Wikipedia:Reference desk/Archives/Science/2021 July 19

Science desk
< July 18	<< Jun | July | Aug >>	July 20 >

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.

July 19

Covering bleeding wound with potato chip bag (or any non-absorbent material)

Are potato chip bags appropriate to cover a bleeding wound? I imagine that's better than nothing, but wouldn't an absorbent material be much more appropriate? I'd also wonder how clean a potato chip bag can be. Hands are a common vector of germs. --Bumptump (talk) 13:39, 19 July 2021 (UTC)

Presumably you're referencing this recent news story.[1] The details indicate the cop had someone get a bag of chips and some tape from a nearby store. Why a chip bag and not something better is hard to know for sure, but the cop probably went with something he could be sure they would have. It's also not like he picked it up off the street, so it was cleaner than it might have been. Sometimes when applying first aid, you have to go for expediency over optimal cleanliness. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:09, 19 July 2021 (UTC)

Clingfilm is a good alternative. The idea is to stem the bleeding and protect the wound from infection. Removing or disturbing the dressing, if it's absorbent, can cause more bleeding. Absorbent dressings are good if the wound has already been properly treated. nagualdesign 18:49, 19 July 2021 (UTC)

Per Bugs, appropriate compared to what? Are we talking "use the bag or let them bleed to death?" or are we talking "use the bag or use some sterile wound dressings"? The particulars of a situation and the choices available to the person at the time determine the appropriateness of their choices. With only a few seconds to make quick decisions, and with a lack of proper supplies, sometimes people make do. --Jayron32 18:51, 19 July 2021 (UTC)

I can't read the recent news story linked above, but there was a recent one about a polis using a crisp packet on a sucking wound. This is something I've been taught as a makeshift on First Aid courses. DuncanHill (talk) 20:22, 19 July 2021 (UTC)

Yes, same incident, an excellent writeup with details the OP should find interesting. The address given, 290 Lenox Avenue, is at about 125th Street in Manhattan, about 15 blocks north of Central Park and about 2 blocks east of the Apollo Theater. There are plenty of cafes in the area, so getting a bag of potato chips would have been easy - and it would be a good bet that it's not the first time a cop has had to use that trick. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:04, 19 July 2021 (UTC)

290 Lenox/Malcolm X is about 80 feet from a NYC delicatessen, those are almost guaranteed to have potato chip bags. Sagittarian Milky Way (talk) 04:26, 20 July 2021 (UTC)

• I'm no medic, but I took a 3 week life saver course in the Army years ago, and I know that non-porous bandages are a thing. One technique I remember was packing a wound with gauze and wrapping it in a non-porous bandage to cut down external bleeding (for when bleeding is "tactically ill-advised"), and another use was for sucking chest wounds, where I can be applied in such a way as to form a one-way valve. The main concerns are packing and keeping pressure on a wound to encourage clotting and pinch off any damaged arteries or veins. Note that this is all very much first-aid oriented. It may be very poor advice in an emergency room, and once again, I'm no expert. ᛗᛁᛟᛚᚾᛁᚱPants Tell me all about it. 21:53, 19 July 2021 (UTC)

  @MPants at work: What's that dry powder that you see soldiers pouring into bullet wounds in movies? Reading this it seems that keeping a wound moist is important (although that article is not really about emergency/temporary field dressings). Is it mainly to cause the hero to wince in pain, demonstrating how tough he is, in case taking a bullet and carrying on regardless wasn't enough? nagualdesign 22:31, 19 July 2021 (UTC)

  @Nagualdesign:: the powder is sulfonamide, see end of 3rd paragraph in this section: Sulfonamide_(medicine)#History.Bumptump (talk) 23:07, 19 July 2021 (UTC)

  This is correct, nagualdesign. It's also coagulant, to help stem bleeding. FWIW, we didn't have much in the way of little baggies of powder when I was in (AFAIK, that's a WWII-Vietnam era convention), but there were some for emergencies, and we had lots of different ready-made bandages impregnated with the stuff. ᛗᛁᛟᛚᚾᛁᚱPants Tell me all about it. 12:07, 20 July 2021 (UTC)

As I understand the story, the point of sealing the wound was not to keep the blood in, but to keep the air out.  --Lambiam 23:07, 19 July 2021 (UTC)

Por qué no los dos?--Jayron32 15:18, 20 July 2021 (UTC)

I thought the point of band-aids was to keep bacteria from coming in (as well as keeping blood from coming out), but since you mentioned air, does air bring in bacteria? I thought it was mostly bacteria on the nearby skin that would migrate in. 67.165.185.178 (talk) 06:32, 21 July 2021 (UTC).

