The trough is the lowest point on the wave. A node is a point on the wave that does not move. Talk about how waves must travel through a medium. Waves in the ocean travel through the water. Waves in the desert travel through the sand.
Sound waves travel through the air.
Have a student help you demonstrate this with the Slinky. Have them demonstrate and identify the parts of the wave. Frequency relates to pitch. A high note or sound has a higher frequency than a lower note or sound. Use the waveboard to demonstrate changes in frequency.