How are proportionality constants in physical relations determined?

[Syed Ammar]

I wanted to ask how are the values of proportionality constants in physical relations determined. How do we come to know their exact values ? An explanation with an example please...

 

[SteamKing]

I wanted to ask how are the values of proportionality constants in physical relations determined. How do we come to know their exact values ? An explanation with an example please...

Which proportionality constants do you have in mind?

If you are talking about something like G (the universal gravitational constant), its value is determined through careful experiments. The value obtained is not exact (how could it be?), and there is usually a precision associated with each constant, since different experimental methods have different levels of precision associated with them. For instance, G is the one physical constant which is least precisely known.

http://en.wikipedia.org/wiki/Gravitational_constant

 

[Syed Ammar]

Can you elaborate on constants of other fundamental forces like k in Coulomb's law?

 

[rumborak]

While in the beginning, when Charles-Augustin de Coulomb postulated the law named after him, "k" had an empirically derived value, it now has a precise value, because you can calculate it from other constants. The Wikipedia article on the constant lays out the derivation quite nicely.