I'll pose that as a general question, and specifically for sound waves, which Googling did not answer in a satisfactory way. And a specific instance I'm concerned with is as follows: - Students are using telephone cords to make waves (cheaper and much more durable than Slinkies!). - Most groups hold the cord stretched through the air. - But one group put the cord on the floor, and snapped it sideways to generate a wave. Especially at higher amplitudes (more sideways) the cord rubs a lot on the floor. We are debating, to no conclusion: does that friction affects the measured speed of the pulse?