Wikipedia:Reference desk/Archives/Science/2021 September 7

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September 7

How can exercise burn stress?

From here, it says: When you exercise, you'll burn off some of your stress.

I know exercise burn calories but how it can burn stress too? Rizosome (talk) 01:41, 7 September 2021 (UTC)

Start with Exercise, note where it mentions "stress", and continue from there. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:36, 7 September 2021 (UTC)

STRESS RELIEF - The Role of Exercise in Stress Management describes the hormonal changes involved. The use of the term "burn" seems to be just journalese rather than an accurate description of the process. Alansplodge (talk) 21:06, 7 September 2021 (UTC)

Special relativity question

Suppose you have a train and its rest length is known. It runs on a track. On one side of the track and there are two light sources shining across the track, perpendicular to it. They are a known distance apart. On the other side of the track, the beams are reflected by mirrors into detectors that are at the position of a clock. The detectors record the time from the clock when they are receiving the light and when they are not. The apparatus is symmetrical with respect to the clock.

The train comes along the track at relativistic speed and the apparatus records the time each light beam is cut off and the time it resumes.

From the time that each beam is cut off and the known distance between the light beams, you can calculate the speed of the train. From that and the length of time that the light is cut off from either beam, you can calculate the length of the train.

Question: This calculated length of the train will show Lorentz contraction, right? Bubba73 ^{You talkin' to me?} 02:52, 7 September 2021 (UTC)

Is this the same as the ladder paradox? Robert McClenon (talk) 05:41, 7 September 2021 (UTC)

I don't think it is. The ladder paradox says "This apparent paradox results from the mistaken assumption of absolute simultaneity. " I don't see any use of absolute simultaneity. Bubba73 ^{You talkin' to me?} 06:22, 7 September 2021 (UTC)

Yes, the Lorentz contraction is a real physical, and measurable, phenomenon, not just a mathematical trick. If you were to measure the length of an object moving at close to the speed of light, it will be smaller in the direction of travel than if you measured it while stationary. This video does a good job of explaining it. --Jayron32 16:18, 7 September 2021 (UTC)

Also relevant, this most recent video from Minute Physics has a different experiment to measure length contraction. --Jayron32 16:20, 7 September 2021 (UTC)

Yes, that method will show Lorentz contraction of the train's length. --Amble (talk) 20:05, 7 September 2021 (UTC)

Resolved

That is what I thought, thank you. Bubba73 ^{You talkin' to me?} 21:30, 7 September 2021 (UTC)

Smartphone's screen smudges

Even though internet states that smartphone screens have an oleophobic coating, the finger smudges on the screen are still there (in my case it's Motorola E7i, but I guess any other smartphone has the same). Is it because the oleophobic coating is too thin to prevent smudges or some other reason? More generally, is it possible to produce a smudge-resistant touch screen? 212.180.235.46 (talk) 19:46, 7 September 2021 (UTC)

A thicker coating layer will not reduce the amount of sebum transferred to the screen. Such transfer takes place at the outer surface of that layer. No coating can guarantee a full 100% protection against smudge attacks, but matte screen protectors make such attacks less easy. I did not readily see information about the affinity to oil or lack thereof of the Motorola E7i screen, but ads offering oleophobic screen protectors for this model abound.  --Lambiam 07:10, 8 September 2021 (UTC)

Removing ticks?

Just for future reference because i forgot. Are you supposed to twist the tick clockwise or anti clockwise to get it out? 146.200.107.70 (talk) 23:10, 7 September 2021 (UTC)

Neither. Here's how.[1] ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:54, 8 September 2021 (UTC)

Are you ready for a journey through the tick-removal sources? No? Well, the short answer is that there is no twisting direction (i.e. the ticks are not screw-mouthed), but depending on the tool used you should or should not twist (do not twist tweezers, do twist if it is some sort of grooved tool). The reference in bold below is short and not very hard to read.

But if you are up for it... I started by looking up public health services. Hmm, that’s funny. The US CDC linked above does say not to rotate the tick. The UK NHS does not say anything about rotation, whether to perform it or avoid it. In French, I found this from the NHS equivalent which says to twist, but not which way - Pour ne pas casser l’appareil buccal (le rostre), faites un mouvement circulaire. Ce mouvement de traction-rotation, réalisé perpendiculairement à la peau, permet de retirer la (ou les) tique(s) sans leur arracher la tête. - To avoid breaking the mouth part, make a circular motion. The twist-pull motion should be made perpendicular to the skin to remove the tick with breaking off its head.; as well as this prevention poster indicating a counter-clockwise turn (image 5) but I would not be confident the artist consulted a doctor to draw it.

I found this (Stackexchange answer, but it looks somewhat detailed) which claims that the difference is in the tool used: tweezers should not be twisted, but tick removal tools should be. It also claims that ticks are not screw-headed.

At that point I started wondering if maybe some species are screw-headed and some are not. Diving through Google Scholar, I could not find any reliable source that addresses the question head-on (no pun intended), but I did find these lecture notes which mention all the varieties of tick and how to identify them and collect them in the wild etc. do not mention screw-headedness anywhere. One might reasonably assume that such a key information of morphology would have been present in such a document, and its absence therefore strongly suggests that the belief in the screw-headedness of ticks is a urban legend.

Wait, did I say urban legend? A quick check of Snopes turns up a page that is not very interesting but that does link to a scientific review.

Finally, I got to what is likely to be the last word on the subject: Removal of ticks: review of the literature. The journal Eurosurveillance seems legit from its wp page. I can hardly summarize what they say more than they already do

Now for my interpretation: I would assume that from a mechanical point of view is that twisting is dangerous with tweezers, because you cannot reliably rotate parallel to the skin, and off-axis rotation would cause strong mechanical stress on the barbed things attaching the tick and break the head off. However, if you do have a tool that allows twisting with a safe orientation, then it might make the barbed things fold around; you still have to pull it off, but it eases the removal compared to a straight-pull method. ("Might", because it is based on a video demo by a company that sells the stuff to do it; the demo seems believable but I have no idea if the tick and skin model they use has realistic mechanical properties.) However, the screw-mouthiness is an urban legend (which I believed in at the start of this hunt, having "learnt" it from a vet from a rural area). Tigraan^{Click here for my talk page ("private" contact)} 10:26, 13 September 2021 (UTC)