along the path of the wave. Note that the highest points of the curve lie beneath the places of maximum condensation and

the lowest points of the curve are beneath places of maximum rarefaction, while points of medium density are located in

between the two extremes.

(2) Since the wave is moving to the right, the ear of the listener experiences variations of pressure identical to

those existing along the wave illustrated in figure 3. First, the rarefaction farthest to the right and then the neighboring

condensation to the left and so on. This is taking place because the entire train of waves is moving toward the ear from

the left. The graph of pressure against distance at any instant and the horizontal distance may represent intervals of time.

(3) The curve of the graph

represents sound waves set up by an

object vibrating 400 times each second.

The time required for each complete

vibration as shown in the graph is

1/400th of a second, or 2.5

milliseconds.

b. The number of complete

vibrations of the object that occur

in one second is the same as

the number of cycles of the wave in

the graph that occur in 1 second.

This number is called the frequency of

the wave. A cycle is a complete set of

FIGURE 3. Waveform of Simple Sound