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4A Wave Basics Wave Measures Wave Collisions Interference Reflect,Refract, & Diffract Sound Waves Doppler Effect WaveSimulation 1 Infrasound Recording Processing Examples WaveSimulation 2 |
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| Basics of Sound Waves |
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 through
a vacuum.
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.
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.
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.
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