aricle you linked in the header discusses at length the value of the method, the risks, and the importance of choosing the correct lie to help learners get started but not get too misled for later learning. It even uses DNA as a specific example. DMacks (talk) 20:53, 14 January 2018 (UTC)

Maybe. As our article you linked to states, however, 'Worstall stressed that this form of educational methodology was ubiquitous across multiple academic disciplines: "This is true of any form of education by the way. We don’t start music classes with atonality, we start with simple scales. We don’t do syncopation until we’ve mastered 2/4 and 4/4. Einstein’s corrections at the margin to Newton come quite late in a physics education."' In other words, whether it leads to wrong-thinking or not, it is pretty much the standard way to teach everything... everywhere. Reality is horribly complicated; people would get lost if you started the ABCs with discussions about phonetics. Matt Deres (talk) 22:11, 14 January 2018 (UTC)

On the contrary, teaching a simple model can make it easier, not more difficult, to understand a more complex model later. If we don't teach simple models, then the human brain makes its own model, and can often get it even more wrong. Dbfirs 22:20, 14 January 2018 (UTC)

This is the right way. 00:16, 15 January 2018 (UTC) — Preceding unsigned comment added by Count Iblis (talk • contribs)

I would start by teaching scientific method, for young children just hypothesis and test (salt will dissolve in water but sand won't, maybe asking them about some less familiar substances). Then as they get older teach them about hypotheses, laws, and theories. That way, when you teach simplifications they will realise that these are not "lies" but hypotheses and laws that have actually been refined. I think a great example is Newtonian physics, and how it can be used to land a man on the moon, but not explain things like gravitational lensing. -- Q Chris (talk) 08:58, 15 January 2018 (UTC)

Thanks, Count Iblis! Joepnl (talk) 00:47, 18 January 2018 (UTC)

• Well, the word "like" exists. Children have no problem understanding that chocolate is like hard cheese or butter in a way that it is not like broccoli or spinach. They can understand at about age 6-7 that there are difficult ideas that you have to learn first before you can understand even more complex ideas.

I remember being annoyed that the only thing adults would tell me about Watergate was that I would understand when I was older, and I remember being told the basics of stoichiometry and algebra at age 8 with the ability to see it worked, even if I hadn't automated the more basic concepts yet that you needed to master to move on to those harder ones.

There is absolutely no a priori reason to believe that scientists believe that particles are billiard balls. Billiard balls are both mechanically disruptible and exist on a hugely different scale. Some people do get English degrees and become science journalists, but there's no reason to believe we are all confused as they are. I suggest Ayn Rand's Introduction to Objectivist Epistemology, especially the chapter on "Abstractions from Abstractions". μηδείς (talk) 03:18, 16 January 2018 (UTC)

When I was in primary school the music teacher told us that a crotchet was one beat. Some time later she said that the beat depended on the music (this is discussed in the second sentence of the article lead). I said she must have got it wrong, because we had always been told it was one beat. She then said that she had only told us this initially because it was simpler to understand. I asked her if this was explained in a book anywhere and she showed me a copy of Rudiments of Music which appeared to cover the theory in great detail, and sure enough it was as she said. 195.147.104.148 (talk) 21:11, 16 January 2018 (UTC)

It is important to develop trust with students, and I make it a point always to explain when I am using simple examples, analogies, rules of thumbs, when exceptions are known, that an idea is heuristic, etc. One of my favorite legal writers is absolutely brilliant as both a legal writer and thinker and extemporaneous speaker, and her knowledge is so broad that I find it absolutely incredible that she neither believes in nor can explain evolution, although she graduated from a well-regarded secular secondary school and has a JD.

I suspect that at some point she was told a falsehood--maybe something like "monkeys eveolved into people"--as a fact when it is shorthand for saying that monkeys and humans have the same ancestors. This same problem makes it impossible for my otherwise quite intelligent mother to understand why the rest of the monkeys aren't currently also evolving into people, if monkeys really do "evolve into people". Pedagogy is much too dangerous to be left to the professionals. μηδείς (talk) 21:51, 16 January 2018 (UTC)

Removed sock puppet irrelevance. The source addresses the issue, ad hominem nonsense is nonsense. μηδείς (talk) 03:04, 21 January 2018 (UTC)

No more of a joke than the original premise of this section. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:15, 17 January 2018 (UTC)

My undergrad advisor read this work and was highly impressed, and had never heard of the author. My ex-advisor is also Daniel Dennett's bibliographer, as well as a colleague of Searle and many others like the late John Hospers and Murray Rothbard. Arguments by ad hominem are self refuting, beneath contempt. I'm done with that here. The text is available by pdf and about 100pp. Those who are afraid to read it should be. μηδείς (talk) 03:04, 21 January 2018 (UTC)

So if DNA is not a building plan, what's the use? Even scientists at the very edge of science need to have some sort of model. Science didn't skip Atomism to reach the current state of quantum mechanics, and we probably wouldn't get much further without studying the current model even when we know that we're still looking at a model that can't possibly be describing the full truth. I think kids follow the same path. Joepnl (talk) 22:38, 17 January 2018 (UTC)

References