Wikipedia:Reference desk/Archives/Science/2017 October 9

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October 9

How much effect do humans have on tides, wind, Earth's rotation and the Moon's position?

How many millimeters less are the tides in some places because of anthropogenic things like tidal power plants? How many millimeters/seconds of arc late or early is the Earth's rotation and Moon's position because of tidal power plants, humans moving things around affecting the rotational inertia, melting ice faster and so on? How big is the biggest zone with average wind reduction ≥0.1kph or ≥1kph from windmills? Sagittarian Milky Way (talk) 00:06, 9 October 2017 (UTC)

According to [1] the Three Gorges Dam changed the length of the day by 60 nanoseconds and moved the North Pole by nearly an inch. Wnt (talk) 10:03, 9 October 2017 (UTC)

Windmill spacing involves something called "array loss", which is the "obstacle shade" and/or effects of turbulence. [2] With that source I am not very clear whether it is loss of power that is 10% at 8-10 times the rotor diameter downwind, or something else. Wnt (talk) 12:42, 9 October 2017 (UTC)

King Canute made no difference. Blooteuth (talk) 15:42, 9 October 2017 (UTC)

Which goes to prove he was the king of Denmark but not Holland! Wnt (talk) 11:58, 10 October 2017 (UTC)

Neither did Barack Obama. And as for Algor.... At least Knut knew he was impotent and ignorant. μηδείς (talk) 21:06, 10 October 2017 (UTC)

Conservation of energy

Per the law of conservation of energy, energy can neither be created nor destroyed. This doesn't seem to be entirely true. One can create kinetic energy by spinning a fidget spinner and then "destroy" that energy by stopping the spinner. 212.180.235.46 (talk) 17:06, 9 October 2017 (UTC)

Stopping the spinner doesn't "destroy" energy -- it is transferred to (or absorbed by) your finger -- you can "feel" this; and you don't "create" energy, you transfer it from the energy of your finger muscles to the spinner. 2606:A000:4C0C:E200:29AF:8B75:2D37:5BB4 (talk) 18:12, 9 October 2017 (UTC)

Absorbing effectively means destruction, because the energy disappears and is no more. If the spinner is attached to an electricity-generating motor, the electric diode/bulb powered from it will stop shining, since the input from spinner has stopped. 212.180.235.46 (talk) 18:21, 9 October 2017 (UTC)

No. The heat and light radiated from the diode/bulb have knock-on effects such as raised local temperature and electromagnetic radiation rerspectively. Understand from the already linked article that energy is conserved within an Isolated system enclosed by walls through which neither matter nor energy can pass. Within that system one can have conversions between Potential energy and Kinetic energy (the OP's spinner). Blooteuth (talk) 18:43, 9 October 2017 (UTC)

Re: destruction of energy. A moving car has potential→kinetic energy; when it smashes into a wall, that energy isn't destroyed, it is used to bend metal, break glass, etc. (do not try this at home). With a spinner, the energy is transferred to whatever stops the spinner, where it is converted to some other form of energy; for example, your finger becomes slightly pushed-in -- which you can feel. If you use something like a pencil, some of that energy becomes sound ("click"). 2606:A000:4C0C:E200:29AF:8B75:2D37:5BB4 (talk) 18:59, 9 October 2017 (UTC)

No. A moving car has kinetic energy given by ${\begin{smallmatrix}{\frac {1}{2}}mv^{2}\end{smallmatrix}}$ as explained in Kinetic energy. Blooteuth (talk) 22:54, 9 October 2017 (UTC)

Oops, you're right! -- but a moving car could be considered a collection of parts each having potential energy. 2606:A000:4C0C:E200:29AF:8B75:2D37:5BB4 (talk) 23:07, 9 October 2017 (UTC)

... when they are lifted by the crane at the scrapyard? Dbfirs 06:46, 10 October 2017 (UTC)

That too -- see also: Elastic potential energy. 2606:A000:4C0C:E200:9C22:2C7C:65A6:B9DA (talk) 08:09, 10 October 2017 (UTC)

My car doesn't have much elastic in it, but I suppose there is a trace of stored energy in some of the materials. Dbfirs 10:00, 10 October 2017 (UTC)

When the spinner stops, its kinetic energy is converted into thermal energy. A small part of the spinner becomes a little bit warmer. This video demonstrates that heat is produced when objects collide. On a larger scale, the same thing happens when you use brakes to stop a car. C0617470r (talk) 20:48, 9 October 2017 (UTC)

In this case (stopping a spinner) the amount of energy converted to heat is negligible compared to that of deflection on your finger, assuming that is what is used to stop it. 2606:A000:4C0C:E200:29AF:8B75:2D37:5BB4 (talk) 22:27, 9 October 2017 (UTC)

