It's called the "partitive article": http://italian.about.com/library/fare/blfare125a.htm
I wrote force and it was marked wrong. There is a big difference between "force" and "power". Force is the direct translation of forza. Power would be potere. Force should be correct. One has power (must be earned) when people believe in it and do what they should do. Otherwise force has to be used. Therefore money (numbers) is force, not power. Read the book of H. Arndt.
I still don't get it. This "partitive article" is not required if somebody don't want to say "some", yes? So I can say "C'e forza nei numeri" and there is answer "There is strength in numbers"? Than it is wrong translation, should be "There is SOME strength in numbers" right?