Wikipedia:Reference desk/Archives/Science/2022 December 11

= December 11 =

When a high-speed alpha particle hits a gold nucleus, does the gold nucleus remain stationary?
In the Geiger-Marsden experiments, the alpha particle can receive the entire changes of momentum if the gold nucleus remains stationary.
 * $$\Delta p = F \Delta t = k \cdot \frac {Q_\alpha Q_n}{r^2} \cdot \frac {2r}{v_\alpha}$$

Otherwise, the KE gained by the gold nucleus must equal the KE lost by the alpha particle. Vze2wgsm1 (talk) 12:29, 11 December 2022 (UTC)


 * It's not at all clear what your question is. The equation you've posted IS the change of momentum in the alpha particle under a classical mechanical description of the collision as an elastic one between two spheres.  There is ALSO a change in momentum of the gold atom, and a corresponding change in kinetic energy of each. And yes, as long as you consider this an elastic collision, then kinetic energy is conserved. PianoDan (talk) 18:03, 11 December 2022 (UTC)
 * Rutherford's gold foil experiment, performed by Geiger-Marsden, is the basis of believing an atom has a nucleus. Rutherford used the above equation to claim that an alpha particle collision with a gold nucleus can reverse the alpha particle's momentum.  In other words, Rutherford may have made a false assumption.  The alpha particle's deflection by more than 90 degrees may have been via collision with a multi-atom molecule, instead of a collision with the nucleus of a single gold molecule. Vze2wgsm1 (talk) 22:46, 11 December 2022 (UTC)
 * Gold molecules? Au3O4? Given a model for the atom, one can compute the predicted distribution of the angles of deflection of the emerging alpha particles. This is not about the occasional stray particle, but about substantial numbers. If the observations differ too strongly from the theoretical model, and experimental or calculation errors can be ruled out, the model was wrong. --Lambiam 01:46, 12 December 2022 (UTC)
 * The calculation predicting the angles of deflection assume that gold nucleus (qn) remains stationary while the alpha particle approaches and leaves the gold nucleus.
 * $$s = \frac {Xnt\csc^4{\!\left(\tfrac {\phi}{2}\right)}}{16r^2} \cdot {\left(\frac {2Q_n Q_{\alpha}}{mv^2}\right)}^2$$
 * Acceleration of qn removes KE from the alpha particle and changes the angle of deflection Vze2wgsm1 (talk) 02:47, 12 December 2022 (UTC)
 * I don't get what you are trying to argue, other than that you seem to think Rutherford and his team (and the many teams who replicated the experiment) were stupid and overlooked something big, like the presence of Blue Meanies imparting motion to the gold nuclei. --Lambiam 05:18, 12 December 2022 (UTC)
 * If you think that Rutherford's calculations of alpha particle deflection do not assume a stationary gold nucleus, then either mathematically prove your point, or show how a gold nucleus can indeed remain stationary while a high-speed alpha particle approaches. I wish you luck. Vze2wgsm1 (talk) 09:54, 12 December 2022 (UTC)
 * It's called an approximation, and it's made because a gold nucleus is about 50 times as massive as an alpha particle. Do you think that approximation is unjustified and therefore everything we know about atoms and nuclei is wrong? Because nobody's done any more experiments since Geiger-Marsden? Or done any more sophisticated analysis of scattering experiments than Rutherford in the last hundred years? --Wrongfilter (talk) 10:17, 12 December 2022 (UTC)
 * Thanks PianoDan. I appreciate your comment on the equation.  Another equation from the Geiger-Marsden experiments article indicates the alpha particle receives the entire change of momentum when an alpha particle approaches a gold nucleus.  When a high-speed alpha particle hits a gold nucleus, does the gold nucleus remain stationary?
 * \theta \approx \frac {\Delta p}{p} < k \cdot \frac {2Q_\alpha Q_n}{m_\alpha r v_\alpha^2}
 * $$ Vze2wgsm1 (talk) 11:39, 12 December 2022 (UTC)
 * It remains stationary enough. Remember a couple of things about the transfer of momentum of the alpha particle to the gold atoms in the experiment 1) the alpha particle is 1/50 the size of the gold nucleus, so that needs to be taken into account.  But MOST IMPORTANTLY, 2) the gold atoms are bound up in a solid crystal lattice.  Yes, if the gold atoms were in the gas phase, we would expect a transfer of kinetic energy on something like a one-to-one relationship.  However, the gold atoms are bound up with each other in a solid matrix.  What that means effectively is that the transfer of energy is distributed across the entire sheet of gold foil rather than to 1 gold atom.  A single alpha particle, even a really fast moving alpha particle, transferring some of its momentum to trillions upon trillions of gold atoms has essentially no effect on the gold.  We can treat the gold atoms as stationary, because they essentially are; any displacement of the gold nucleus by interaction with an alpha particle is so many orders of magnitude smaller than the size of the nucleus itself, it is functionally nil.  -- Jayron 32 12:56, 12 December 2022 (UTC)
 * I'm not so sure about the lattice argument. Atoms in a crystal do oscillate about their mean positions, and a collision will excite crystal vibrations (phonons on a quantum level). The transferred energy will ultimately dissipate away, and the momentum transfer to the entire gold foil is obviously negligible, but that does not make it necessarily so in the individual scattering process, which is what is relevant here. I'm not well versed in crystal and solid state physics, but my gut feeling suggests that it ought to be more appropriate to treat the gold nuclei as free particles rather than being fixed in a crystal lattice (actually, do nuclei know that they live in a crystal?). Which brings us back to the mass ratio of 50 that again makes a stationary gold nucleus a good approximation. --Wrongfilter (talk) 14:57, 12 December 2022 (UTC)
