Why do they use quantities like 15,000 Kilometers? Why does one NEVER see that quantity as 15 Megameters?
Because people who use the metric system regularly have an intuitive feel for how long a kilometer is. Nobody just understands a megameter.
You don’t see gigagrams either, for the same reason. For units that the average person isn’t likely to have as intimate a relationship with, such as watts and joules, the prefixes are extensively used.
People use the metric system in pretty much the same way that Americans use customary units: they pick a unit that’s convenient to them (whether centimeters, meters, kilometers, etc.) and mostly stick with that within any given area of use.
Few Americans know or care that there are 5280 feet in a mile, because the things we measure in feet (heights, houses, etc.) and the things we measure in miles (transportation distances, etc.) don’t mix all that much. Probably a greater fraction of Europeans know that there are 1000 meters in a kilometer, but for the most part they don’t need to, because again the things they measure in meters and the things they measure in kilometers are different.
As Enginerd said, people develop an intuition for the scale of a unit–but this is dependent on the area of use. Few people have an intuition for how long it takes to drive 10,000,000 centimeters. But everyone in Europe knows how long it takes to drive 100 km. Conversely, people have a feel for the height of someone 200 cm tall, but not someone 0.002 km. Sure, they can work it out easily enough, but that’s no longer intuitive.
And as naita said, other prefixes are used, but in different contexts. Hardly anyone needs to know how big a gigawatt is. But people that plan power distribution systems do. Even there, they probably only have a good feel for it within the context of the system they’re working on–for instance, that a nuclear reactor puts out around a gigawatt. They might not have a good feel for how many houses they can power with the same output, at least not without doing a bit of mental calculation.
Whenever I refer to a week as “ten kilominutes” people look at me like I’m crazy.
“That’s right ! Three football fields ! [To accurately estimate range] You take what you know, then you multiply ! PLEASE don’t use your dicks, they’re too small and I can’t count that high. I don’t wanna hear 400.000 inches.”
– from Jarhead
Can’t argue with that Dr Strangelove, but I would add that in Europe the metre is very widely used. A house would be xxx sq metres; road signs will say “Travaux routiers à 1000 mètres” or “Lavori stradali a 250 metri.” In the UK, some councils started to use metres instead of yards on some signs but that was stopped and they use yards. An exception is for footpaths where distances are usually in kilometres.
Every trade seems to have its own preference: Timber is always in cms; engineers or architects use millimetres.
Nice one! That’s under 1% error. Never realized that.
I meant to celebrate my gigasecond day, but forgot. My 2 gigasecond day is still a ways off.
In some of Vernor Vinge’s books they use kiloseconds and megaseconds. A kilosecond is their hour-like unit and a megasecond a week-like unit. Makes sense if you’re on an interstellar craft and wholly decoupled from anything like a day or year.
You people have rods and leagues, but you never use them either.
Distances are in kilometeres on roads and cycle paths too! Metres are use to indicate features that are less than a kilometre away, whether they be temporary features like roadworks or permanant features like motorway off-ramps. Anything above that is measured in kilometres.
What, you never heard of Jules Verne’s book (and the later Disney movie) 20 Kiloleagues Under The Sea?
I like the giga-barn-lightyear for volumes, even if that’s a larger error vs. metric.
Exactly. How often would people generally need to use a megametre? It’s a big-ass distance so usually you would be choosing between expresing things as e.g. 0.75Mm or 750km, so stick with what you are used to. People use kilometres all the time so it’s the default option and extends up past what should be the Mm transition.
In a similar fashion the the hectometre gets very little love these days as most people either go up from the metre (e.g. 300m) or down from a kilometre e.g. (0.3km) when theoretically they should use 3hm.
It’s worth noting that the swedes & norwegians use a customary mile which equates to 10km - and that is still used quite a bit since it’s a nice convenient measure which everyone is familiar with. 30mil, 300km. If that was an official part of the SI system it would get a lot more use than the megametre.
On the other hand, the square hectometre, or hectare is the common for measuring land area in cases where the acre would be used in imperial.
In in some European countries, they used a unit called myrometer (10 kilometers), still to be seen on some old border stones.
Hectometers (100 meters) are also used in some fields. In Austria, they commonly use decagrams (10 grams), usually for small quantities of food. It sometimes confuses foreigners, even those who are otherwise familiar with the metric system.
In Germany, the use of Pfund (pound) which is equal to 500 grams has been actively discouraged at least since I was in school, but the Pfund simply won’t die. When I buy butter, it’s always half a pound (250 grams).
I’ll stick with the trusty light-nanosecond, and of course the cubic light-nanosecond for volumes.
The transition would be painful for any area accustomed to regular miles (which are less than one sixth of the length of that one).
~27 liters? A bit large for every day use, isn’t it?
We were so lucky to have miles around that length. A Norwegian land mile was 11.298 km, a Swedish mile was 10.687 km at the time we adopted metric.
Indeed, Brits in sweden often find a country mile really is a LOT further than they expect…