Question

how is one day only 24 hours only not more or less? how did they calculate?

Answer 1

its the time between sunrise and sunset.

Answer 2

should be the result after calculating T (period) \[T=2\pi r/\sqrt{GM/r} \] where G is the gravitational constant (not g), M is the mass of earth, and r is the radius of earth.

Answer 3

the answer is in seconds

Answer 4

That's a bit like asking why boiling point is 100 degrees C not more or less, or why a litre of water has a mass of exactly 1kg. Because someone defined it to be that way and it has stuck through convention and standardisation.

24 is a nice number because it is divisible by many integers, 2,3,4,6,12 so it makes sense to divide the day into 24 fractions.

I think it's important in physics to understand what has been calculated and what is exact because it has been defined that way.

Answer 5

it is just a standardisation! just like mass,length,ampere etc. are standardised in s.i system. its only for our convienience,to keep track of time

Answer 6

In the s.i system I know of six basic 'dimensions'
Length in meters
Mass in kilograms
Time in seconds
Temperature in kelvins
Currents in amperes
Luminous intensity in candela

Other physical units can be derived from these, so Force in newtons is \[kg* m* s ^{-2}\]
(sorry I cannot find the dot operator)
But that doesn't answer the question why a second is a second, not longer or shorter, why is the day split into 24 hours and not 50, 100 or 10. It's more of a historical question than a purely scientific one - but it's a good question because it helps understand the way these things are thought about.

As for how it was actually measured, probably with sundials of some kind. You know the earth was first discovered to be round and not flat because someone noticed the length of a shadow cast by a vertical stick at miday varied according to your distance from the equator?

If you know some calculus you might also understand why a second is called a second? 1/60th of 1/60th of an hour!