Vibrating Tuning Forks Dipped in Water
A vibrating tuning fork is dipped in a cup of water. The tuning fork stays in place as held but the water waves propagate away from the source.
A naked speaker is set to a low frequency and some styrofoam chips are set on its rim.
Show video of tuning fork and air molecules... note that each air molecule oscillates in place just like tuning fork but wave of sound transmits through air due to the air vibrations.