Quoting our article Pneumothorax: "Any open chest wound should be covered with an airtight seal, as it carries a high risk of leading to tension pneumothorax." Here, "open chest wound" means a wound that creates a passageway allowing air to enter the pleural space. Tension pneumothorax is a life-threatening condition, as it may lead to cardiac arrest. Keeping bacteria out was under the circumstances not an immediate goal. If you run out of your burning house, it is a good idea not to leave the door open and allow new oxygen to enter. Closing the door may also keep mosquitoes out, but that is not the point.  --Lambiam 07:26, 22 July 2021 (UTC)

Ah, so probably the pressure of air to open-wounds is not suitable, pressure inside blood vessels is likely different? Hence the possibility of cardiac arrest. Body has some mechanism of fighting bacteria in the blood, but different pressures is a very different issue. 67.165.185.178 (talk) 10:47, 22 July 2021 (UTC).

Separate question, but Amoxicilin is a medicine that kills bacteria in the blood. But of course, it requires a doctor's prescription (or dentist). Are there any over-the-counter anti-biotic? That don't require a prescription? I'm also wondering if there are any cases where, a doctor's prescription and non-prescription are the same ingredient, only different concentrations. 67.165.185.178 (talk) 02:33, 20 July 2021 (UTC).

As a general rule, no: while there is some variability across localities, if you are living in an American or Commonwealth nation as your English implies, access to any medical-grade formulations of oral antibiotics designed and manufactured with human consumption in mind is going to be strictly controlled and regulated. If used in an amount or fashion inconsistent with proper medical supervision, all antibiotics have potential for not insignificant harm. Additionally, over use of antiobiotics in a completely unregulated environment would have massive implications for Antibiotic resistance and superbugs. Beyond that, we really cannot comment: your question here buts up against our rule against providing medical advice here. If you have a medical condition you believe would benefit from antibiotics, you should consult a licensed professional, and I recommend that advice if your inquiry is meant only for hypothetical future reference. Snow ^{let's rap} 03:55, 20 July 2021 (UTC)

The cited link is unavailable for European users, for some reason I don't understand. Can someone provide a link to whatever incident this was about? JIP | Talk 01:19, 21 July 2021 (UTC)

Yes, certain European newspaper websites block USA viewers and vice versa. It's to save bandwidth. But the url itself tells you a lot. 67.165.185.178 (talk) 01:24, 22 July 2021 (UTC).

@JIP: This American paper and this BBC link should work for you. DuncanHill (talk) 07:40, 22 July 2021 (UTC)

How gyroscopic forces helps us to keep upright when riding a bicycle

As far as I understand, when riding a bicycle the angular momentum of a spinning wheel creates a small, and not very useful, force that tends to keep the bike upright. This force is negligible, compared to the weight of the rider. Basically, riding upright depends of our ability to ride upright. Is that right? Do modern physic textbooks normally depict it this way? --Bumptump (talk) 13:45, 19 July 2021 (UTC)

Correct. The gyrostabilizing force is negligible. Balancing depends on the skill of the rider. nagualdesign 15:03, 19 July 2021 (UTC)

At the end of many stages in the Tour de France, for example, you'll see the winner peddling while holding his hands up in the air in celebration. Obviously he knows his bike well. But might that force described by the OP be a factor? ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:11, 19 July 2021 (UTC)

Much stronger than the gyroscopic effect is the effect caused by the geometry of the bike. The forward angle of the front wheel makes the bike steer into the direction it leans self correcting. However it does appear to be mostly the actions of the rider Opinion: How does a bike stay upright? Surprisingly, it’s all in the mind -- Q Chris (talk) 15:25, 19 July 2021 (UTC)

I don't think that the force is negligible. It provides information to the rider about the balance. Abductive (reasoning) 16:11, 19 July 2021 (UTC)

We have a fairly lengthy Bicycle and motorcycle dynamics article. DMacks (talk) 23:33, 19 July 2021 (UTC)

