All sound starts with the vibration of some object or substance. The speed of that vibration depends upon the objectΓÇÖs relative elasticity, density and size.
If you pluck the end of a wooden ruler, a length of which projects over the edge of a table, you can see it vibrating. You can probably hear it too. The shorter the projecting length of the ruler, the faster the vibration. The note it makes gets higher. The highness or lowness of a note is thus defined by observing the frequency of this vibration. Frequency is measured in cycles per second (cps), or units of herz. In the case of the ruler, a cycle consists of the projecting bit going up, down, and returning to its original position.