 * Yes, but the important thing is it will not excite one single atom alone; such excitations are dispersed through the lattice of gold atoms. The OP sounds like their major objection is that the fact that when interacting with the alpha particle, the singular gold atom would experience some kind of measurable displacement in order to itself redirect the alpha particle; the fact that the specific gold atom does not itself appreciably change momentum means that something is wrong with Rutherford's theory.  I was explaining why that was at fault; the momentum transferred to any one gold atom is dissipated through the system via the chemical bonds between gold atoms; yes that dissipation does all sorts of complex things to the lattice of gold atoms; but that's irrelevant.  The OP's statement "Rutherford used the above equation to claim that an alpha particle collision with a gold nucleus can reverse the alpha particle's momentum" is based on some sort of model of the gold nucleus as a gas particle of some sort, the assumption the OP makes is that Rutherford's model presupposes the gold nucleus absorbs the alpha particle's momentum without itself doing anything with that momentum, violating the law of conservation of momentum.  This assumption on the part of the OP seems to be that the interacting gold nucleus is not dissipating the absorbed momentum through the lattice (in all the ways I glossed over but that you describe).  That's what they are not understanding here.  That's why the gold nucleus remains stationary; or at least can be treated like it remains stationary, even if at levels below the level of measurement, it probably does shimmy a little bit.-- Jayron 32 15:23, 12 December 2022 (UTC)
 * I still disagree: the dissipation happens on a time scale that is longer than the time scale that is relevant for the individual scattering process. Staying classical (and we'd need to get quantitative to see whether that is justified), in my view the nucleus ought to be treated as a free particle which does absorb a bit of momentum (not enough to significantly alter Rutherford's conclusions, mind!). This is then transferred to the electron shell of the atom and then to the lattice as a whole. But when this happens the alpha particle is already on its way and is not affected any more. For the time scales I'd look at the speed of the alpha particle vs. the sound speed in the crystal. --Wrongfilter (talk) 15:35, 12 December 2022 (UTC)
 * That's fair. I concede.  Still, it is perplexing that, for the second time in as many weeks, the OP thinks that with almost no in-depth reading of the physics involved in the Rutherford/GM experiment and its conclusions, they're somehow going to play "gotcha" and take down over 100 years of atomic theory so simply.  -- Jayron 32 16:12, 12 December 2022 (UTC)
 * I'll also point out that if atoms don't have nuclei, then I'm out of a job, since I work in nuclear medicine, and my entire livelihood is based on confirming every single day that our understanding of the nucleus is more or less correct. :) PianoDan (talk) 15:31, 12 December 2022 (UTC)
 * How do you define nucleus and what is your best evidence that an atom has a nucleus? If you define nucleus as the thing that is left over after all electrons are stripped away from an atom, then I agree with you.  The thing that is left over can have volume and chemical reactivity of an atom or molecule.
 * If you define nucleus as a small structure within an atom, then I wonder how adding a single electron to a stripped nucleus can convert the stripped 'nucleus' into a small structure within an atom? Vze2wgsm1 (talk) 13:27, 13 December 2022 (UTC)
 * Thanks Jayron32. The gold can ionize, which is an inelastic collision.  Typical of high-speed alpha particle collisions. Vze2wgsm1 (talk) 21:56, 12 December 2022 (UTC)
 * Thanks Jayron32. When an alpha heads toward a stationary gold, and if both the gold and the alpha are free, then during every instant, and at every distance between them, the repulsive force between the alpha and the gold is EQUAL and mutual.
 * $$m_1a_1=m_2a_2$$
 * The mutual force causes the KE lost by the alpha to equal the KE gained by the gold, regardless of the difference in mass. The alpha simply loses KE. Vze2wgsm1 (talk) 20:42, 12 December 2022 (UTC)
 * That is simply Newton's third law of motion. PianoDan (talk) 21:20, 12 December 2022 (UTC)
 * The point is that a high-speed alpha will not reverse direction when the alpha approaches a free gold nucleus, regardless of the difference between alpha mass and gold mass. Rutherford had to assume a stationary gold, to get Newton's third to reverse the direction of the alpha. Vze2wgsm1 (talk) 05:38, 13 December 2022 (UTC)
 * Yes, it will reverse direction. Let's look at the one-dimensional problem, central collision of point particles, forward or backward scattering only. We need to satisfy conservation of momentum and of energy, and we write the energies and momenta before and after the collision at infinite separation (large enough that the Coulomb energy is negligible). First, momentum:
 * $$ m_\alpha v_i = m_g v_g + m_\alpha v_f$$, i.e. $$v_g = r (v_i - v_f)$$,
 * where I've defined the mass ratio $$ r = m_\alpha/m_g \approx 1/50$$. Now for energy (the factors 1/2 cancel, and I won't bother to write them out):
 * $$m_\alpha v_i^2 = m_g v_g^2 + m_\alpha v_f^2$$.
 * Inserting $$v_g$$ and rearranging gives the quadratic equation
 * $$(r+1) v_f^2 - 2r v_i v_f + (r-1)v_i^2 = 0$$.
 * This has two solutions. The first is $$ v_f = v_i$$ and $$v_g=0$$, which corresponds to no collision, this is uninteresting. The second solution is
 * $$ v_f = \frac{r-1}{r+1}v_i$$, hence $$v_g = \frac{2r}{r+1}v_i$$.
 * With $$r\approx 1/50$$, the velocity $$v_f$$ of the alpha particle is negative, i.e. reversed. The velocity of the gold nucleus is $$v_g \approx 0.039 v_i$$, so it does pick up a bit of velocity, which is of course reflected in the fact that the speed of the alpha particle is a bit lower than initally, $$|v_f| < |v_i|$$, but clearly in the opposite direction. This is very basic physics. --Wrongfilter (talk) 11:31, 13 December 2022 (UTC)
 * @Wrongfilter's analysis is correct. And if you want to just visualize it - if you put a bowling ball on an ice covered pool table and hit the cue ball towards it, would you REALLY be surprised if the cue ball came back towards you?  Because that is more or less exactly what is happening here. And yes, the bowling ball DOES move a bit away from you in that case. PianoDan (talk) 17:14, 13 December 2022 (UTC)