If it is not forcibly stopped, energy will eventually be converted to heat from moving parts rubbing against each other (friction in the bearings) and by air molecules bumping into the spinner, and each other (air friction) -- also sound energy (if you hear a whirring sound from the moving air or buzz from cheap bearings). 2606:A000:4C0C:E200:9C22:2C7C:65A6:B9DA (talk) 02:24, 10 October 2017 (UTC)

In general the problem is that a highly visible form of energy is dissipated over a large area, so becomes "invisible". An example is where air resistance slows a flying object. Immediately afterwards, a small amount of air is moving at high speed, so that's noticeable, but very quickly that becomes a huge amount of air moving extremely slowly, which is no longer obvious. StuRat (talk) 23:00, 9 October 2017 (UTC)

Also relevant: Energy transfer, but wiktionary: energy transfer might be better. 2606:A000:4C0C:E200:29AF:8B75:2D37:5BB4 (talk) 23:43, 9 October 2017 (UTC)

It was not destroyed. The Time Thieves stole it in the moment they froze you to do their nasty trixes! --Kharon (talk) 02:06, 10 October 2017 (UTC)

Most kinetic energy produced by mankind is eventually converted to thermal energy (heat, if you prefer.) There are many, many examples of kinetic energy, and gravitational potential energy, appearing to have been destroyed. The truth is that these losses are exactly matched by increases in thermal energy, and therefore energy is conserved. Perhaps the reason this seems incredible is that the loss of some kinetic energy (or potential energy) produces only a small increase in temperature in a small region. This small rise in temperature is very difficult to measure because heat quickly flows away from the warm area into the surroundings. Joule created a piece of equipment, now called Joule's apparatus, in which a falling weight turned a paddle in an insulated vessel containing water and a thermometer. See James Prescott Joule#The mechanical equivalent of heat. Joule was able to confirm that the loss of potential energy of the weight matched the increase in thermal energy of the water.

When children use their fingers to stop spinning toys, the loss of kinetic energy of the toys is equal to the increase in thermal energy in their fingers. But almost impossible to measure using a thermometer. Dolphin (t) 11:26, 10 October 2017 (UTC)

• The OP is making a common mistake here, which is to confuse work with energy. Work specifically is the displacement of an object by force. The object moves in a line with the direction of the applied force. The applied force can be supplied by one of two different forms of energy: what we call kinetic energy means the force causing the work is supplied by another object in motion, while the term potential energy means that the force is supplied by some other means (such as gravity or tension in a spring, or some such). There is another form of energy however, thermal energy, but what makes thermal energy different is that thermal energy is unsuitable for providing the forces necessary to produce work by itself (thermal gradients can cause work, but the thermal energy of moving molecules by itself cannot produce a force on an object). The reason why is fairly simple: both kinetic and potential energy have a directional component; an object in motion that strikes another object imparts a force in the direction it was already moving. A force like gravity imparts a force along a line in the direction to the point between the two objects (the barycenter) Those are both able to do work (move something) because they can apply an unbalanced force on the target object. Thermal energy by itself cannot do this because by definition, thermal energy is the energy of motion of individual molecules. And thermal energy is ALWAYS equal in all directions (this is called the Equipartition theorem, or at least, it is a simplified version thereof). Since the forces of the motions of all of the individual moving molecules cancels out, the thermal energy cannot of itself cause work, it cannot generate a net force on another object. Thus, when something like friction (i.e. rubbing your finger on a moving fidget spinner to slow it down) causes the object to slow down, there is an exactly equivalent increase in thermal energy. That thermal energy is no longer available to do work. It's not lost or destroyed, just in a form that cannot immediately do work. --Jayron32 12:00, 10 October 2017 (UTC)
• None seems to have done the Fermi estimate of the temperature increase, so here goes.

Assume the fidget spinner is made of aluminium (specific heat capacity 900 J/K/kg), that its mass is distributed approximately as three solid rods of length L=0.1m, and that it spins at $\omega =30rad/s$ (a bit less than 5 rotations per second). Its rotational kinetic energy is then given by $E={\frac {m}{6}}\omega ^{2}L^{2}$ (see rotational energy, moment of inertia and List of moments of inertia). If we entirely stop the spinner by instantaneously transferring all that kinetic energy to heat inside the spinner, the average temperature increase would be $\Delta T={\frac {E}{mC_{p}}}={\frac {\omega ^{2}L^{2}}{6C_{p}}}$.

With the numbers I took, it gives a 0.002°C increase, less than measurable with standard thermometers (let alone your hand). You can change the numbers a bit, but you will not get to a tenth of degree (within the range of commercial thermometers, but still too small for human perception) without already-stretched assumptions. Remember also that we assumed all the heat goes to the spinner, while in reality it would likely dissipate through the air and move around. Tigraan^{Click here to contact me} 19:31, 10 October 2017 (UTC)

How exactly are populations calculated by the minutiae?

