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June 20

Is the dominant hand more, equal or less sensitive?

Which hand is more sensitive for physical feeling, is it is the dominant hand (which is the right side for most of the people) or non-dominant hand? In other words, I can ask if there's a correlation between the dominance of the hand to its quality of sensation or not? --ThePupil (talk) 01:11, 20 June 2020 (UTC)[reply]

What does your own experience tell you? ←Baseball Bugs ^{What's up, Doc?} carrots→ 08:18, 20 June 2020 (UTC)[reply]

A person's "own experience" would be, at best, a subjective anecdote. Do you consider that appropriate for a science reference desk? 2A01:E34:EF5E:4640:2C28:10B6:13A1:E56 (talk) 09:48, 20 June 2020 (UTC)[reply]

It's a useful starting point. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:36, 20 June 2020 (UTC)[reply]

Based on my own experienced, I really can't decide which is more sensitive. Therefore, I'd rely on research that tried to answer to question scientifically.

I also thought of it as a starting point, but then decided it was useless: perhaps the truth is that the left hand is usually more sensitive regardless of the person's handedness. Wedding rings are worn on the left hand for reasons sort of related to that (the left hand is closer to the heart and the vena amoris supposedly ran from the left ring finger to the heart). Checking one's own experience would suggest to left handed people that the dominant hand is more sensitive; and to right-handed people, the opposite. You need larger N of both populations. 2602:24A:DE47:BB20:50DE:F402:42A6:A17D (talk) 02:15, 21 June 2020 (UTC)[reply]

You could try hitting your left thumb with a hammer, then your right thumb, and see which one hurts more. (Like the stereotype of hitting a thumb while nailing something.[1]) ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:51, 22 June 2020 (UTC)[reply]

This is a (not peer-reviewed) report on a 2014 California State Science Fair project that found a slight but significantly higher touch sensitivity in the dominant hand. Another study appears to show that right-handed males have lower pain sensitivity in their dominant hands, while no difference was found for left-handed males or females. So the answer may depend on (a) the kind of sensitivity; (b) the gender of the subject; (c) the handedness of the subject. --Lambiam 08:24, 20 June 2020 (UTC)[reply]

Thank you. I'm more interested in the touch sense. I wish I found more serious studies about it. --ThePupil (talk) 19:09, 20 June 2020 (UTC)[reply]

Why would either hand be more sensitive? The assumption in the question is that sensitivity would vary with dominance. Would this assumption be based on anything? Bus stop (talk) 02:20, 21 June 2020 (UTC)[reply]

Are we not allowed to ask the question if there is a correlation without a prior reasonable basis for assuming that there is one? Would the opposite assumption (the null hypothesis) that sensitivity does not vary with dominance be based on anything? --Lambiam 13:51, 21 June 2020 (UTC)[reply]

My mistake. We are allowed to ask the question, Lambiam. But let me raise a separate question—what is meant by "sensitivity"? I think we have to define this. Bus stop (talk) 15:24, 21 June 2020 (UTC)[reply]

My reply above already drew attention to the fact that there are different kinds of sensitivity, to which the OP replied by stating they were more interested in the touch sense. As to the sense of touch, usually given in term of the pressure threshold at which touching is detected, even there we should distinguish between sensitivity to pressure ("crude touch"), and the ability to localize the spot being touched ("fine touch"), as determined by two-point discrimination tests. The first study I linked to above was mostly about crude touch. This study is about fine touch; it found that "considerable differences do exist in normative values for Two Point Discrimination ability in the dominant and non dominant hand in a sample of normal healthy males and females". --Lambiam 20:47, 21 June 2020 (UTC)[reply]

Would not "sensitivity" also cover ground relating to Fine motor skills? Bus stop (talk) 21:01, 21 June 2020 (UTC)[reply]

Unless you can specify what you are asking about, "sensitivity" to what? (temperature?, pressure?, roughness?, pain?), the question doesn't even have a potential answer. If you do specify, the answer may still be unknown. --Khajidha (talk) 23:17, 21 June 2020 (UTC)[reply]

Déjà vu: water cavitation and X-rays

I've heard recently from someone that they have it on good authority (haha) that cavitation in water seems to produce X-ray radiation, and that the mechanics of this are entirely a mystery to science. The thing is, I can vaguely remember hearing from a definitely non-kooky source about some real connection between cavitation and EM radiation. Maybe cavitation has influence on like Cherenkov radiation? Or is it some kind of problem for nuclear reactors or something? Does any of this sound at all familiar to you guys? 93.136.75.126 (talk) 14:19, 20 June 2020 (UTC)[reply]