 * Thanks Wrongfilter.
 * 1. KE is conserved, due to conservation of energy. Momentum is not necessarily conserved.
 * 2. If gold is free and initially stationary, then the KE lost by the alpha will equal the KE gained by the gold, regardless of the difference in mass. If alpha KE somehow became zero (before reversing direction), then the gold would contain total KE. Afterwards, adding KE to the alpha requires removing KE from the gold.
 * 3. If gold remains stationary, then when the alpha particle slows to zero (before accelerating in the opposite direction) total KE equals zero. Vze2wgsm1 (talk) 22:11, 13 December 2022 (UTC)
 * Momentum is, in fact, necessarily conserved. TOTAL energy is also conserved. If this were an elastic collision between two solid spheres, then kinetic energy would also be conserved at all times, yes.  In that (simplified) model, you would have an instantaneous transfer of (some) energy from the alpha particle to the gold nucleus at the moment of collision, and an instantaneous change of direction.
 * Worth pointing out, however, that in the nuclear case, there is also POTENTIAL energy to be considered, in the form of the Electric potential energy between the positively charged alpha particle and nucleus, which stores energy as the two particles approach, and returns it to the two particles as they separate.  PianoDan (talk) 23:01, 13 December 2022 (UTC)
 * Thanks PianoDan.
 * 1. Conservation of momentum requires an environment not acted on by external force. The electrostatic force between the alpha and the gold is an external force.
 * 2. Nobody assumed collisions or other instantaneous changes of direction. Electrostatic repulsions are not necessarily collisions.
 * "If this were an elastic collision between two solid spheres, then kinetic energy would also be conserved at all times, yes. In that (simplified) model, you would have an instantaneous transfer of (some) energy from the alpha particle to the gold nucleus at the moment of collision, and an instantaneous change of direction."
 * 3. You do realize that Rutherford's calculations are based on the electric potential energy between an alpha particle and a gold nucleus.
 * "there is also POTENTIAL energy to be considered, in the form of the Electric potential energy"
 * Vze2wgsm1 (talk) 01:17, 14 December 2022 (UTC)
 * The electrostatic force between alpha and gold is an internal force in the system that we consider here. External forces might come from the gold lattice, for instance, but we've discussed at length why those forces can be neglected here. You might worry, incidentally, about alpha particles that excite gold atoms. In this case, kinetic energy would be lost to internal degrees of freedom and that would have to taken into account. But: these inelastically scattered particles are not measured in the Geiger-Marsden experiment, only the elastically scattered ones are. I also explained why potential energy did not appear in the energy equation that I used. There is no need to consider the dynamic details of the scattering process (aka collisions), we only need to look at the initial and final states. --Wrongfilter (talk) 06:18, 14 December 2022 (UTC)
 * Thanks Wrongfilter. Forces like gravity and electrostatic are both external and internal. When force causes acceleration, then KE and momentum change.   Momentum = mass x velocity. Vze2wgsm1 (talk) 11:08, 14 December 2022 (UTC)
 * So what? --Wrongfilter (talk) 11:16, 14 December 2022 (UTC)
 * PianoDan's assumption of conservation of momentum conflicts with acceleration due to electrostatic force.
 * $$m_\alpha v_i^2 = m_g v_g^2 + m_\alpha v_f^2$$
 * Are you claiming that alpha particle deflection is indeed governed by conservation of momentum? Vze2wgsm1 (talk) 11:40, 14 December 2022 (UTC)
 * Yes, of course it is. And if you think it isn't then any further discussion is useless. --Wrongfilter (talk) 12:08, 14 December 2022 (UTC)
 * I accidently put PianoDan's KE equation instead of his momentum equation in my previous post. I should have used the following equation to show that PianoDan indeed assumed conservation of momentum:
 * $$ m_\alpha v_i = m_g v_g + m_\alpha v_f$$, i.e. $$v_g = r (v_i - v_f)$$
 * An example that shows momentum is not conserved is:
 * When the alpha has high velocity, the alpha has high momentum and gold has zero momentum and remains stationary. When the alpha stops while reversing direction, the alpha will have zero momentum and the gold will have zero momentum.  Total momentum was initially high, and then became zero.
 * Note: If you cannot defend your conservation of momentum idea, then my next step is alteration of the Geiger–Marsden experiments article to highlight Rutherford's assumption of zero gold velocity. Vze2wgsm1 (talk) 12:52, 14 December 2022 (UTC)
 * I wrote down that equation, not PianoDan. And your example is utterly wrong. Any momentum lost by the alpha particle is taken up by the gold nucleus, so that total momentum is conserved. Do not edit the article, any changes you make will be reverted. --Wrongfilter (talk) 13:06, 14 December 2022 (UTC)
 * Ok, what can I say and what can't I say? Vze2wgsm1 (talk) 13:21, 14 December 2022 (UTC)
 * If you wish, I can use the talk page. I request participation from uninvolved, interested editors. Vze2wgsm1 (talk) 13:28, 14 December 2022 (UTC)
 * Your comment: "Any momentum lost by the alpha particle is taken up by the gold nucleus" conflicts with the stated condition that gold nucleus remains stationary. Please explain.
 * Does your comment: "Do not edit the article, any changes you make will be reverted" indicate that Wikipedia found justification to ban me from making any comments on article? What was the justification? Vze2wgsm1 (talk) 14:17, 14 December 2022 (UTC)
 * The gold nucleus gains momentum in the same way that a brick wall takes up momentum when you hit it with your fist. Conservation of momentum is not negotiable. However, as has been said before, the resulting speed of the nucleus is small because of its high mass. As an approximation it is therefore justified to neglect that speed and to assume that the nucleus remains stationary. As regards the article: you can of course put in anything that is properly sourced with reliable external references, anything else not. --Wrongfilter (talk) 14:29, 14 December 2022 (UTC)
