Wikipedia:Reference desk/Archives/Science/2018 July 10

= July 10 =

Surviving a firenado
Could a person survive getting sucked into a “firenado”? The question was inspired when I watch Into the Storm where a man got sucked into a firenado and die. Planet Star  00:40, 10 July 2018 (UTC)


 * Responders who want to tackle this one might want to peruse Into the Storm (2014 film) and Fire whirl. People occasionally survive all manner of seemingly unsurvivable events, but I'd think that being drawn into a tornado of essentially turbocharged gasses burning at 1,000°C would be quite hard to survive, as even if the victim was thrown clear quite quickly, a breath or two would likely cause fatal lung damage. I haven't myself been able to find any authoritative references specific to 'firenadoes', however. {The poster formerly known as 87.81.230.195} 90.212.98.167 (talk) 02:11, 10 July 2018 (UTC)

Why are the Great Plains of North America not considered to be a system of piedmont plateaus?
Or thought of as one.... A plateau is a high plain. Piedmont plateaus are plateaus that are bordered on one side by mountains and on the other by a body of water or a plain as is the case with the Piedmont Plateau east of the Appalachian mountains and west of the Atlantic Plain, and the Appalachian Plateau on the west of these mountains and east of the Central Plains. That all sounds like the Great Plains. The high plains of the Great Plains are west of the lower Central Plains and east of the Rocky Mountains. The Great Plains reach heights higher than 6000 ft above sea level in some areas. For example, Colorado Springs is around 6035 ft above sea level and Cheyenne, Wyoming is around 6062 ft in elevation. The Continental Divide is around 11000 ft in elevation, but the peaks of the Rocky Mountains can reach above 13000 to 14000 ft in elevation. One can see the the land rising as one approaches the Great Plains in some areas. What characteristics do the Great Plains lack from a piedmont plateau or is it actually a system of piedmont plateaus? Willminator (talk) 03:35, 10 July 2018 (UTC)
 * Have you read Great Plains? ←Baseball Bugs What's up, Doc? carrots→ 04:54, 10 July 2018 (UTC)
 * It may be true that you can see the land rising as you approach them in some places but the part I crossed was very flat. It's a mile high drop but hundreds of miles wide and some elevation ranges of that mile are surely steeper than others. The Plains are mostly volcanic ash deposits from the Rocky Mountains erupting since before the range was the height of the Himalayas or Andes, the further east the less ash and the closer to sea level. Sagittarian Milky Way (talk) 05:30, 10 July 2018 (UTC)
 * "Mostly volcanic ash..."? That isn't how I learned my geology.  The U.S. Geological Survey summary of the interior plains describes a great inland sea from which sediments accumulated and compressed.
 * Nimur (talk) 11:35, 10 July 2018 (UTC)
 * Huh, you are correct. How far west did the sea ever get? Sagittarian Milky Way (talk) 12:57, 10 July 2018 (UTC)
 * Well, that's a complicated question because over geological time-scales, the continents have moved and changed shape. For a start, here's the Wikipedia entry on the geologic timeline of Western North America and the main article on the geology of North America. If we go far back into ancient paleo-history, the areas that are now the great plains were underneath the western ocean abutting the continent of Laurentia; the far west parts of our continent (like California's Sierra Nevada mountains) didn't exist yet because the Nevadan orogeny didn't occur until the late Jurassic era... but this is all a vast simplification. Like all questions of science - how many years do we want to spend on the topic to refine and perfect our understanding?
 * When I used to teach geology for small kids, we gave a brief summary suitable for early elementary school: you can find fossils of seashells in the mountains of Colorado and Utah because a lot of that land used to be the bottom of the ocean. Once again, we're so severely oversimplifying that we run the risk of lie to children-style factual error.
 * A great book, for the interested reader: The Geology of North America: An Overview (1989); available at Amazon. One reviewer wrote, "...very dense and pretty dry..." Well, what can one expect from a book on rocks?!
 * If we want to get very precise about the exact farthest west extent, and so on, all I can say is that I am reminded of our discussion in March, quibbling on the details about the exact age of Earth. How shall we measure west-ness in paleo-Earth?  Should we measure degrees of longitude, from the Greenwich meridian to the easternmost tidal high water mark?  ... and where exactly was Greenwich, so many million years ago?  These are, ultimately, issues that relate to false precision.  Paleo-geology is a different kind of science than analytical chemistry; geologists have to accept an amount of intrinsic uncertainty; and so we accept that we must maintain the scientific method without any ability to conduct controlled experiment.  But at the same time, we can hold ourselves to the highest standards of analytical investigative rigor.
 * Nimur (talk) 14:53, 10 July 2018 (UTC)
 * So in the case of the Great Plains, it matters how steep and long the slopes are from a plain or sea to the top of a piedmont plateau in order for it to be classified as a piedmont plateau and not just a high plain? Willminator (talk) 14:42, 10 July 2018 (UTC)
 * The U.S. Geological Survey's scheme for classification is centered around the idea of a "geological province," which is a concept they invented to group areas that have similar geological histories (and therefore, similar geological properties). But they use terminology fluidly: a region has specific areas that "exhibit the geology of the interior plains," even if there are counter-examples.
 * The term "piedmont" is used to refer to a specific, different area of the United States. In that sense, which is the canonical usage defined by the USGS, the word "Piedmont" is used as a locale, not as a generic description.  For more information on this standardization of terminology, Wikipedia has an article on United States physiographic regions.
 * Nimur (talk) 14:53, 10 July 2018 (UTC)


