Sound waves
are longitudinal waves produced by variations in air pressure. A vibrating source pushes molecules in air back and forth, creating areas of compression and rarefaction. When a molecule moves, it collides with the next one and makes it move too. The energy of a sound wave travels away from the source trough a series of molecule collisions parallel to the direction of the wave. Sound cannot travel th
rarefaction compression
Sound waves can also travel trough liquids and solids. The velocity of a sound wave depends on the temperature of the medium and its elasticity (more elasticity means that molecules will move easily). Through air, sound waves travel at 343 m/s. Actually, sound waves move faster through liquids and solids than through gases.
Measuring sound waves
The frequency of a sound wave is called pitch. In music, different pitches (C, D, E, etc.) are represented by notes.
You need a Java-enabled browser to view this Applet
The human ear is able to feel frequencies between 20 Hz to 15 000 Hz, depending on the age of the person. Sound waves with a frequency above 20 000 Hz are called ultrasonic waves.
The amplitude or volume of a sound wave is the amount of pressure exerted by a sound source to air molecules. The higher the pressure, the harder the molecules will collide and the farther the wave will travel.
You need a Java-enabled browser
Scientists measure the amplitude in atmospheres. Humans can detect from less than a billionth of an atmosphere to values one million times higher. However, it is hard to deal with this huge range of different values. Instead, the pressure is measured by the intensity of the sound. The quietest sound corresponds to a value of zero decibels (unit of sound intensity) and a value above a hundred corresponds to annoying sounds.
Example:
A sound wave with a wavelength of 1.24 m is moving at 343 m/s. What is the
frequency of this wave?
wl = wavelength
wl = 1.24 m
v = 343 m/s
v = (wl)f
f = v/wl = (343 m/s)/(1.24 m) = 276.61 Hz
are longitudinal waves produced by variations in air pressure. A vibrating source pushes molecules in air back and forth, creating areas of compression and rarefaction. When a molecule moves, it collides with the next one and makes it move too. The energy of a sound wave travels away from the source trough a series of molecule collisions parallel to the direction of the wave. Sound cannot travel th
rarefaction compression
Sound waves can also travel trough liquids and solids. The velocity of a sound wave depends on the temperature of the medium and its elasticity (more elasticity means that molecules will move easily). Through air, sound waves travel at 343 m/s. Actually, sound waves move faster through liquids and solids than through gases.
Measuring sound waves
The frequency of a sound wave is called pitch. In music, different pitches (C, D, E, etc.) are represented by notes.
You need a Java-enabled browser to view this Applet
The human ear is able to feel frequencies between 20 Hz to 15 000 Hz, depending on the age of the person. Sound waves with a frequency above 20 000 Hz are called ultrasonic waves.
The amplitude or volume of a sound wave is the amount of pressure exerted by a sound source to air molecules. The higher the pressure, the harder the molecules will collide and the farther the wave will travel.
You need a Java-enabled browser
Scientists measure the amplitude in atmospheres. Humans can detect from less than a billionth of an atmosphere to values one million times higher. However, it is hard to deal with this huge range of different values. Instead, the pressure is measured by the intensity of the sound. The quietest sound corresponds to a value of zero decibels (unit of sound intensity) and a value above a hundred corresponds to annoying sounds.
Example:
A sound wave with a wavelength of 1.24 m is moving at 343 m/s. What is the
frequency of this wave?
wl = wavelength
wl = 1.24 m
v = 343 m/s
v = (wl)f
f = v/wl = (343 m/s)/(1.24 m) = 276.61 Hz