 * Any movement of the brick wall conflicts with the (absolutely) stationary gold criteria. If the gold remains stationary, then the KE of the alpha converts entirely into electrostatic potential energy by the time the alpha becomes stationary.  Otherwise, the alpha KE would be divided between gold KE and electrostatic potential energy.
 * I will make sure that any edit I make to a Wikipedia article contains the proper references. Vze2wgsm1 (talk) 15:16, 14 December 2022 (UTC)
 * You keep missing the point, so I'll try to restate it, as others have, yet again. There is a difference between "doesn't move enough to factor into our calculations, so we'll treat it like it is stationary" and "really-for-real-honest-to-God-didn't-move stationary".  As everyone here keeps telling you, when we (and everyone else except you) are saying "stationary", we're referring to the first situation, NOT the second.  You keep hearing us tell you the first, and keep arguing against the second, which no one except you is claiming.  Yes, the gold nucleus absorbs some of the momentum of the alpha particle.  However, it does not absorb enough to make a difference, so we treat it like it's stationary.  The mosquito that slams into my car windshield while I am driving down the road also imparts a momentum on my car, but I'd be stupid to spend any effort calculating how much it altered my car's speed.  -- Jayron 32 16:01, 14 December 2022 (UTC)
 * To provide evidence that a gold nucleus can act like a free particle, I present the following video. The video contains the math for deflection of an alpha particle and a FREE gold nucleus.
 * https://www.youtube.com/watch?v=5V_1oVbrWLs
 * Note: I do not claim that deflection from electrostatic repulsion is the same as deflection via a collision. Vze2wgsm1 (talk) 19:47, 14 December 2022 (UTC)
 * That video does indeed contain the math for the interaction between a free nucleus and an alpha particle, because that is a simple problem to solve, and the video is a solution to a problem in a first year college physics textbook. It is not evidence that a gold nucleus can act like a free particle, because that is taken as a starting assumption of the problem. PianoDan (talk) 23:36, 14 December 2022 (UTC)
 * Also, since PianoDan has made the point that a contrived problem for the purpose of demonstrating how to do a calculation is not a statement on how the physics of the Rutherford gold foil experiment actually worked, I will just note that "deflection from electrostatic repulsion is the same as deflection via a collision" is a nonsensical statement. Collisions are electrostatic repulsions; whether we're talking two balls rolling on a billiards table and colliding (where the force of the collision is mediated by the electrostatic repulsion of the electron clouds of the atoms at the surface of each ball) or where we're talking about the collisions of fundamental particles, where the collision is described by Quantum electrodynamics and things like Feynman diagrams and Path integral formulation and the like.  -- Jayron 32 13:48, 16 December 2022 (UTC)
 * If I drop a heavy and a light ball from the leaning tower of Pisa, both hit the ground at the same time, with the heavy ball gaining the most KE.
 * The force on the alpha and the gold is mutual and the total time the force is applied is the same. Vze2wgsm1 (talk) 13:35, 16 December 2022 (UTC)
 * The video got it right. because both the gold and the alpha got equal KE. The answer to my question was that gold indeed acquires KE equal to alpha.  The Geiger-Marsden experiments article contained calculations that use force at a particular distance for an increment of time to calculate change of momentum.  The change of alpha momentum could be a function of if the gold gained KE or not.
 * The leaning tower of Pisa is another complication of how forces act. Equal gravitational force acting on particles with different masses can continuously give more KE to the heavier mass. Equal electrostatic force between particles with different masses can continuously add equal KE to both particles. Vze2wgsm1 (talk) 15:13, 16 December 2022 (UTC)
 * Correction: Some say electrostatic force causes equal KE, others say equal momentum. Not picking sides.  The alpha particle's change of momentum is a function of the gold's change of velocity.
 * $$\Delta p = F \Delta t = k \cdot \frac {Q_\alpha Q_n}{r^2} \cdot \frac {2r}{v_\alpha}$$
 * Vze2wgsm1 (talk) 15:53, 16 December 2022 (UTC)
 * I have no idea what you are talking about with "some say". There are no sides here - there's just physics.
 * Momentum is conserved. The total momentum of the system is the same before and after the collision.
 * Kinetic energy is conserved. The total kinetic energy of the system is the same before and after the collision.
 * The statement "Equal gravitational force acting on particles with different masses..." doesn't make sense, because the gravitational force between two objects is DEPENDENT on their mass, and is therefore not equal for particles of different masses in the same field. (See the article on gravity). The reason the acceleration for two objects dropped off a twoer is the same, is that the mass of the body in the equation of motion $F = m_{obj}a$  is cancelled by the mass of the body in the equation of the force of gravity $F = G \frac{m_{obj} m_{earth}}{r^2}$.
 * So $a = G \frac{m_{earth}}{r^2}$ in all cases where the change of r can be neglected (i.e., any tower you care to drop a ball from in Renaissance Italy), even though F (and therefore the change in momentum and kinetic energy) is dependent on the mass of the object.
 * And it's also completely unclear what dropping balls off a tower has to do with the gold foil experiment. PianoDan (talk) 17:00, 16 December 2022 (UTC)
 * So $a = G \frac{m_{earth}}{r^2}$ in all cases where the change of r can be neglected (i.e., any tower you care to drop a ball from in Renaissance Italy), even though F (and therefore the change in momentum and kinetic energy) is dependent on the mass of the object.
 * And it's also completely unclear what dropping balls off a tower has to do with the gold foil experiment. PianoDan (talk) 17:00, 16 December 2022 (UTC)

