Compare results to class. Use four different objects. A-D. Make six or more of each type of tube to give everyone in class something to do all the time. B. Vocabulary enrichment. Need vibrations to make sound.
Pitch is determined by the length of the air column.
B. Cutting off the straw is the same as cutting a hole in it - just more permanent. C. Clarinets, oboes, saxophones, etc. The string has to be tight and not touching any other object. See if anyone observes that the phone won't work if the string goes slack or around a corner. This is the speed at which the wave travels - the speed at which the ripples in the pond move.