Why are there so many units and time?

Answer 1

Because we observe and work with such a huge range of speeds ... from the motion of tectonic plates
at around 0.4 inch per year, to the speed of light at around 300,000 kilometers per second (about 1 foot
per nanosecond ... another new unit forspeed).

The purpose of having a lot of different units for the same quantity is so that whether you're observing
a tiny version or a gigantic version of that quantity, you can always find a unit that gives you a convenient
number ... a number that's easy to write down, remember, and tell other people about.

If the only unit we had for speed was my walking speed ... call it 'W' ... then the typical motion of
a tectonic plate would be something like 0.0.000000000473 W , and the speed of light would be
something like 223,539,000 W . . . neither of those numbers particularly easy to handle. People
a long time ago would have invented the nano-W, the micro-W, and the giga-w, to cover the
enormous ranges of speeds that are completely outside of our daily experience with things
walking, driving, flying, or swimming across the face of the Earth.

Answer 2

There is so many units and times because when we use time we can use units.

Answer 3

Depending upon the time taken and distance covered, different units can be considered. Hence, different units are used.

Answer 4

Only two units are frequently used around the world: m/s and km/h.
Other are only regional units used in US, Canada, UK and some regions from Africa or Asia.