1. Sound
Sound waves are longitudinal waves because the vibrations of air molecules is parallel to the direction of wave motion.
Look at tuning fork – as it
moves forward from
equilibrium, it creates a
compression in the air,
and as it moves backwards,
it creates a rarefaction.

2. Sound
Frequency is the number of vibrations per unit of time (unit is Hz).
Humans can hear frequencies between 20 and 20,000 Hz. Frequencies below 20 Hz (infrasonic waves) and frequencies above 20,000 Hz (ultrasonic waves) are also considered to be sound waves because they are still created in the same way through the same medium.

3. Sound
The frequency of an audible sound wave determines the pitch of the sound.
Pitch is a measure of how high or low a sound is perceived to be; it depends on the frequency of the sound wave.
Sound waves travel through different mediums (air, water, solids) and the speed of the sound wave depends on how close the molecules in the medium are. Sound waves travel faster through solids than through gases. The temperature of a medium can also affect the speed of sound.

4. Sound
Sound waves travel in three dimensions in a spherical pattern. This can be represented by showing a series of circles with each circle representing the wave compressions. λ

5. Sound
Rays point in the direction of wave propagation.

6. Sound
Doppler Effect – the observed change in the frequency that you hear by moving closer or further away from a sound source.

7. Sound
Intensity – the rate at which sound energy flows through an area.
Remember that power is defined as the rate of energy transfer, so intensity can be described in terms of power.
Intensity = P/4πr2 area of a circle
Intensity = power / (4π)(distance from the source) 2
This says that the intensity of a sound wave decreases as the distance from the source increases. This is because the same amount of energy is spread over a larger area.