Wikipedia:Reference desk/Archives/Science/2022 June 23

Science desk
< June 22	<< May | June | Jul >>	June 24 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is a transcluded archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

June 23

Redox Double Displacement reaction

A double displacement reaction can never be a redox reaction. Is this true only for the Modern Concept (electronic concept) or also for the old concept(addition and reduction of Oxygen and hydrogen)?--ExclusiveEditor _{Notify Me!} 13:13, 23 June 2022 (UTC)

As the article salt metathesis reaction makes clear, this sort of reaction is usually ${\ce {AB + CD -> AD + CB}}$, driven by the insolubility of one of the products. These are not redox reactions as typically no change in valency of the individual components occurs. I would hesitate to say they could "never" involve a redox change, for example if one of the products AD and CB were very susceptible to, say, oxidation by air in an experiment where air had not been excluded. Mike Turnbull (talk) 16:33, 24 June 2022 (UTC)

If the bonds are all ionic, then there's clearly no redox because the four entities (A, B, C, D) each are unchanged. If we get into covalents though (which, oddly, salt metathesis reaction includes in-scope), then redox is certainly possible (simple example is Halogenation#Free radical halogenation). User talk:ExclusiveEditor, could you give us the source of this "can never" claim, so we can see its context/scope and academic level? DMacks (talk) 17:23, 24 June 2022 (UTC)

@DMacks: Actually, I heard that somewhere, still a quick search on the internet provides this source- Resource1 and many answers to this Quora query say no - Qoura1. --ExclusiveEditor _{Notify Me!} 13:34, 25 June 2022 (UTC)

Those seem to fit well with the "ionic"(-like) concept. DMacks (talk) 14:01, 26 June 2022 (UTC)

Testicular motion

I got home from work about an hour ago. It's been a really hot day so to cool down I took my clothes off and reclined on my bed. Although I was motionless apart from my breathing, I noticed that my testicles were constantly moving back and forth around every 20~30 seconds. It's not something I've ever noticed before. I'm aware that testicles obviously move, and I've just been reading our article about the cremasteric reflex, but I didn't realize just how much they move. Or rather, I wasn't aware that they moved continuously. What's going on here? Is it just because I'm a bit too hot? nagualdesign 15:05, 23 June 2022 (UTC)

Yes. Your genetic survival depends on the temperature of your testicles. Abductive (reasoning) 21:30, 23 June 2022 (UTC)

I'm aware of that, but why the continuous motion? I would have thought that they'd reach some sort of equilibrium. Is it easier to reach equilibrium at a lower temperature, or do they always move? I'm in my 40s and have never witnessed it before. nagualdesign 22:16, 23 June 2022 (UTC)

They are drawn in towards the body to get warmer, released outwards to cool. Presumably they are also in motion to take advantage of cooler areas of the scrotum where air circulation (and sweating, in animals that sweat) has allowed more cooling. Since the body does not know exactly where these cool areas are, moving them around decreases the odds of one testicle or one area of a testicle will overheat and kill cells. I recall hearing that once the scrotum has relaxed entirely in the heat, the movement mechanism (which has a name, I think) is engaged. Abductive (reasoning) 23:32, 23 June 2022 (UTC)

See Cremaster muscle (which is the "movement mechanism") and Testicle#Temperature regulation and responses. Martin of Sheffield (talk) 06:13, 24 June 2022 (UTC)

Thank you for the responses but none of them tell me anything I didn't already know. Everyone knows that they move up when it's cold and down when it's warm. What I'm asking is do they always move up and down continuously? Abductive gave the most interesting answer but it seems like mostly supposition. If anyone can provide links to more concrete information that would be great. It might even be worth adding some information to Cremaster muscle and Cremasteric reflex if any is forthcoming.^{Pun intended} nagualdesign 21:58, 24 June 2022 (UTC)

...Perhaps I should add that about 20 years ago I found a lump on my left testicle. I went to see a doctor and she squeezed it, which hurt like a motherfucker, and dismissed it as a cyst. I then suffered from severe inguinal pain for almost a year and struggled to walk (tip: do NOT see a female doctor for a men's problem!) until I had an ultrasound scan, which revealed that it was actually a varicocele, and was told how to flush out any "melancholic blood" to stop the pain. A few years earlier my brother had also suffered from epididymal orchitis (extremely painful!), so he and I are keenly aware of testicular physiology and have even seen the inside of our respective testes. All this is to say that I'm looking for information that's perhaps less commonly known. I've tried googling several things but all you get is the same information that should be very obvious to any adult male. nagualdesign 22:17, 24 June 2022 (UTC)

Asteroid speed variation in it's hyperbolic trajectory from infinity and passing near the sun

I find a lot of article describing asteroid hyperbolic trajectory, comming from infinity and passing near the sun, in a two body problem. But nothing describing it's speed variation from speed Vi (at infinity and not relativistic) to it's maximum speed Vr when it is closest to the sun, and again to it's original speed at infinity. Malypaet (talk) 21:31, 23 June 2022 (UTC)

I think you'll find Mr Kepler figured that out for you. Greglocock (talk) 23:23, 23 June 2022 (UTC)

Its speed and trajectory depend on its initial speed and location. Bubba73 ^{You talkin' to me?} 02:42, 24 June 2022 (UTC)

Let $E_{\text{k}}$ and $U$ denote, respectively, the kinetic energy and the gravitational energy of the body. Their sum, $E_{\text{k}}+U,$ is constant. Let $G$ denote the gravitational constant and $M_{\odot }$ the solar mass. The variable $R$ stands for distance of the body from the sun, and $v_{R}$ for the magnitude of its velocity at that distance. Dividing $E_{\text{k}}+U$ by the mass of the body, we have:

${\frac {1}{2}}v_{R}^{2}-{\frac {GM_{\odot }}{R}}=C,$

in which $C$ is a constant, not varying with $R.$ Plugging in $R=\infty ,$ we find $C={\frac {1}{2}}v_{\infty }^{2},$ and so:

$v_{R}=\left(v_{\infty }^{2}+2{\frac {GM_{\odot }}{R}}\right)^{\frac {1}{2}}.$

 --Lambiam 11:10, 24 June 2022 (UTC)

Or you can write

$v_{R}=\left(v_{\infty }^{2}+v_{esc}^{2}\right)^{\frac {1}{2}}.$

where $v_{esc}$ is the escape velocity at the distance $R$. Ruslik_Zero 20:18, 24 June 2022 (UTC)