Where in digestion does salt and sugar separate?
Human urine is 95% water, then urea at the next largest, followed by the salt ions of sodium, chloride, and potassium. And so, urine is salty, even if you eat lots of sweet food doesn't make urine more sweet. So that means sugar goes the other route. Sugar is covalent, so covalent foods go the other route, ionic foods go to the urine. Where is that separated? In the liver, blood vessels? Thanks. 67.165.185.178 (talk) 14:19, 11 December 2022 (UTC).
 * Sugar is metabolized by insulin. The presence of sugar in urine is a symptom of diabetes.  Acroterion   (talk)   14:22, 11 December 2022 (UTC)
 * So that happens in the pancreas? And the salt continues to the blood vessels, then to kidneys? 67.165.185.178 (talk) 14:33, 11 December 2022 (UTC).
 * No, the pancreas supplies the insulin, which is used throughout the body. Read carbohydrate metabolism, digestion, kidney and pancreas.  Acroterion   (talk)   14:44, 11 December 2022 (UTC)
 * Okay, so there is selectivity? (Insulin can metabolize sugar without metabolizing salt?) Or, is salt already separated out when the time the insulin meets the sugar? 67.165.185.178 (talk) 14:56, 11 December 2022 (UTC).
 * Salt is not metabolized, and it is not a source of energy. It is an essential nutrient. See sodium in biology.  Acroterion   (talk)   17:02, 11 December 2022 (UTC)
 * Since sugar is covalent, then there must be other things that are covalent like sugar, that insulin also metabolizes that might get in the way? 67.165.185.178 (talk) 17:37, 11 December 2022 (UTC).
 * Covalence is a property of bonds between atoms, not of compounds such as sugars. The kidney has a filtration system that can separate small ions from larger molecules; see . --Lambiam 19:45, 11 December 2022 (UTC)
 * The glucose is fact filtered into primary urine and then re-absorbed in renal tubules. Ruslik_ Zero 20:12, 11 December 2022 (UTC)
 * I'm looking at Digestion, which states sucrose is broken down by sucrase, and elsewhere it says it happens in the small intestine. Then, carbohydrate_metabolism says insulin and glucagon are the primary hormones involved in maintaining a steady level of glucose in the blood. I also see proteins are being digested in the stomach and small intestines. Now, I'm not seeing anything for salt, so Googling "how does the body digest salt" yields "Sodium is absorbed from the gastrointestinal tract, always bringing water along with it." So something from the intestines can go into the kidneys. And both salt and sugar make it to the small intestines. I'm wondering what is the next place for salt and sugar after the small intestines, directly into the kidneys? And then, kidneys filter out sugar into the renal tubules, salt does not? 67.165.185.178 (talk) 00:53, 12 December 2022 (UTC).
 * Sugar is a carbohydrate, which is digested. Salt is a mineral/essential nutrient, which is absorbed. One is metabolized, the other is not. There are two distinctly different processes involved,and bio;logically the two substances have drastically different roles and processes. You appear to be proceeding from false assumption of similarity.  Acroterion   (talk)   01:01, 12 December 2022 (UTC)
 * But in the small intestines, if you have salt and sugar in water, then the process to suck out salt 1st, from water, then there must be selectivity. Salt ions are smaller than sugar molecules so that should be some amazing selectivity. So it might be the salt are going through pores, like channels. 67.165.185.178 (talk) 02:43, 12 December 2022 (UTC).
 * Sodium absorption is complex and happens at multiple places along the digestive system. this briefly describes some of them.  -- Jayron 32 12:49, 12 December 2022 (UTC)

