SOUND 24.2 Chapter Twenty-Four: Sound 24.1 Properties of Sound 24.2 Sound Waves 24.3 Sound Perception and Music.
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Transcript SOUND 24.2 Chapter Twenty-Four: Sound 24.1 Properties of Sound 24.2 Sound Waves 24.3 Sound Perception and Music.
SOUND 24.2
Chapter Twenty-Four: Sound
24.1 Properties of Sound
24.2 Sound Waves
24.3 Sound Perception and
Music
Chapter 24.2 Learning Goals
Justify the classification of sound
as a wave.
Analyze sound interactions at
boundaries.
Explain how factors like
temperature and pressure affect
the behavior of sound waves.
Investigation 24B
Resonance in Other Systems
Key Question:
How can resonance
be controled to
make the sounds
we want?
24.2 What is a sound wave?
Sound waves are pressure waves with
alternating high and low pressure regions.
When they are pushed by the vibrations, it
creates a layer of higher pressure which
results in a traveling vibration of pressure.
24.2 What is a sound wave?
At the same
temperature and
volume, higher
pressure contains
more molecules than
lower pressure.
24.2 The wavelength of sound
The wavelength of sound in air is similar
to the size of everyday objects.
24.2 The wavelength of sound
Wavelength is also
important to sound.
Musical instruments
use the wavelength
of a sound to create
different frequencies.
24.2 Standing waves
A wave that is confined in a
space is called a standing
wave.
A string with a standing
wave is a kind of oscillator.
24.2 Standing waves
The lowest natural
frequency is called
the fundamental.
A vibrating string
also has other
natural frequencies
called harmonics.
24.2 Standing waves
The place on a harmonic
with the greatest
amplitude is the antinode.
The place where the
string does not move
(least amplitude) is called
a node.
24.2 Standing waves
It is easy to measure
the wavelength of a
standing wave on a
string.
Two harmonics
equals one wave!
24.2 Standing waves in pipes
A panpipe makes music as sound
resonates in tubes of different
lengths.
The natural
frequency of
a pipe is
proportional
to its length.
24.2 Standing waves in pipes
Because frequency and
wavelength are inversely related,
longer pipes have lower natural
frequencies because they resonate
at longer wavelengths.
A pipe that must vibrate at a
frequency 2 times higher than
another pipe must be 1/2 as long.
If the long pipe has a frequency of 528 Hz,
what is the frequency of the short pipe?
24.2 Standing waves in pipes
Blowing across the open end of a tube
creates a standing wave inside the tube.
If we blow at just the right angle and we
match the natural frequency of the
material and the sound resonates
(spreads).
24.2 Standing waves in pipes
The open end of a pipe is an open
boundary to a standing wave and makes
an antinode.
The pipe resonates to a certain frequency
when its length is one-fourth the
wavelength of that frequency.
24.2 Sound wave interactions
Like other waves, sound waves can
be reflected by hard surfaces and
refracted as they pass from one
material to another.
Diffraction causes sound waves to
spread out through small openings.
Carpet and soft materials can absorb
sound waves.
24.2 Reverberation
The reflected
sound and direct
sound from the
musicians together
create a multiple
echo called
reverberation.
The right amount
of reverberation
makes the sound
seem livelier and
richer.