Hertz (Hz) is the unit we use to measure frequency. The more hertz, the more waves per-second there are. When humans hear more sound waves in close succession, we perceive it as a higher pitch. This video demonstrates the entirety of the average human hearing range and shows how many waves we are hearing at that point.

A neat thing about this exhibit is that each pipe has the frequency of its note written on it – the larger the number, the higher-pitched the sound that the pipe makes. Different musical notes are related to each other by how many times larger the frequency of one note is than the other. For instance, the lowest pipe has a frequency of 52Hz. Can you find a pipe with a frequency double that? Try playing those two notes over and over alternately. In music we call this particular difference an octave and we say that these two notes are the same note in different octaves. See if you can find other notes on here that are double or half the frequency of a different note.