Question

Why don't units of seconds ever get The SI prefixes
that make them bigger
e.g. kilo seconds, mega seconds, ... [ks], [Ms], [Gs], ... . ?
Usually see , [ms], [s], [m], [hr], ..., [yr], ...

Why don't units of metres ever get prefixes
that make them bigger than kilo
i.e. [Mm], [Gm], [Tm], [Pm], ... ?
Instead we use say; 10^6 [km], or 2.7 [AU], or 6.7 [ly] for example.

Why dont kilograms ever have unit that make them bigger? , we either see [µg], [mg], [g], [kg], [t], 10[t], 10^24 [kg], ... .

Answer 1

Using the prefixes are not always the most efficient way to express a number, that's all. There's no reason why you couldn't use any of the prefixes you mentioned.

Answer 2

i guess it usually depends upon usage, how easy it is to interpret and how often do we have to come across it

for time, its much easier to convey the information using hrs, days, weeks and years, rather than using kilo seconds or mega seconds don't u agree?

For mass, we use TONS for 1000 kg, this is historical and so again its easier to just say 1 ton rather than saying 1Mega gram. Also for masses, we don't usually deal with masses more than say 10,000 tons?.. till then we can definitely keep using tons. Then usually we encounter astronomical masses, which definitely are so huge u can't use any prefix for them , thus we use solar masses.

but u have a valid point in meters, and i guess the reason being, for general public its hard to remember a lot of prefixes. As science students for us its very easy. And i think for that reason they made sure when computers came along they forced us to use appropriate prefixes and get used to it :D. but u ask most of them, they won't know whats the meaning of GIGA and MEGA or TERA.

Answer 3

Mash has given the best of answers. Usage rules in this area.
Some habits differ among nations, even the ones who have been metric for 200 years: the French NEVER use dag or hg, whereas the Italian use hg daily at the delicatessen.

Answer 4

It takes me only an attoyear to come up with a good reason for why this is how it is.