Chapter 1: Song

Water Waves

You cannot begin the study of wave-motion better than by examining carefully the waves which travel over the surface of a pool of water when a stone is dropped into the middle of it. Where the stone drops there is at first produced a depression, which immediately begins to spread outwards from the center of disturbance in the form of a circular trough.

Upwards and Downwards

The disturbance which travels to the edge of the pool is caused, not by any bodily motion of the water outwards, but by a downward motion of the water-particles, which spreads outwards from point to point. The downward motion is followed by a swing upwards, producing a crest, which follows the trough and travels after it. By this succession of moving throughs and crests is produced by a series of ripples or water-waves. The distance between one crest and the next, or between one trough and the next, is called a wave-length.

The Song of the Green and Golden Bell-Frog

Play video to hear the Green and Golden Bell-Frog

A (ground-dwelling) tree frog of Eastern Australia

Activity: Listen In

Close your eyes and listen to the sounds around you. Imagine the spherical 3D sound waves emanating from the 'songs' surrounding you - whether technological or natural. What is the source of these 'songs'? What is the vibratory motion that produces them? Next time you are outside, stop and take a listen. Can you hear the too often forgotten songs of animals?