See Sonoluminescence which happens to radiate blackbody radiation and appears to not yet be demonstrated to be hot enough, ~millions of degrees, to produce x-rays. --Modocc (talk) 15:43, 20 June 2020 (UTC)[reply]

Yeah that sounds like it, thanks Modocc. Knew it was something legitimate. X-rays and specificity to H₂O were probably added through pseudoscience's usual Chinese whispers. 93.136.75.126 (talk) 15:59, 20 June 2020 (UTC)[reply]

There’s also peeling off a piece of tape to produce X-rays.[2] DMacks (talk) 17:28, 20 June 2020 (UTC)[reply]

Aa yes that rings a bell too, many thanks! 93.136.75.126 (talk) 20:24, 20 June 2020 (UTC)[reply]

Not trolling, but Chinese whispers? — Preceding unsigned comment added by 216.15.48.37 (talk) 00:44, 24 June 2020 (UTC)[reply]

Jupiter's Temperature

What is the temperature of Jupiter's surface and how does it compare to the temperature of its core? Thank you! 47.28.215.122 (talk) 21:14, 20 June 2020 (UTC)[reply]

Jupiter, being a gas giant doesn't really have a "surface"; however:

Scientists therefore define the surface as the atmospheric layer in which the pressure is the same as on the surface of the Earth. At this depth, the temperature is uniform at minus 145 degrees Celsius (minus 234 degrees Fahrenheit), reports Space.com.

And:

Scientists estimate the core temperature of Jupiter to be about 24,000 degrees Celsius (43,000 degrees Fahrenheit), which is hotter than the surface of the sun.

Chris Deziel (April 24, 2017). "What Is the Average Temperature of Jupiter?". Sciencing. —107.15.157.44 (talk) 23:25, 20 June 2020 (UTC)[reply]

Interesting speculations about Jupiter:

--Guy Macon (talk) 06:39, 21 June 2020 (UTC)[reply]

Land bridge dispute?

The article on the British Isles says:

Whether or not there was a land bridge between Great Britain and Ireland at this time is somewhat disputed, though there was certainly a single ice sheet covering the entire sea.

But the article on Beringia says:

Around 14,000 years ago....the British Isles became an extension of continental Europe via the dry beds of the English Channel and North Sea

Both are unsourced. Given the evidence, however, is this really disputed? Viriditas (talk) 21:39, 20 June 2020 (UTC)[reply]

I somewhat agree that the wording in the geography section is problematic, not least because it appears to contradict the wording in the flora and fauna section "The only window when this could have occurred was between the end of the last Ice Age (about 12,000 years ago) and when the land bridge connecting the two islands was flooded by sea (about 8,000 years ago)." which appears to treat the existence of a land bridge as a given. Further the meaning of "at this time" is unclear, the preceding sentence refers to the period between the end of the Last Glacial Period, and 4000-5000 years ago, so I guess it's probably referring to this period only (but the entire length), but I think it needs more clarity even if it is true. I don't know much about historical geology of the area but my read of Doggerland, is that it is well accepted there was a land bridge, although precisely when and how it finally came to an end is disputed. Nil Einne (talk) 23:48, 20 June 2020 (UTC)[reply]

The abstract of a 1995 paper by Kurt Lambeck entitled "Late Devensian and Holocene shorelines of the British Isles and North Sea from models of glacio-hydro-isostatic rebound" states: "The model predictions for the Irish and Celtic Seas also suggest a complex behaviour, with the formation of a wide land bridge between about 20 000 and 13 000 years ago. The model also suggests that as long as the Scottish ice extended across the northern Irish Sea, until about 14 000 years ago, there would have been a large freshwater periglacial lake located further south. Both the predicted sea-level height-age relations and the shoreline positions are consistent with a large body of observational evidence but some discrepancies occur, particularly in northern Scotland and Ireland where the ice heights may have been somewhat greater than assumed in the model." This formulation implies that there is no direct conclusive evidence either way, but at best a tentative conclusion based on the available evidence interpreted in light of a sophisticated model. I think that the dates given for the predicted land bridge mean that the bridge had disappeared 13 000 years ago. I have not investigated if there has been subsequent discussion of this paper in which scientists question its conclusions. --Lambiam 11:04, 21 June 2020 (UTC)[reply]

