Download What is sound?

Part One
World of Sound
 Everyday
your world is filled with a
multitude of sounds.
 Sounds help us communicate.
What is sound?
 Sound
is a pressure disturbance that
moves through a medium in the form of
longitudinal waves.
 Waves
of sound energy move outward in
all directions from the source.

Sound or pressure waves are
made up of compressions and
rarefactions.

Compression happens when
particles are forced, or
pressed, together.

Rarefaction occurs when
particles are given extra space
and allowed to expand.

One compression and one
rarefaction is one wavelength.
 Without
a medium there are no particles
to carry the sound waves.
 In
places like space, where there is no
atmosphere, there are too few particles to
transfer the sound energy.
How we hear…
 Sound
travels to your eardrum and causes
your eardrum to vibrate. This vibrates the
tiny bones in your ear the vibrations travel
into the cochlea.
 there are hundreds of special cells attached
to nerve fibers, which can transmit
information to the brain.The brain processes
the information from the ear and lets us
distinguish between different types of
sounds.
 Show: DSN What is Sound
Why are sounds different?

As you know, there
are many different
sounds.
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Fire alarms are loud.
Whispers are quiet.
Sopranos sing high.
Tubas play low.
every one has
different voices.

The differences
between sounds are
caused by
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Intensity
Loudness
Pitch
Frequency
Tone
Intensity
 Intensity
is the amount of energy a sound has
over an area.
 Amplitude is a measure of energy.
 The more energy a wave has, the higher its
amplitude.

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
As amplitude increases, intensity also increases.
As amplitude decreases, intensity also decreases.
Larger amplitude = higher intensity = louder sound.
Loudness
 We
are used to measuring the sounds we
hear in loudness (volume).
 Loudness cannot be assigned a specific
number, but intensity can.

Intensity is measured in decibels (dB).
 Listening
to loud sounds, sounds with
intensities above 85 decibels, may
damage your ears.
 120 decibels is the threshold of pain.
Sounds and their Decibels
 Defense
Siren…130 dB
 Rock Concert…110 dB
 Lawn Mower…100 dB
 Motorcycle…90 dB
 Vacuum Cleaner…70 dB
 Normal Conversation…60 dB
 Background Noise…40 dB
 Whisper…20 dB
Pitch
 Pitch
helps us distinguish between low
and high sounds.
 Pitch depends on the frequency.
 High
pitches have high frequencies and
 Low pitches have low frequencies.

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Thunder has a frequency of only 50 Hertz,
while a whistle can have a frequency of
1,000 Hertz.
Show: What is Pitch
Tone
 Tone…
or sound quality.
 When a source vibrates, it actually
vibrates with many frequencies at the
same time.
 Each of those frequencies produces a
wave.
 Sound quality depends on the
combination of different frequencies of
sound waves.
Sound vs. Noise
A
sound must have an identifiable pitch, a
good or pleasing quality of tone, and
repeating pattern or rhythm to be music.
A
noise on the other hand has no
identifiable pitch, no pleasing tone, and no
steady rhythm.
Ultrasonic and Infrasonic waves
 The
human ear is able to hear frequencies
of 20 Hertz to 20,000 Hertz.
 Sounds that are too high for us to hear are
called ultrasonic waves.
 Sounds that are too low for us to hear are
called infrasonic waves.
 Show
Hearing Test
Why do we see lightning before
the thunder?

The flash of light from
lightning travels at about
300,000,000 m/s or 186,000
miles per second.
 Sound travels at about
0.2 miles per second.
 It takes sound nearly 5
seconds to travel 1 mile.
Sound and Speed

Speeds of Sound in
different mediums
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Sound travels faster
through materials that
are more dense.
Rubber …60 m/s
Air at 40 °C… 355 m/s  The speed of sound
Air at 20 °C …343 m/s
through the air
Lead …1210 m/s
depends on the
temperature.
Water …1482 m/s
Glass …4540 m/s
 The speed of sound
Copper …4600 m/s
increase by 0.6 m/s
Aluminum… 6320 m/s
with every increase of
1º C.