I like Lambiam and Ruslik's reference to the kidney articles. The link Jayron provided doesn't mention anything about kidneys, though it appears to me not much sugar is put into the kidneys. But Jayron's link has the professor's e-mail for questions, so I am e-mailing that. 67.165.185.178 (talk) 05:30, 16 December 2022 (UTC).

Sounds waves vs. light waves.
Can sound waves emit light and can light waves emit sound? Also, note that light-waves is a duality. The particle equivalent of light waves is photons, is there a particle-equivalent of sound waves? Thanks. 67.165.185.178 (talk) 14:46, 11 December 2022 (UTC).
 * Read Sound wave and Light wave. ←Baseball Bugs What's up, Doc? carrots→ 17:08, 11 December 2022 (UTC)
 * Read sonoluminescence, acousto-optics and phonon. Also not a good answer, but hopefully a little more to the point. --Wrongfilter (talk) 17:23, 11 December 2022 (UTC)
 * A 3rd question is are light waves and sound waves actually the same wave, then, can waves emit sound and light at the same time? (And what would you call that.). Unfortunately, those 2 articles don't seem to connect to each other. 67.165.185.178 (talk) 17:52, 11 December 2022 (UTC).
 * Maybe Bugs' articles are indeed more for you. Now it's unclear to me what you think light and sound waves actually are. --Wrongfilter (talk) 18:03, 11 December 2022 (UTC)
 * Yes. I never heard people associate sound waves with photons, for example. 67.165.185.178 (talk) 19:24, 11 December 2022 (UTC).
 * Light waves and sound waves are very definitely not manifestations of a common underlying physical phenomenon. Light waves are waves in the electromagnetic field. Sound waves are waves propagating in a fluid medium consisting of material particles such as molecules. In the vacuum of outer space, there is no sound, but light traverses it without problem. The speed of light is independent of the relative velocity of an observer, which cannot be said for sound waves (see Doppler effect). Even when abstracting from the physical context, these waves have different characteristics. Light waves are strictly transverse, while sound waves usually have a strong longitudinal component. In that respect, stadium waves are more like light waves. --Lambiam 19:34, 11 December 2022 (UTC)
 * Tiny correction: Sound waves propagate in all phases of matter, not just the fluid ones. See acoustics.  If they didn't, you wouldn't be able to hear them, as at least part of your hearing apparatus in your ear are solid bones (see ossicles).-- Jayron 32 12:42, 12 December 2022 (UTC)
 * A correction is needed there, Jayron. Sound waves propagate in any medium that has two key properties:  mass and elasticity.  Of course, there is practically nothing in this universe that doesn't have at least a small degree of elasticity.
 * The ear bones will have some elasticity, but in view of their small length compared to wavelength, it's negligible. But the transfer of sound energy via these bones is not by wave propagation.   It is merely by force transfer.  An analogy is that the transfer of energy from the transmitter tower to your radio is via a radio wave, but the transfer of energy from your radio's electronics to its' speaker is not a wave - it's just a forcing voltage.
 * Lambian also repeated a common misconception.  Sound waves (at ultra low frequency) DO propagate in outer space, because outer space is not a perfect vacuum.  There are a certain number of particles, atoms, electrons, etc that supply some minute mass and some elasticity via their (rare) collisions. Dionne Court (talk) Dionne Court (talk) 03:30, 18 December 2022 (UTC)
 * Hello user with IP 67.165.185.178 and welcome to the science reference desk, as a licenced amateur radio operator i can tell you that while they seem similar, light (electromagnetic) and sound waves are two different kinds of wave, sound waves are movements of air often arising from physical vibrations, and electromagnetic waves are a different form of energy that has a very wide spectrum so depending on the frequency, an EM wave could be a radio wave, heat, IR, or visible light, from what i know all EM radiation uses the same force carrier, photons, just like how sound propagates through air, so i wouldn't think there is such thing as a sound particle, physical vibrations are exactly that.
 * As for the conversion of light to sound, or vice versa, it's very possible at least with electronics and is commonly done, some music visualizers are simply light sources that are amplitude modulated by the music, or more advanced a spectrum analyzer, a spatial representation of the frequency spectrum, and the same is true the other way round, read about fibre optics and bells photophone, not only do we convert a form of invisible light into sound whenever we listen to a radio, but whatever modulation can be applied to a radio wave can also be applied to light waves, meaning that light, when modulated, can carry sounds and even data! OGWFP (talk) 21:36, 15 December 2022 (UTC)
 * There are no electromagnetic particles either.  For both electromagnetic waves (light, radio, etc) and sound waves, it has been discovered that, in some circumstances the mathematics of waves give the right answer, and in other circumstances the mathematics of particles gives the right answers.   It's just a human conceived way of describing how energy propagates - it does not mean that e.g., radio waves sometimes are waves but sometimes they magically turn into particles.
 * Dionne Court (talk) 10:27, 18 December 2022 (UTC)
 * Yes, sound waves can be considered as particles as well as waves, and doing so is sometimes useful.  Look up Wikipedia's article on phonons.  Dionne Court (talk) 03:33, 18 December 2022 (UTC)

