Students can be instructed on how to make the hummer, or ask them to look at a model and figure out how to make it themselves (skills in careful observation, trial and error testing).
Put the erasers on the end of the posicle stick.
Cut the index card so that it fits between the erasers, then staple it to the popsicle stick.
Tie the string onto the posicle stick, beside the index card.
Stretch the rubber band around the erasers.
Hold the end of the string and swing the hummer around your head.
Tip: the rubber band must be flat (not twisted) for this to work.
Discuss how the sound is made:
As the hummer moves it makes the rubber band vibrate. The index card amplifies the sound.
Students can try changing the rubber band to see how it changes the sound.
When trying different rubber bands, the flat ones seem to work best.
Not sure why sometimes two notes are heard - maybe harmonics?
Instead of erasers, use corks or tape.