Human population counters keep going up and up and up. Does anybody know who keeps track of them? How exactly do humans keep account of every single human? What if there is a human being conceived right now but is just not born yet and may even have to be aborted? Wars and fighting occur all the time. Sometimes, one may be stabbed, bombed, lit on fire, stoned, hanged, tortured to death, etc. Are the counters an overestimate or underestimate of the actual population size? And how come the majority of humans live in Asia? Since wealthy nations like Japan are aging and cannot replace the old, will they have to adopt foreign babies in order to keep the society running or just allow more liberal immigration policies? 140.254.70.33 (talk) 17:10, 9 October 2017 (UTC)

Who says Japan "cannot replace the old"? ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:19, 9 October 2017 (UTC)

Some comments on conduct for Bugs to consider

What did google tell you? I know that's not helpful, but it's what you often ask people when they ask questions here. And this isn't even your question. If want to learn about Japan and don't know how, maybe you should ask a new question. Let's pretend you did that, and then let's pretend you got good references rather than a bunch of flack from people who tell you to google or question your premises. Those good references would look like this: I would like to know what the basis for the OP's premise is, since he states it like it's a given. ←Baseball Bugs What's up, Doc? carrots→ 18:37, 9 October 2017 (UTC)

For demographics of Japan, and their well-known problems with too few young people, see our article Aging_of_Japan. For scholarly articles, see "Population Aging in Japan: Demographic Shock and Fiscal Sustainability". For popular news coverage, see "Japan's population to shrink by a third by 2065" or "Japan's population is falling faster than it ever has before". SemanticMantis (talk) 18:02, 9 October 2017 (UTC)

I wonder why the article you linked to considers "large-scale immigration" a "politically sensitive topic", whatever that means. Then again, there is one big problem with immigrants. They may not want to assimilate. I mean, there are Chinese immigrants and their descendants in Southeast Asian countries right now, and they still learn Chinese. So, if a large group of immigrants come looking for work, then it would be like having a country overtaken by foreigners, and in the end, Japanese will forfeit its own language to the foreigners in much the same way Taiwanese aboriginals assimilate among the Han Chinese or the Native Americans assimilating among Americans. 140.254.70.33 (talk) 20:08, 9 October 2017 (UTC)

Through population statistics, see this for example. The easiest way is just to sum up the results of most recent censuses in all countries. In practice, other factors also come into play. Brandmeister^talk 17:17, 9 October 2017 (UTC)

You may find World population estimates of interest. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:18, 9 October 2017 (UTC)

• Short answer: those counters do not account for minutiae. They are all "fake" in that regard. Instead, the counter is driven at a rate that varies according to a statistical model. The model, in turn, computed the current estimated growth rate based on statistics collected and published in the past. The model incorporates actuarial and demographic assumptions. -Arch dude (talk) 21:55, 9 October 2017 (UTC)

• Shorter answer: Those are just estimates. StuRat (talk) 22:34, 9 October 2017 (UTC)

• Or, as Paul Harvey used to say, "guesstimates". ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:00, 10 October 2017 (UTC)

Maybe we can describe a simplistic model to the OP to give him an idea?

For each country

1. Take the number of people from the last census P

2. Calculate the number of people that died for any known, long period and divide that by the number of days in that period. That gives you an average number of death per day D.

3. Calculate the number of babies that are born for any known, long period and divide that by the number of days in that period. That gives you an average number of birth per day B.

4 then do P + ((B-D) * number of days since last census)

then add all the countries.

That should give you an estimate for today. There are more advanced ways of course, with more data, more advanced maths, controlling for months with high birth rates, controlling for the rate of ageing of the population etc. --Lgriot (talk) 13:25, 10 October 2017 (UTC)

• • Yes, but after all that, you end up with a fixed set of rates of change. The actual "counter" is merely a computer program that increments the counter at this rate. For example, when you load the page [3]] you see a bunch of counters which are very impressively incrementing at high rates. If you look at the underlying page source, you find that the counters are being incremented by a script that is running in your browser on your computer. -Arch dude (talk) 14:06, 10 October 2017 (UTC)

Immunity against viruses by changing the way DNA sequences code to proteins and changing the DNA code so that the same proteins are produced?

