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.