Wikipedia:Reference desk/Archives/Science/2024 October 29

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October 29

Which ones (if any) of the following seven bodies, have both a [mechanical] equilibrium and a varying quadrupole moment?

Seven bodies.

HOTmag (talk) 07:56, 29 October 2024 (UTC)

The four objects in the middle appear to be in equilibrium and have a constant quadrupole moment. The rod in the upper right has varying quadrupole moment, but is in equilibrium (apart from the torque resulting from the emission of gravitational waves). The rod on the lower right has a varying quadrupole moment and is not in mechanical equilibrium, as its centre of mass moves in a circle. I can't be sure about the teapot. It looks like its quadrupole moment varies, its centre of mass moves, so there's a net force, and it doesn't spin on a principal axis, so there's a net torque. PiusImpavidus (talk) 09:16, 29 October 2024 (UTC)

Thx. By equilibrium I meant mechanical equilibrium, i e. both of forces and of torques (Sorry for not adding this from the beginning). So is your answer still valid after adding this addition? HOTmag (talk) 10:34, 29 October 2024 (UTC)

Yes, I already assumed that was what you meant by mechanical equilibrium. PiusImpavidus (talk) 13:53, 29 October 2024 (UTC)

Thx. HOTmag (talk) 15:45, 29 October 2024 (UTC)

Aardvark cucumbers and Madagascar

in the article on aardvarks habitat and range it states that they are not found in Madagascar

the article on the aardvark cucumber states that it can be found in Madagascar

Yet. both articles make it clear that the aardvark is necessary for the cucumber to grow and thrive

So my question is, what animal assists the cucumber in madagascar where there are no aardvarks?140.147.160.225 (talk) 12:53, 29 October 2024 (UTC)

I find this interesting. I've found multiple sources for related information. The aardvark cucumber is only eaten by aardvarks (many sources state that, but surely SOMETHING will also eat it). Humans do not eat aardvark cucumbers, and therefore do not farm them. There are no aardvarks on Madagascar. A closely related animal was last noted in 1895. It is assumed extinct. The only source that claims there are aardvark cucumbers on Madagascar is Wikipedia. Every website I found that made that claim was simply a copy of the Wikipedia page. The claim on Wikipedia is unsourced, so it is most likely not true. Unless someone can find a reliable resource that is not a copy of the Wikipedia article, I suggest removing Madagascar from the aardvark cucumber article. 12.116.29.106 (talk) 13:51, 29 October 2024 (UTC)

Thanks 12.116! I have removed Madagascar from the cucumber article and left an edit summary explaining140.147.160.225 (talk) 16:46, 29 October 2024 (UTC)

Because resources are very hard to find, I sent emails to a few organizations to ask for help including some nature reserves on Madagascar, a few large botanical gardens with African collections, and a few botanist instructors that I know. If we are lucky, one of them will respond. 12.116.29.106 (talk) 16:51, 29 October 2024 (UTC)

Why aren't bone balls big enough that they can't leave the socket without cracking bone?

Is this kind of ball-and-socket joint a local fitness maximum ? Sagittarian Milky Way (talk) 19:25, 29 October 2024 (UTC)

Isn't the question its own answer? Abductive (reasoning) 01:20, 30 October 2024 (UTC)

Yeah, you're probably better off with a dislocated limb that might pop back in place, than a nasty fracture to a precise structure. In fact there's probably a name for this concept in engineering, something like redundancy (engineering). Except not that. Fault tolerance? Fail-safe? That general conceptual area. Apple's MagSafe system comes to mind.  Card Zero  (talk) 06:07, 30 October 2024 (UTC)

There is also the concept of graceful degredation^[1] (Wot? No article??) graceful degradation, which seems to have been engineered by evolution into the functioning of the brain.  --Lambiam 12:10, 30 October 2024 (UTC)

There is a long-standing redirect from graceful degradation [sic] to fault tolerance. Mike Turnbull (talk) 16:22, 30 October 2024 (UTC)

Wouldn't the possibility of "overshooting the mark" and having the head become to big to move within the cavity also be relevant? --User:Khajidha (talk) (contributions) 12:20, 30 October 2024 (UTC)

It's been on Wikipedia over 241 months just not a similar-sounding typo of it. Sagittarian Milky Way (talk) 15:47, 30 October 2024 (UTC)

A generic engineering term is fail-safe: a feature of a design whose purpose is to reduce harm in the event of a failure of the design. An example are pressure relief valves; gradual release of possibly noxious gases is better than a catastrophic blowup.  --Lambiam 12:32, 30 October 2024 (UTC)

The incidental Cam out feature of Phillips screwdrivers similarly reduces damage when stress exceeds a normal range. Philvoids (talk) 14:09, 30 October 2024 (UTC)

In German we have the wonderful term Sollbruchstelle ("predetermined breaking point"), describing a predetermined failure mode with (hopefully) minimal collateral damage. --Stephan Schulz (talk) 22:17, 7 November 2024 (UTC)

It would give you either a thin connection between the ball and the rest of the bone it belongs to, or a limited range of motion. PiusImpavidus (talk) 16:07, 30 October 2024 (UTC)

Is the shoulder socket even over a full hemisphere? Sagittarian Milky Way (talk) 17:50, 30 October 2024 (UTC)

Nowhere near – see the illustrations in Scapula, particularly Figure 1, and in Glenoid fossa, which is the actual 'socket'. {The poster formerly known as 87.81.230.195} 94.6.86.81 (talk) 23:09, 30 October 2024 (UTC)

Why'd they draw a minimalist mechanical ball joint next to an anatomical one and compare them to mechanical ball joints when there's so many more accurate possible names like ball-and-wok joint or ball-and-hollow joint or ball-and-bowl joint or ball-and-depression joint or ball-and-crater joint? Sagittarian Milky Way (talk) 15:06, 31 October 2024 (UTC)

Anatomists have traditionally used the 'ball and socket' terminology for a long time, perhaps because the term is well established and familiar to most people even outside of anatomy, whereas the others you mention are not in general use (I assume you just made them up). There is no implication that the socket has to be at least a (concave) hemisphere – see for example Ground glass joint#Ball-and-socket joints.

Note that the linked article mentions the condition you specified in your query title: "An enarthrosis is a special kind of spheroidal joint in which the socket covers the sphere beyond its equator", and the linked reference notes that the (human) hip joint is an example of this. {The poster formerly known as 87.81.230.195} 94.6.86.81 (talk) 15:32, 31 October 2024 (UTC)

How can hips sometimes pop out without any bone fractures? Is it mostly cause everything's at least slightly compressible even bone and cartilage or is it mostly abrasion from being shoved through a slightly too small hole or is it that the ball would only need help to fit if it filled the socket to the exclusion of the liquid joint lubricant? Sagittarian Milky Way (talk) 18:19, 31 October 2024 (UTC)

Because, as you suggest, not just bone is involved. There are (in a healthy joint) layers of cartilage and other tissues between the bone of the ball and the wall and rim of the socket, which can be somewhat (painfully) compressed, and bone can be slightly flexible. Also, the socket is only just more than a hemisphere (and individuals will differ a little). {The poster formerly known as 87.81.230.195} 94.6.86.81 (talk) 19:28, 31 October 2024 (UTC)

That the ball normally maintains contact with the socket is due to the strength of the somewhat elastic joint capsule keeping them together. But the application of too large a force can distend the membranes of this joint capsule enough for the ball to dislocate (jump out of its usual seat).  --Lambiam 20:19, 31 October 2024 (UTC)