Walrus's family
Wikipedia's walrus article says walruses are the only living member of their family, but dictionaries often define a walrus as being "of the seal family". Any 2 biological concepts it is important not to confuse?? Georgia guy (talk) 15:15, 11 December 2022 (UTC)


 * Our article says


 * Order:	Carnivora
 * Clade:	Pinnipedia
 * Family:	Odobenidae
 * Genus:	Odobenus
 * Species:	O. rosmarus


 * Pinnipedia include seals too. Dictionaries may be using the term 'family' more loosely. See the cladogram on the Pinniped article for the relationship. AndyTheGrump (talk) 15:31, 11 December 2022 (UTC)
 * When Illiger introduced the phylonym Pinnipedia, he defined it both as a family and a one-family order. The taxons of the usual taxonomic hierarchy correspond to cutting up the phylogenetic tree in layers. As far as I can see, there is no clear scientific criterion for where these cuts are made, and cladistics has multiplied the number of reasonable cutting points, obliterating any notion of comparing the cutting point levels in different trees in a sensible ranking system and leading to new taxon names such as suborder and superfamily. The traditional rank names for given clades, such as order, family (not a rank in the original taxonomy of Linnaeus) and genus, are based more on tradition than anything else. --Lambiam 18:37, 11 December 2022 (UTC)


