How come people say 5,000 km and not 5 Mm?
why not just say millions of meters or Mega meters?
Jokes on you elite dangerous uses Mm/s for lowest speeds in supercruise before it changes to “c” for relative to light speed
Familiarity I guess. Mega isn’t really a widely used prefix outside of computers. We even say tons instead of megagrams.
And yet we say megatons.
Yes, I think it’s a question of use. I can’t think of many examples where you would quickly need to know the measurement to the nearest Mm. Maybe if for some reason you deal with a lot of lunar orbits? Diameters of exoplanets?
Any earth distances we need to know with greater precision, and any stellar distances are probably better measured in light years, etc.
Odometer readings
“I’ve driven 112.326 megameters” takes the same amount of time to say as 112,326 kilometers. 🤷♂️
To be fair, mass is weird because the base unit is kg (yes, the name includes a prefactor). I have no idea how they managed to fuck it up that badly.
Not much need to use Mm, it doesn’t come up very often. So when it does it’s easier to use thousands of km so as to not confuse people with “another” measurement.
On Earth it’s just not needed. In nearby space it could make sense — distance to the Moon is 369 Mm. Distance to the Sun 149 Gm. But people aren’t good at visualizing the difference between kilo-, mega-, and giga-. It isn’t obvious from those numbers just how much further away the Sun is.
I’ve seen megameters used in the context of astronomical distances, but not terrestrial ones. I think terrestrially, the familiarity of kilometers helps with a sense of scale.
The beauty of the metric system is you don’t lose a sense of scale from using a higher unit because you can intuitively know 1Mm is 1000km.
Megameters sounds scary and I don’t want to alarm the people I’m talking to.
nobody will stop you, i’ve seen some publications use gigagrams instead of thousands of tons
weirdly enough SI unit for mass is kg not grams
My physics teacher once told us that this was due to the influence of disciplines that calculate with huge masses, say in astrophysics the weight of a planet or the the amount of oxygen within it. Don’t know how much of it is true but the basic tenet of everyone preferring the numbers that they work with on a daily basis having as few prefixes as possible as it makes mentally handling and remembering them easier.
