This demonstration uses a slinky and tuning fork to explain two types of waveforms in our world: transverse and longitudinal. A discussion on sound waves is included and leads to categorizing sound waves as longitudinal waves.
Recreate E.F.F. Chladni's classic demo of sprinkling sand on a plate and playing it with a violin bow to create and visualize various vibrational patterns. This versatile demo can be adapted to talk about sound wave acoustics, vibrational normal modes, and energy transport to a wide range of audiences.
Build a simple Chladni plate using a 6" x 6" metal sheet, a 2 watt speaker, powered with a 20 gain amplifier and phone. Sprinkle sand on the sheet, and play various sound frequencies to reveal the sheet's assortment of resonant vibrational modes.
Along with the plate demo itself, an amplifier can be made fairly easily with an LM386 op amp. Download instructions for making the amplifier under associated files or can be found here.