I'm not seeing a contradiction in the quoted sentences. The first is about a connection between the two islands (GB and Ireland) and the second is about those islands being connected to the mainland. --Khajidha (talk) 15:23, 21 June 2020 (UTC)[reply]

You're right about the Doggerland bit I mentioned and Beringia by the OP, I missed that apologies. But both the quote in the geology section and in the flora and fauna section seem to be clearly referring to the land bridge between GB and Ireland yet one says it's disputed, the other treats it as if it existed at some stage during the defined period until flooded 8000 years ago. Nil Einne (talk) 01:25, 22 June 2020 (UTC)[reply]

Vehicle fuel consumption: level road versus road with gradients

Is it always the case that a motor vehicle travelling along a level road will use less fuel than an identical vehicle travelling an identical distance on a road with gradients, even if the latter vehicle is able to gain sufficient height over a short distance that it can freewheel for much of the way? PaleCloudedWhite (talk) 21:48, 20 June 2020 (UTC)[reply]

A few reasons in favor: firstly, (assuming spherical cows) we can subtract horizontal motion and end up with work being done to elevate the vehicle uphill and lower it downhill into the gravity well. Since no work can be perfectly efficient, we must input net energy to complete the lowering and descending sequence. Secondly, since a straight line is notably the shortest curve between two points in space, by driving up and down the hill we pass a longer distance and waste more fuel on tire friction, which is the top energy expenditure at city driving speeds. Thirdly, on long downhill stretches the vehicle can pick up enough speed freewheeling to run into extra friction from air drag.

On the other hand, the hill route might have advantages like fewer turns or a mountain providing a windbreak, or the vehicle (or the driver) might be in some unexpected way be much better suited to climbing and descending than driving on a flat road. For example, many cars have a low fuel consumption around 30-40 km/h and again around 90-130 km/h with a spike in-between. Also the truly shortest route between two points on Earth doesn't follow the surface of equal gravitational potential. In fact it digs slightly into Earth as a trench. Driving thru such a trench could might actually be preferable to driving along the surface curvature at some distances. There's also the copout that the flat route might have a terrible pavement. Slipping in mud and braking to dodge potholes is also a waste of fuel.

I can think of one major problem with most people's driving styles on a road with gradients: imagine that tire friction = 0 and the car is driving 130 km/h and encounters a large plateau. Climbing up the plateau gains gravitational potential energy and accordingly costs kinetic energy, so after the climb the car continues on the plateau at say 80 km/h. At the end of the plateau the car descends and if the climb and descent were perpetuum-mobile 100% efficient, the car is back up at 130 km/h. What do most people do? They've kept the cruise control at 130 km/h all along. 93.136.75.126 (talk) 02:05, 21 June 2020 (UTC)[reply]

I suspect the answer is ... it depends. Mileage Marathon cars use short bursts of wide open throttle, followed by coasting. An appropriate sequence of hills could be used to approximate this driving schedule. One significant aspect is whether you are allowed to switch your engine off when coasting, or declutch. Greglocock (talk) 03:52, 21 June 2020 (UTC)[reply]

The contributions above show sufficiently that if "always" is taken literally, the answer to the original question is "no, not always". Instead of covering "an identical distance", which is a bit ambiguous, let both roads go from the same point A to the same point B. The conditions can perhaps be refined a bit to create a more idealized problem. First, assume a uniform field of gravity, one in which the curvature of the Earth is negligible. Second, assume there is no wind. Third, assume the level road goes straight all the way. Fourth, assume for either route the road has the best possible surface for driving on, and the (varying) speed at which the vehicle is driven along the route is the most fuel-efficient one for that route. I suspect that with these additional stipulations the answer becomes "yes" – but I do not see a ready way to establish this without an abstract theory of fuel consumption as a function of many factors, introducing further restrictions on the possibilities (and what about hybrid car models?). If the answer is still "no", perhaps future roads can be made to go up and down to save on fuel :). --Lambiam 09:56, 21 June 2020 (UTC)[reply]

"Thirdly, on long downhill stretches the vehicle can pick up enough speed freewheeling to run into extra friction from air drag." Isn't this irrelevant?Hayttom (talk) 17:52, 23 June 2020 (UTC)[reply]