Sound waves are longitudinal waves. Their vibrations occur in the same direction as the direction of travel. Sound waves can only travel through a solid, liquid or gas.
When an object or substance vibrates, it produces sound. The bigger the vibrations, the greater the amplitude and the louder the sound.
A microphone converts sound energy into electrical energy in the form of electronic signals. A computer or an oscilloscope can be used to display these electronic signals, which show the same changes in amplitude and frequency as the sound waves.
Volume (amplitude) – shown by the height of the waves displayed. The larger the amplitude of the waves, the louder the sound.
Pitch (frequency) – shown by the spacing of the waves displayed. The closer together the waves are, the higher the pitch of the sound.
These diagrams show snapshots from oscilloscope traces of three sounds.
Diagrams 1 and 2 show two sounds with the same frequency (wave spacing) but different amplitude (the height of the trace).
The trace on 1 comes from a sound with a smaller amplitude than on 2. Sound 1 is quieter than sound 2.
Diagrams 2 and 3 show two sounds with the same amplitude but different frequencies (wave spacing). The faster the vibrations, the higher the pitch (frequency) of the sound.
The trace on 3 comes from a sound with a higher frequency than the one on 2. So sounds 2 and 3 are the same volume (amplitude), but 3 has higher pitch (frequency).