#### Transcript Sound

```Sound
1
Sound Waves
Sound waves travel as
compression waves.
Another name for
compression waves is
longitudinal waves
2
Factors affecting speed of sound
Temperature – Sound moves
through hot air faster than cold
air due to the increased speed of
the particles.
Type of medium – Sound moves
well through dense material and
material that returns quickly to
its original position.
3
Factors affecting speed of sound
Thus, sound moves fastest in a solid
and slowest in a gas
Sound travels more quickly through
solids and liquids because the
individual molecules are closer
together than the molecules in gas
Sound waves CANNOT move
through a vacuum – they need a
medium!
4
Bells in a bell jar…
5
Decibels
The decibel (dB) is the unit
used to measure sound
intensity or loudness.
Loudness corresponds to
the amplitude of a wave.
6
Decibels
Sounds greater than 120 dB
can cause pain in human ears.
Sounds with an amplitude
between 0 dB and 120 dB are
called audible.
Anything below 0 dB is
considered subaudible.
7
Decibel drag races
8
Frequency and Pitch
Pitch – how high or low a
sound is.
High pitch = high frequency
Low pitch = low frequency
9
Frequency and Pitch
Humans can hear pitches that
have a frequency between 20
Hz and 20,000 Hz
Pitches above 20,000 Hz are
called ultrasonic.
Pitches below 20 Hz are called
subsonic.
10
Phone Tone Generators
11
Doppler Effect
The Doppler effect is a change in
the frequency or pitch of a sound
that is caused by either the
movement of the source or the
observer of the wave.
Example: The sound from an
ambulance siren changes as it
approaches the listener
12
Doppler Effect
First observed in 1842 by
Christian Andreas Doppler
The Big Bang Theory - Doppler Costume
Video explaining the Physics of the Doppler Effect
13
Resonance
Resonance is the vibration of
an object at its natural
frequency.
Example: Windows rattle
when the sound from a passing
truck matches the window’s
natural resonance.
14
Resonance of different things
15
Nodes and Anti-nodes
Node – A place
where two waves
meet and
destructively
interfere so that the
displacement is zero
16
Nodes and Anti-nodes
Anti-node – the
point of largest
amplitude when
two waves
interfere
constructively
17
Music – Natural Frequency
A natural frequency exists
without any driving source.
It is a natural frequency if its
waveform has nodes that match
up with the ends of the object.
The lowest frequency at which
this occurs is the fundamental, or
the 1st Harmonic.
18
Music - Harmonics
Harmonics – a sound wave with a
pitch that is a multiple of the
natural frequency
Overtone – has a higher
frequency than the fundamental
Octave = ½ or double the
frequency of a sound; 8 notes on
the musical scale
19
20
Music
Consonance – multiple waves
combining to form a pleasant sound
Dissonance – multiple waves
combining to form an unpleasant
sound
Acoustics – the control of noise and
the vibrations that cause noise
21
Toccata Fugue in D Minor
22
Music – open pipe resonators
Open pipe resonators – both
ends are open
Examples: brass instruments,
flutes, saxophones
It reflects an inverted wave
23
Music - Closed pipe resonators
Closed pipe resonators –
have one end enclosed
Example: pan-flute,
blowing across a bottle top,
hanging pipes under
marimbas, xylophones
24
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