Elongation of a pendulum??? Not really a specific question just something in general. When discussing simple pendulums (a ball on the end of a string) or any system involving strings, my textbook always refers to something as the "elongation" of the string? Before this, I had never heard of this! When you swing a pendulum, is the string longer at some times than others? How does that work? What causes this? What effect does it have on the motion of the pendulum? I asked a professor today and he said something like a string can be considered as something like a spring that can be stretched, but not compressed, and there can be a spring constant associated with it. If this is so, then why doesn't this "elongation" factor show up in equations like ω = √(g/l) for the simple pendulum, and what does it mean for the normal modes of coupled pendulums? I was trying to ask him all these questions, but his English isn't so good to have a long discussion.