How come people say 5,000 km and not 5 Mm?
why not just say millions of meters or Mega meters?
Main reason is nearly no one needs to measure things in megameters. Megameters would be a unit to measure the diameter of planets in, maybe the orbital altitudes of some moons. Our moon for example is ~384Mm away. Distances between planets, distances between stars, and distance between galaxies are many, many orders of magnitude farther than that.
As most of us rarely travel more than 1,000 kilometers very often, it’s the biggest unit most people are familiar with on an intuitive level.
I’m still convinced people don’t actually use the metric system’s power of ten design. Like no one uses centigrams or kiloliters either. They’ve picked out units that are pretty close to the ones in the Imperial/Customary system, kilograms are used instead of pounds, grams are used instead of ounces, kilometers are used instead of miles, meters are used instead of yards, centimeters are used instead of inches, millimeters are used instead of sixteenths of an inch and so on. Want to confuse a European? Draw up some blueprints in hectometers.
Yeah, the everyday usage is limited to, well, everyday sizes.
As you pointed out there is no difference in everyday usage. But for anything outside of the most trivial of comparisons, the imperial system breaks down hard.The advantage of the metric system is the possibility to scale both bigger and smaller when you need it, and always does so with a consistent factor. Sure, not needed when you want to know how many 8 cm strips are needed to cover 50cm. But for 1m? With inches and yards you already have to handle two conversation factors. How many sixteenth of an inch do you need to cover a foot? 192. Possible to calculate, but not nice and you’ll approximate with 200 if you need to do some calculations in your head. How many feet are in a mile? 5280. And yards? 1760. Do you really know these conversation factors? Do you want to calculate "there’s a street light every 30 yards, the street is 2 miles long, that’s xx streetlights? Or “there’s a street light every 30 meters, the street is 3.2km long, that’s 3200/30 = 107 streetlights”?
Oh, and the weird units do actually get used when it is a convenient size.
Cooking uses lots of in-between units for example. Centiliters (cl) are common in cocktail recipes or for shots, in some cookbooks you will find dekagrams, etc.
Hectare is commonly used to give area measurements (it’s origin is hekto-are, and “are” in turn is hekto-square meters, though “are” is not commonly used.). Want to convert hectare to square kilometers? Simply divide the number by 100! 3000hectare of forest burned down? That’s 30km^2, so 5kmx6km. Easy to visualize. The US customary system makes such conversations really really really hard. How many square feet, yards or miles are in an acre? I just looked at the Wikipedia page and there is no way anyone will be able to convert an area given in acre into “well, it’s approximately x by z miles”. Or “my house have xx square foot of living space, so that’s yy acres”.Btw, no one uses kiloliters, because that’s equivalent to cubic meters. Easy conversions!
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.
Would it surprise you to know that there is a unit of length that is specifically the distance between the earth and the sun?
It’s called Astronomical Unit.
Familiarity I guess. Mega isn’t really a widely used prefix outside of computers. We even say tons instead of megagrams.
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.
I wish we would. It sounds awesome to say.
Be the change you want to see!
Hopefully, you have many opportunities to use it.
I do. Unfortunately, I don’t have many opportunities to do so. Which may be the reason why people don’t say megameter.