 * I think the key thing that makes a plateau a plateau is that you can look up at it. According to the article, it is "raised significantly above the surrounding area".  In the case of the Piedmont Plateau, there is an edge called the Atlantic Seaboard fall line.  Though it's an obscure feature now, apparently at one point it meant a bunch of sweaty guys had to lug a canoe a long distance uphill practically any way they tried to boat inland, so it counted as a highly noticeable feature to them.  The Great Plains don't have this AFAIK. Wnt (talk) 16:12, 10 July 2018 (UTC)
 * The Atlantic Fall Line can be quite dramatic in places and there's a clear delineation, for example, between the Atlantic Coastal Plain and the Piedmont all up and down the East Coast, from the Metacomet Ridge in Connecticut to the The Palisades in New Jersey. If you've ever crossed the George Washington Bridge, you're basically staring at the escarpment that marks the Eastern edge of the Piedmont.  I live in Raleigh, NC which lies right on the fall line, and it's obvious when you're approaching it: South and East of Raleigh is flat: there's very little hills or elevation changes.  In Raleigh, there are some fairly dramatic elevation changes in the area of the North Hills and the Crabtree Valley which clearly mark the transition to the Piedmont.  There's also an even more dramatic transition from the Piedmont to the Appalachians, the Blue Ridge Escarpment, which you notice dramatically on any highway going west through the Carolinas or Virginia.  By contrast, when traveling West across the Great Plains, there's no dramatic escarpments or changes in elevation.  It's true that the great plains can get quite high as elevation gradually ramps up from East to West, but there's no clear boundary the way there is for the Piedmont.-- Jayron 32 23:47, 10 July 2018 (UTC)


 * Here's the Palisades. There's still ridges of ancient metamorphic rock east of them, only about half the height of the Palisades at the GWB though. Beyond West Bronx and the skyscraper district with the tallest non-Manhattan building there's still naked eye hills over 200 feet above sea level but they're just piles of glacial detritus like terminal moraines. Sagittarian Milky Way (talk) 02:57, 11 July 2018 (UTC)

High index lenses
Are there any disadvantages to a 1.74 high index lens compared to one of lower index such as 1.67? I.e. Why doesn’t everyone with strong prescriptions get 1.74 instead of 1.67? Clover345 (talk) 07:52, 10 July 2018 (UTC)
 * Cost. Tigraan Click here to contact me 09:54, 10 July 2018 (UTC)
 * Agreed. I have terribly myopic eyesight and shell out the extra for the high index lenses. When it comes time to pick out lenses, my optician and I typically have to sift through several pages of various strengths and coatings to get some reasonable trade-off between price and utility (fashion falling a distant third). People requiring the higher index lenses also typically require other modifications as well, driving up the price again. For example, my optician makes several modifications to the grinding of the edges to reduce glare simply because there's more lens there to cause it. Matt Deres (talk) 12:20, 10 July 2018 (UTC)


