Sound Waves and Particle Vibration

Study Notes

Sound waves are vibrations passed on between particles, not a direct travel of air particles from the object making the sound to the ear.
When an object vibrates, it pushes on the air particles next to it, causing them to vibrate and pass on the movement to adjacent particles.

Air particles move back and forth, but do not actually travel anywhere, instead passing on the vibration to neighboring particles.
Particles vibrate in the same direction as the wave travels.

Loudness of a sound depends on the amplitude of the vibration of the air particles.
If air particles move back and forth a lot, we hear a loud sound.
If the source of a sound makes the particles vibrate more gently, we hear a quieter sound.

The number of vibrations each second is called the frequency and is measured in a unit called hertz (Hz).
The lowest pitch sound that most humans can hear is 20 Hz.
The highest pitch sound the average human can hear is 20,000 Hz.

Wave traces appear on an oscilloscope graph as a transverse wave, but are actually a longitudinal wave.
Wave traces show how big the vibration of the air particles is on the vertical axis against the time on the horizontal axis.
A loud sound makes the air move back and forth a lot, resulting in big peaks on the graph.
A quiet sound makes the air vibrate back and forth less, resulting in smaller peaks.
A high pitch sound has a high frequency, making the air vibrate quickly, resulting in closer peaks.
A low pitch sound makes the air particles vibrate more slowly, resulting in peaks that are further apart.

If there is no sound, the wave trace is a flat line.
The amplitude of a wave is how high the peak of the graph is compared to the flat line.
The higher the pitch, the more peaks there are (the frequency of waves).