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this post was submitted on 26 Aug 2023
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Showerthoughts
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Units closer related to everyday stuff are those that stick around. Like horse power or km. People don't use Mm but instead 1'000s of km, even into the million km for cars. Even in space they still tend to use km like for the distance to the moon or sun. Only once the distances get absurdly large is there a shift to either another unit (light years) or the use of different notation (like 3.14E12 m).
As a Swede, using units that give numbers above ~100 starts to get unwieldy. Hence why we use mil (1 Scandinavian mile = 10 km) once we get to triple digits in km. "It's 60 mil to Stockholm" is immensely more natural than "it's 600 km to Stockholm".
That is fascinating! I had heard of the "metric mile" as being 1500m: the closest you can get to running a statute mile at international competitions.
But I like this 10km mile idea! We could use something like that here in Canada. Sometimes we say "klick" here to mean km, so I have tossed around terms like "decaklick" and "hectoklick" but people look at me funny.
We've had different mil definitions in Scandinavia before, but at some point Sweden and Norway agreed to unite at 10 km, which is a really useful unit. Denmark just didn't do it. They'll give distances in hundreds of kilometers.
I love this! Let's use all the prefixes!
It's always been a pet peeve of mine that Sweden is seemingly the only country that uses dl (deciliter) and hg (hectogram, but we just say hekto, just like with kilo), which are to me vastly more useful units as they're close to what you're measuring. 2 hg salami or candy or whatever instead of 200 g, and 3 dl water instead of 30 cl or, god forbid, 300 ml.
I see cooking shows from countries that normally use imperial, using metric by measuring everything in milliliters. It makes no sense! No recipe needs that resolution.
The astronomical unit AU is commonly used for things in the solar system. 1 AU is roughly the average distance to the sun, about 150 000 000 km
I measure my fuel consumption in square millimeters, thank you very much.
I get the joke. But it does not actually work. The unit is meter (to some power) but it is not the same meter. One is for a specific liquid, the other for a driving distance. That information was just omitted to begin with, since everyone knows what is meant with the regular units/expression. But when you would want to do that, you need to put that information back at the end.
I know the metre has been defined by earth's size, or other various things, all rather arbitrary. Wouldn't it make sense to define it by the speed of light and a light year, divided into even portions? Start by dividing a light year (in a vacuum) by ten, and keep dividing by ten until we get a unit that is close to the useful size we are accustomed to?
That way we could scale up, and I suppose that's going to be useful in the future.
It's already defined that way - from Wikipedia "From 1983 until 2019, the metre was formally defined as the length of the path travelled by light in a vacuum in 1/299792458 of a second. After the 2019 redefinition of the SI base units, this definition was rephrased to include the definition of a second in terms of the caesium frequency ΔνCs. "
Just because it's defined as some section of a light year does not mean it's using a light year as a reference. You could use a foot and find the fraction of a light year that represents it, but that doesn't mean that the foot is based on a light year.
I'm saying the short measure that we use on a daily basis might be a BASE 10 portion of a light year. Not 1/299792458 of a light second.
P.S. It's like being on Reddit, being download for conjecturing.
I see what you mean. That is just as arbitrary as using the Earth's size or any other reference. There's nothing special about a year.
Touché
My ignorance shows it's ugly face again.
it's a hard thing for me to wrap my head around, but it's cool when you think about it: there's actually no possible shared reference; even with atomic clocks, based solely on the bouncing of cesium atoms ticking away, the distance travelled is dependent on acceleration in your reference frame.
relativity really is!
Am not sure I completely agree with you. Some of the archaic units are still used because USA is so dominant in both technology and advertisement. People living in other parts of the world know exactly how much inch is or gallon. Just like most of the world knows English, even though it's not the easiest language to learn. Simply GB was too big and influential and they left their mark.
As far as Mm is concerned, why would you do that? If you were making a small panorama or model you wouldn't use 0.00001km, would you? You pick units that are most convenient for the purpose. Kilometers are used for cars and things related to traveling because fuel economy is expressed in such unit, car's own computer measures distance in same unit, speed is measured in same unit. Why would anyone use anything else? 0km until 1000km is perfectly intuitive scale which doesn't get crossed too much. For the very same reason that's why we use square meters to measure surface of a home, because they never go into square kilometers. And square milimeters is pointless.
It's all about practicality. SI system is great because it allows users to use same unit in different scale and have it be intuitive and easy to convert. Also when it comes to astronomy, there are many units you skipped there. LY is too big and rarely used unless it's to describe distances to other galaxies and size of those. There are AU as some one else mentioned. Earth size, etc. But rest assured when scientists are trying to calculate something, they still revert to good old reliable SI system.
Nobody knows what a gallon/yard/... is outside the USA.
English is super easy.
I don't get your stance on Mm. First you use it for tiny values and say that is stupid. Then you hint that going above 1'000 km the km should not be used anymore. Also, 1'000 km are nothing in terms of vehicles etc., driving that distance in one day is nothing super special. A car does 100s of 1'000 km. Hence my point.
I didn't skip anything, I named some examples to prove or better explain my point.