Slightly off-topic but readers may be interested. My nephew could ride a push bike the first time he got on one, because he'd previously had a balance bicycle. Apparently, learning to balance is a piece of cake when you don't have to think about pedalling, and pedalling is easy once you've learned how to balance. Highly recommended for anyone with young children. Of course, in my day we got scratches and bruises and we were thankful! nagualdesign 16:30, 19 July 2021 (UTC)

• I still wonder whether my secondary question is true: do modern physic textbooks get this right? Or is it already ingrained into physics that gyroscopic forces are what keeps the bike upright and authors just keep repeating this from other authors? A textbook in conceptual physics, Physics of Everyday Phenomena by Thomas Griffith, at least in the 6th edition, clearly believes otherwise. Bumptump (talk) 23:17, 19 July 2021 (UTC)

I don't read physics books, other than Feynman, but have a look at this http://www.phys.lsu.edu/faculty/gonzalez/Teaching/Phys7221/vol59no9p51_56.pdf Greglocock (talk) 23:37, 19 July 2021 (UTC)

It is not only the action of the rider. When an upright moving bicycle without rider starts to lean to one side, say for concreteness to the right (turning on a horizontal axis), the effect of the gyroscopic force on the front wheel makes it turn right (turning on a vertical axis). While the force is small, not much force is needed to make the wheel turn. This adds to the already substantial effect of the front wheel turning in these conditions because its axis of rotation is slanted with respect to the vertical (as mentioned above). The moving bicycle will then start a turn to the right, resulting in a centrifugal force that uprights the bicycle (if it has enough speed). The faster it goes, the stronger and quicker this automatic correction happens, so that a fast-moving riderless bicycle can travel quite some distance in an almost straight path.  --Lambiam 09:08, 20 July 2021 (UTC)

Gyroscopic effect and trail of the front wheel both contribute to the stability of the bicycle. You can put both in a mathematical model and solve it analytically and find that a bicycle is stable (in the sense that the real parts of the eigenvalues are negative, only at the right speed), but you can't really say which of the two effects causes this. And it's possible to make a bicycle with counterrotating flywheels (to eliminate the gyroscopic effect) or a reversly bent front fork (to eliminate the trail) and it may still be stable. Further, your average bicycle is unstable at high speeds, but only just. Deviations from equilibrium grow exponentially on a timescale on the order of one minute, so that's easy to correct by the rider. A bicycle at very low speed however can fall over in a second, making corrections by the cyclist much harder. PiusImpavidus (talk) 12:26, 20 July 2021 (UTC)

I think wheel size is important. I can ride my "normal" ten speed (26" wheels) no hands, but not my Brompton - it is far too unstable. Of course, this might be due to the frame geometry. --TrogWoolley (talk) 14:18, 20 July 2021 (UTC)

Definitely. Assuming the linear density of rim+tire is the same, the moment of inertia is proportional to the cube of the radius of the wheel, so larger wheels give much stronger gyroscopic effect. PiusImpavidus (talk) 08:58, 21 July 2021 (UTC)

If you stand on one foot while lifting the other high in the air, you might find it hard to keep your balance, but gently touching just one finger to the wall makes it much easier even though very little force is applied. It's similar with the angular momentum of the wheels turning. Balancing a bike without the wheels turning is called a track stand and it is harder, though doable with practice. 2601:648:8202:350:0:0:0:2B99 (talk) 01:17, 21 July 2021 (UTC)

Maps Amhara Region

Greetings, i was referenced here by a theahouse editor, can you help get me maps for the Amhara Region article, a region in Ethiopia?

• Köppen climate classification map of the region, and smaller subdivisions within the region if possible
• Topographic/altitude map
• Drainage map
• Agricultural maps of any kind

Thanks Dawit S Gondaria (talk) 17:16, 19 July 2021 (UTC)

Hey @Dawit S Gondaria: thanks for stopping by. I hope you get some more responses soon, but in the past I have had luck getting maps made at Wikipedia:Graphics Lab/Map workshop. There are several volunteer cartographers who help making maps. They may be able to help out. --Jayron32 18:48, 19 July 2021 (UTC)

@@Jayron32: Thank you so much, i will def try there! If anyone else has a better suggestion please do share Dawit S Gondaria (talk) 05:34, 20 July 2021 (UTC)