# SOL 5.2 a, b, c, d March 2013

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29 Νοε 2013 (πριν από 4 χρόνια και 5 μήνες)

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SOL 5.2 a, b, c
, d

March 2013

Sound Notes

Sound
is a form of energy
produced and transmitted by vibrating
matter
.

Sound waves are compression (longitudinal) waves.

When compression (longitudinal) waves move through matter (solid,
liquid, or a gas),
the molecules of the matter move backward and
forward in the direction in which the wave is traveling.

All sound energy is produced by vibrations.
Vibrations

are the back
and forth motions of objects.

All sound moves through matter (solid, liquid, gas).
Sound cannot move
through a
vacuum
, because there are no molecules to vibrate back and
forth.

The strengthening of a sound wave is called
resonance
.

Sound travels in
compression waves
.

As sound waves travel, molecules are pressed together in some parts,
ca
lled
Compression

and in some parts are spread out, called
rarefaction.

Think of a slinky pressed together (compressions) and

Sound waves have different parts. The top of a sound wave is called
the
crest,
the bottom of a so
und wave is called the
trough,

and the
distance between two side by side crests is called the
wavelength.

When an object vibrates very quickly, the number of vibrations per
minute increase and the sound becomes higher. When this same object
vibrates more s
lowly, the number of vibrations per minute decrease,
and the sound becomes lower.

The frequency

of sound is the number of wavelengths in a given unit
of time
.

The highness and lowness of a sound wave is its
pitch.

Pitch is
determined by the frequency of a
vibrating object. Objects vibrating
faster have a higher pitch than objects vibrating slower.

Longer, larger objects (trombone) tend to vibrate slower than
shorter, smaller objects (flute).

Amplitude is the amount of energy in a compression (longitudinal)

wave
and is related to intensity and volume. For example, when a loud sound
is heard, it is because many molecules have been vibrated with much
force. A soft sound is made with fewer molecules being vibrated with
less force.

The speed of a sound depends o
n the kind of matter it is moving
through.

Of the three states of matter (gas, liquid, and solid) sound waves
travel the slowest through gases, faster through liquids, and fastest
through solids.

In a gas the molecules are spaced very far apart. For sound
to travel
through air, the floating molecules of matter must vibrate and collide
to form compression waves. Because the molecules of matter in a gas
are spaced far apart, sound does not move very quickly through them.

Sound travels faster in liquids than i
n gases because molecules are
packed more closely together. This means that when the water
molecules begin to vibrate they quickly begin to collide with each
other forming a rapidly moving compression wave. Sound travels over
four times faster than in air
!

Sound travels fastest through solids. This is because molecules in a
solid are packed against each other. When a vibration begins, the
molecules of a solid immediately collide and the compression wave
travels rapidly. How rapidly, you ask? Sound waves
travel over 17
times faster through steel than through air.

As humans, we move air from our lungs across our vocal chords to
produce sound waves. These sound waves create the sound we know as
the human voice. Many animals like dogs and bats also create
sounds
in this way. However, marine mammals like whales pass air through air
sacks located in their heads to create sounds.

Hearing is the detection of sound.

Sonar

is a type of device used to detect sound. Ships use sonar to
help them navigate their ves
sels, explore underwater areas of the
ocean, and to find food.

Some animals, such as bats and whales, used echolocation to help them
find food, or even to escape predators.

All animals detect sound differently because different animals are
able to hear di
fferent frequencies of sound.

As humans, our hearing is adapted to hear best the sounds we use
every day.

Because animals can hear sounds at different frequencies, some
animals can hear sounds that humans can’t.