Can we change Aminoacyl tRNA synthetase so that the translation from codons in transfer RNA to amino acids gets permuted, simultaneously with corresponding permutation in the DNA? So, the organism will continue to function, it will make exactly the same proteins, except that a virus cannot make copies of itself because its genetic code won't work in the organism. Count Iblis (talk) 22:58, 9 October 2017 (UTC)

Well, first of all, I personally cannot make it, because I don't have a laboratory or the expertise to manufacture stuff. So, the "we" in your question perhaps refers to you and your team? Anyway, any modification in an enzyme must mean a modification to the DNA in vivo. Modification to the DNA is possible in the form of thymine dimers, but that also means cancer. On the other hand, it is possible to manipulate the epigenetics of an organism, but if the root problem is genetics, then the individual is doomed. 50.4.236.254 (talk) 23:36, 9 October 2017 (UTC)

I would take "we" here to mean "humanity, collectively". StuRat (talk) 23:53, 9 October 2017 (UTC)

In principle, yes. In practice, making millions of single nucleotide polymorphisms to the DNA is beyond what is currently feasible. Looie496 (talk) 01:25, 10 October 2017 (UTC)

Making the changes could be possible with Gene therapy in the near future but the question implies the wrong premise that viri are a static thread. But completely to the contrary viri as species actually evolve/mutate very fast, simply thru their massive numbers, and thus they will adapt to anything eventually. Besides that, its not clear what consequences massive genetic changes thru gene therapy will cause. The well known programmer wisdom "never change a running system" is probably a good hint. Much more promising seems to keep learning from nature. For example why sharks seem almost immune to all diseases. --Kharon (talk) 02:01, 10 October 2017 (UTC)

As I read the OP's question, he's asking about changing the genetic code itself, not any particular gene. So, for example, CAU would no longer code for histidine but some other amino acid, and every other triplet would similarly code for a different amino acid than it currently does. This is a complex question. I recommend reading Douglas Hofstadter's essay "The Genetic Code: Arbitrary?" which can be found in his book Metamagical Themas. (And note the initials of the essay's title.) But as to whether, even if the code could be changed, it could be changed in an existing living organism, I'd say that it is extremely unlikely with any foreseeable technology. (BTW, the story that sharks are immune to all diseases, or that they don't get cancer, is a myth mostly propagated by hucksters selling shark cartilage and similar useless nostrums. [4]) CodeTalker (talk) 03:43, 10 October 2017 (UTC)

No matter how you did it, the altered tRNA would be a different molecule with different interactions. Maybe nothing known, but the interactions would still be different in an unpredictable way. Also, with most versions of the scheme the GC content of the DNA would change, affecting its bulk properties (for example the amount of energy it takes to break it apart and replicate). You would have to look at whether the new sequence created new transcription factor binding sites anywhere in all that coding sequence. Worse, you'd destroy old ones that were supposed to work together in a complex regulatory network. (It is comparatively uncommon but certainly not unheard of to have such sites in the coding sequence; obviously there are evolutionary constraints to forming them, but you'd find evolutionary constraints to getting rid of them also). And debugging all those effects ... means making more changes to more things. So we're talking about evolution, and therefore, not really the same organism with the same characteristics. Nor would the altered organism seem likely to breed with the parent (not without some insanely advanced level of biological innovation) so this is not merely an evolutionary change but a different species. So I'm going to say no, under the usual caveat that biology could always come up with something I didn't think of. Wnt (talk) 12:07, 10 October 2017 (UTC)

• User:Count Iblis' suggestion is brilliant--the only problem is getting from here to there. How do you bridge the intermediate stage? But regarding the arbitrariness of the genetic code, I was gobsmacked when I saw the implication, and raised my hand to ask the professor, "Doesn't that mean the code is arbitrary?" He asked me to stay after class. It was like figuring out I was queer during mass, Chicxulub, and that the sky god doesn't exist. μηδείς (talk) 20:55, 10 October 2017 (UTC)

The only problem is that, well, this isn't really true. The genetic code we have is nearly optimal for allowing arbitrary basepair sequences (i.e. transcription factors) within protein coding sequence, which happens often, in part due to the presence of overlapping genes, but more so because gene enhancers can exist downstream of the promoter. Going over this bridge is therefore implausible. Furthermore, there is something akin to but different from Iblis' scheme involving CpG islands - they get methylated in humans, a password that viruses need to adapt to or suffer consequences for not knowing via TLR9. Wnt (talk) 21:27, 10 October 2017 (UTC)

Wnt, It's not so clear to me why e.g. interchanging G with C, and/or A with T that permute within base pairs wouldn't work. Count Iblis (talk) 20:24, 12 October 2017 (UTC)

Because DNA is much more complex than simply encoding a list of proteins, there are a huge number of regulatory elements involved in DNA that are sequence specific. For example transcription factors which control when a given gene is transcribed recognize certain sequences so if you change the codons you will create a transcription factor which recognizes a domain that no longer exists. 204.28.125.102 (talk) 22:41, 12 October 2017 (UTC)

If you look at Expanded genetic code you'l see some work on the lines of the question. Dmcq (talk) 08:14, 13 October 2017 (UTC)