thats the beauty of physics. i mean i'm 16 and i love this subject. its fantastic. I think... how is it that all these formulas just work... I still haven't found an answer. but i think that some of them have been made by humans.
eg. velocity = m/s
distance was just thought of by some genius frenchman who probably picked up a stick and sayed "lets call this length a 'metre'".
where time itself isnt really a creation of humans, we can measure it. So one day someone sayed "from this point in time to..." 60 seconds later "...here, will be a minute, and we shall divide that by 60 and they shall be seconds". or something like that (HAHA)
but velocity is simply a ratio between how many metres are travelled every second. i hope this helps ^_^