 * I have one of each. My eyes are strongly asymmetrical and although my prescription for one eye is strong enough to justify high index lenses anyway, I get a more mechanically balanced pair of lenses if the thicker lens is made thinner, but not the thinner one, so they end up matching more closely.  It also has an effect on opacity for sunglasses.
 * Of course, graded index lenses would be even more interesting. Andy Dingley (talk) 13:28, 10 July 2018 (UTC)
 * While cost is a big factor, it isn't the only disadvantage. Coatings was mentioned above, but not clearly mentioned is one reason for coatings is because of the lenses. Higher index lenses generally mean more reflections, hence why nearly all high index lenses come with AR coatings. (And that can lead to other things like scratch resistance.) This is mentioned in the above linked source about cost but is also discussed here [//www.2020mag.com/article/ultra-high-index-using-it-wisely-and-well]. As mentioned there you also tend to get more chromatic aberrations, or other distortions of peripheral vision with high index lenses. (Also mentioned here [//www.specsavers.com.au/help-and-faqs/why-am-i-experiencing-peripheral-distortion-when-wearing-my-new-glasses].) Although as mentioned, this tends to be a bigger problem for those with low powered prescriptions because those with higher powered ones are often more used to limitations of their peripheral vision. As sort of hinted there and also mentioned above, it also depends on the skills of the optometrist or whoever is designing the glasses/dispensing the prescription, along with choosing the best option, working with the patient. See e.g. [//www.optiboard.com/forums/showthread.php/37641-Base-Curve-periphery-issues] [//optom.on.ca/Documents/Symposium/2017/Handouts/1.13-Dispensing%20the%20High%20or%20Unusual%20Rx%20-%20Fitting%20Edging%20%20Dispensing%20OAO%20April%202017.pdf]. As mentioned in a the second source, a notable advance is using computerised tools to give a more precise individualised solution generally called digital, HD or free-form lenses [//columbiaeyeclinic.com/traditional-vs-digital-eyeglass-lenses/] [//www.2020mag.com/article/digital-lens-basics-what-you-need-to-know]. Nil Einne (talk) 15:47, 10 July 2018 (UTC)

How do Voltage converters deal with Hz?
Do voltage converters from 220/240 to 110/120 or from 110/120 to 220/240, normally also convert the between 50 and 60 Hz? I know most devices won't need a converter anymore and that this might be indifferent for most appliances, but sometimes it matters. --Doroletho (talk) 18:34, 10 July 2018 (UTC)
 * No. It's rarely necessary to do this.  When it is, it's usually easier to replace the 60Hz motor with a 50Hz one  (it's almost never necessary to do it the other way). For US machine tools imported to Europe, it's sometimes necessary to do this because poorly designed motors overheat on 50Hz as their design was marginal in the first place. Andy Dingley (talk) 20:30, 10 July 2018 (UTC)
 * And besides motors, are other devices affected by the 'wrong' Hz? Some devices set their internal clock through the electric power. Wouldn't these be heavily affected, specially if they run on a timer and require exact running times? --Doroletho (talk) 21:12, 10 July 2018 (UTC)
 * A timer or synchronous clock doesn't just require conversion, it needs accurate conversion. Such a thing is possible, but I've never seen anyone bother to do it. We do already have clocks in Europe - it's cheaper to just use a local one. Andy Dingley (talk) 21:19, 10 July 2018 (UTC)
 * Some clocks do use grid frequency to synchronize (at least in Europe). Of course, a 50/60Hz mismatch would make the clock completely useless, not "slightly missing on the precise time". Tigraan Click here to contact me 08:57, 11 July 2018 (UTC)
 * Another device that the frequency affects is a transformer, though 50 and 60 Hz are close enough that I don't think it's likely to matter. See Transformer. --76.69.47.228 (talk) 09:40, 11 July 2018 (UTC)
 * Not true. A transformer designed for 50 Hz will run well at 60, but a 60 Hz transformer may overheat when run at 50. Akld guy (talk) 22:05, 14 July 2018 (UTC)
 * Most converters don't change the frequency. It is possible to get "inverters" or "frequency converters" that do this, though even the cheap ones are generally hundreds of dollars.  Most electronics don't care about the frequency very much, and of those that do (e.g. things with motors or cheap timing circuits), it is often easier/cheaper to buy a version that is designed for the local frequency than it is to import a foreign version and buy an inverter.  Dragons flight (talk) 08:20, 11 July 2018 (UTC)