So the theory is that R vibrates with largest amplitude due to resonance. Because when measured from the common beam its length is the same as that of A, so A's vibration would pass to R the same amount of energy R would have vibrating on its own. Right?
My question is, how come the lengths have to be measured from the common beam? It just oscillates about the point on the string where it was fixed, so shouldn't that be the point from where you measure length if you want to get the right values of energy?
I've been thinking , if you measured the lengths of one of the smaller pendulums, one from the common beam and the other from the string, and also measured its time period, which length would correspond to that time period?
I know that the common beam is the right one, because I saw R vibrating with high amplitude with my own eyes. (It threatened to knock my eyes out ☺) I just want to know why, because theoretically it seems to me that it should be from the string.