 * It's rather arbitrary whether one calls the odobenidae a family and the pinnipedia a clade between order and family, or calls the pinnipedia a family and the odobenidae a clade between family and genus. Declaring a clade with a single species doesn't make a lot of sense, but there could be extinct relatives.
 * The whole idea of a ranked system made a lot of sense to Carl Linnaeus, who lived a hundred years before Charles Darwin, studied current animals and plants and noted that some were more similar to each other than others, and it still makes a lot of sense to those who study the organisms alive today. From an evolutionary point of view it makes no sense. What at one point in time is a genus of two closely related species may a hundred million years later have evolved into an entire order of hundreds of species. PiusImpavidus (talk) 10:07, 12 December 2022 (UTC)
 * To reiterate what PiusImpavidus said above in slightly different terms: You are rarely taught all the details of a complex subject in an introductory-level course like one has in high school or early college. Few people make it further into taxonomy than is taught in high school biology, and the classic hierarchy taught in such a class is extremely oversimplified and super-outdated.  The modern system of cladistics is much more useful, but also much more nuanced and complex, which is why most people don't learn it.  -- Jayron 32 12:36, 12 December 2022 (UTC)

What is added to wood, to prevent sunlight damage?
As in color change from sunlight. 2 answers I heard of are polyurethane and mineral oil. But, that strikes me as stuff that is easily wiped off, or does it get stuck inside the wood? 67.165.185.178 (talk) 20:50, 11 December 2022 (UTC).


 * Traditionally in Australia cedar homes are painted with used motor oil. It soaks in. Good thing we don't have bushfires Greglocock (talk) 21:58, 11 December 2022 (UTC)


 * While there is an article on Photodegradation, there is no section for wood. Search for wood photo-degradation yields results.  I personally have used catalyzed polyurethane and added an automotive UV inhibitor (probably HALS) for use on a wooden table; kinda expensive, but that was in the '70s, and it still looks like new. 136.56.52.157 (talk) 23:54, 11 December 2022 (UTC)
 * Wood preservation article might be helpful. 136.56.52.157 (talk) 00:21, 12 December 2022 (UTC)
 * There are wood preservation products, some use something called Trans-Oxide® which the manufacturer claims are manufactured to have needle-shaped particles that will not scatter light even when fully dispersed in the coating or vehicle. This makes them completely transparent and yet still able to impart high color tint strength, weather resistance and UV-barrier properties.  Exterior Danish Oil UV[|undefined includes UV inhibitor compounds [...that] absorb harmful ultraviolet light wavelengths and emit them harmlessly in the infrared range as heat.  They don't say what the "compounds" are, but probably includes metallic oxides. 136.56.52.157 (talk) 01:08, 12 December 2022 (UTC)
 * For not-too-expensive general use see: tung oil. 136.56.52.157 (talk) 01:17, 12 December 2022 (UTC)
 * I immediately thought of creosote which is cheap and widely used on wood in fences and other outdoor settings. Mike Turnbull (talk) 11:59, 12 December 2022 (UTC)
 * FYI: Creosote is banned in many jurisdictions, you'll have to put up with substitutes like CreoCote™. They claim to be as good as the original. Martin of Sheffield (talk) 15:41, 12 December 2022 (UTC)


 * Keeping wood from changing colors is often done via the use of wood sealants. The main options for wood are varnish and lacquer.  Generally three things can degrade the color of wood; being water, oxidation (air), and light.  Good sealants will stop water and air from fading the wood; and some will have materials that absorb UV light, which will additionally block most of the oxidative effects of sun.  -- Jayron <b style="color:#090">32</b> 14:20, 12 December 2022 (UTC)

Enteroctopus date: 1887 or 1889?
Most sources state the genus Enteroctopus was created by Alphonse Tremeau de Rochebrune and Jules François Mabille in 1889; however this is not entirely correct; It was published in 1889 in Mission scientifique du cap Horn, 1882-1883 but the very same book affirms it was created two years before, in 1887. So, what is the correct date? -- Carnby (talk) 21:25, 11 December 2022 (UTC)


 * Wasn't the genus created on the Fifth day of Creation? :) Generally, one goes by the publication date. --Lambiam 01:27, 12 December 2022 (UTC)


 * The 1889 article indeed gives the taxonomic authority of the binomial name Enteroctopus megalocyathus as Rochebrune & Mabille 1887. As a confusing side issue, nowadays we would write "Enteroctopus megalocyathus (Gould, 1852)" because Gould had come up with the species name already, but Rochebrune & Mabille here coined the generic name and they wrote themselves as the authors of the combination of the two names (a bit like the rules botanists still follow). The 1887 date is erroneous. It seems that their intention was to indicate that this name was new in their current work, and that they were both authors of this description. Presumably they expected their manuscript to be published in 1887, but in fact it appeared in 1897 1889 and nobody changed the date in the meantime. It is the actual date of publication that now counts. https://doi.org/10.11646/zootaxa.2723.1.2 probably explains more but is behind a paywall. Jmchutchinson (talk) 23:42, 13 December 2022 (UTC)