1. Sound

2. Sound waves are… What type of waves are sound waves? Mechanical waves
They need a medium to move through.
They are longitudinal waves because they are made of compressions and rarefactions and cause the medium to vibrate in the same direction as the wave

3. Speed of sound Speed of sound varies, depending on the medium
Travel fastest in solids, slowest in gases
Speed of sound = 342 m/s (in air)
THAT’S 765 mph!
In water speed of sound = 1798 m/s
Travels fastest in the most dense media
Why??
Because the particles are closest together so they easily bump into each other passing the energy along

4. Intensity is measured in decibels (db)
Intensity: the rate at which a wave’s energy flows through an area
Sound intensity depends on:
Amplitude – density of compressions
A greater amplitude (closer compression) means more energy is passing through the wave
Distance from source - closer to source the more intense the vibrations
This is why you can “feel” the bass when close to a speaker
Intensity is measured in decibels (db)

6. Frequency
Frequency of a wave in general means how many waves appear in a given amount of time
Frequency of a sound wave depends on how fast the source is vibrating
The faster the source causes vibrations, the higher the frequency

7. Pitch How high or low a sound seems to be
Depends on frequency, therefore on wavelength
High frequency (short l) sounds are high pitched
Low frequency (long l) sounds are low pitched.
Human ears hear sounds between 20 and 20,000 Hz.
We hear best between 440 & 7000 Hz

8. Sound Test

9. The Doppler Effect (of sound waves)
Doppler Effect: a change in sound frequency (pitch) caused by the motion of the sound source, the listener, or both.
Note: The sound is still being produced at the same frequency at its source, the air compressions change frequency by movement of the source.