Hi, I have a few questions about Sonometers which I've attempted to think through - though I may be missing something. Perhaps someone can fill in any gaps for me? If I was to be asked why only 'discrete modes' of vibration can exist for a sonometer, is it enough merely to talk about the fact that this involves standing waves, and for a standing wave you must have "nodes" at either end, and that this is only possible for wavelengths that satisfy 2L/n (where n is an integer), and consequently only possible for frequencies that satisfy vn/2L? As I understand it, what determines the wavelengths is simply the length of the wire we provide. The frequency, on the other hand, is also a function of the velocity of the wave, and this in turn is dependent on the tension of the wire and its mass per unit length. [I believe waves travel faster on a tighter string (but why?), and slower on a more massive string (which seems fairly obvious).] So finding the 'resonant frequency' is a bit more complicated, since it isn't just dependent on the wavelengths that the wire will permit, is it? Another question I have is this: if I was to place my finger lightly in the middle of the wire, would I be, in effect, altering the length of the wire, or merely encouraging a standing wave with a node in that position (eg. the second harmonic) to form?