are the positions where the pressure is below normal.
Sound waves differ from waves on strings in that the molecules of a medium
transmitting a sound wave move parallel to the direction of wave propagation
rather than perpendicular to it.
Intensity and decibel level measure the loudness of a sound. Decibel level is
measured on a logarithmic scale.
Resonance for sound waves follows a pattern of nodes and anti-nodes. While
an open-ended tube can support any harmonic—any integer times − λ, a
closed-end tube can only support odd harmonics—an odd multiple of λ.
The Doppler effect occurs when there is relative motion between the source of
the sound waves and the detector. When the detector moves toward the source
(or vice-versa), he or she intercepts the waves at a rate higher than the one at
which they were emitted and hears a higher frequency than the source emitted.
If the detector is moving away from the source or if the source is moving away
from the detector, the detected waves have a lower frequency than originally
emitted by the source.
Light, or electromagnetic waves, also experiences the Doppler effect. Motion
toward the source corresponds to a frequency shift upward (and a wavelength
shift downward). Motion away from the source corresponds to a frequency
shift downward (and a wavelength shift upward).