SOUND - is a form of energy produced by vibrating matter.
- When we speak our vocal cords vibrate to create sounds.
- Example: If you shoot a gun under the water, molecules of the water will vibrate and carry the sound a long distance.
- Sound is transmitted in waves.
- Sound uses compressional waves.

COMPRESSIONAL WAVES - a wave where matter vibrates in the same direction as the wave travels.
- NOTE: compressional waves are also called longitudinal waves.

Compressional waves act as a coil spring

Where the coils are pushed
together (compressed) is called
an area of compression

Where the coils spread
apart is an area of rarefaction
 

Like transverse waves, compressional waves have wavelength, frequencies, amplitudes and velocities.

The greater the amount of compression of each wave, the greater the amplitude and the greater the energy carried by the wave.
NOTE: In a sound wave greater amplitude means greater volume (loudness) of the sound.

Sound waves are compressional waves produced by vibrating matter.

Unlike electromagnetic waves (transverse waves) sound must be transmitted through matter, without matter there can be no transmission of sound.

Speed of sound - depends on the matter that carries it. Speed = distance that the sound wave travels in a unit of time. Speed = meter/second (m/s).

Speed of sound in:
1. air (dry air) = 332 m/s
2. water = 1454 m/s
3. wood = 3828 m/s
4. iron = 5103 m/s

Notice that sound travels faster through liquids than gases and faster through solids than liquids.

LOUDNESS AND PITCH

TONE QUALITY - describes the differences among sounds of the same pitch and loudness (differences depend on the matter vibrating).

A sound can be soft or loud.

Intensity of a sound depends on the amplitude (compression) of the waves.

A loud sound produces a sound wave with a large amplitude.
NOTE: the more energy creating the wave the more amplitude (compression)
Example: If you hit a drum harder, the sound produced will be louder.

Amplitude of a sound wave can be compared to the height of a transverse wave.

loud sound
amplitude

soft sound
 
 

Loudness is measured using a unit called a decibel (dB).
- normal conversation is 60 dB
- a sound so loud that a person feels pain is 120 dB

FREQUENCY (of a sound wave) is the number of waves that occur per second.
F = waves/second

PITCH - is the way a person hears the frequency. Greater frequency means higher pitch.

- NOTE: The shorter the wavelength of a wave, the higher the frequency and therefore the higher the pitch.

The frequency of sounds that can be heard by most humans are between 20 hertz (hz) and 20,000 Hertz (hz). Remember - one Hertz (hz) is one vibration/second.

ULTRASOUND - sounds above 20,000 Hz.
- Many animals (ex. dogs) can hear frequencies well above 20,000 Hz.

NOISE - sounds produced by irregular vibrations.
- sounds at the wrong time and place.

ACOUSTICS - the study of the science of sound.