Sound is vibration transmitted through a solid, liquid, or gas; particularly, sound means those vibrations composed of
frequencies capable of being detected by ears.
Perception of sound
Human earFor humans, hearing is limited to frequencies between about 20 Hz and 20,000 Hz (20 kHz), with the upper
limit generally decreasing with age. Other species have a different range of hearing. For example, dogs can perceive
vibrations higher than 20 kHz. As a signal perceived by one of the major senses, sound is used by many species for
detecting danger, navigation, predation, and communication. Earth's atmosphere, water, and virtually any physical
phenomenon, such as fire, rain, wind, surf, or earthquake, produces (and is characterized by) its unique sounds. Many
species, such as frogs, birds, marine and terrestrial mammals, have also developed special organs to produce sound.
In some species, these have evolved to produce song and speech. Furthermore, humans have developed culture and
technology (such as music, telephone and radio) that allows them to generate, record, transmit, and broadcast sound.
Physics of sound
The mechanical vibrations that can be interpreted as sound are able to travel through all forms of matter: gases, liquids,
solids, and plasmas. The matter that supports the sound is called the medium. Sound cannot travel through vacuum.
Longitudinal and transverse waves
Sinusoidal waves of various frequencies; the bottom waves have higher frequencies than those above. The horizontal
axis represents time.Sound is transmitted through gases, plasma, and liquids as longitudinal waves, also called
compression waves. Through solids, however, it can be transmitted as both longitudinal and transverse waves.
Longitudinal sound waves are waves of alternating pressure deviations from the equilibrium pressure, causing local
regions of compression and rarefaction, while transverse waves in solids, are waves of alternating shear stress.
Matter in the medium is periodically displaced by a sound wave, and thus oscillates. The energy carried by the sound
wave converts back and forth between the potential energy of the extra compression (in case of longitudinal waves) or
lateral displacement strain (in case of transverse waves) of the matter and the kinetic energy of the oscillations of the
Sound wave properties and characteristics
Sound waves are characterized by the generic properties of waves, which are frequency, wavelength, period, amplitude,
intensity, speed, and direction (sometimes speed and direction are combined as a velocity vector, or wavelength and
direction are combined as a wave vector).
Transverse waves, also known as shear waves, have an additional property of polarization.
Sound characteristics can depend on the type of sound waves (longitudinal versus transverse) as well as on the
physical properties of the transmission medium.
Whenever the pitch of the soundwave is affected by some kind of change, the distance between the sound wave maxima
also changes, resulting in a change of frequency. When the loudness of a soundwave changes, so does the amount of
compression in airwave that is travelling through it, which in turn can be defined as amplitude.
Speed of sound
(stiffness) of the medium to its density. Those physical properties and the speed of (stiffness) of the medium to its
density. Those physical properties and the speed of sound change with ambient conditions. For example, the speed of
sound in gases depends on temperature. In 20°C (68°F) air at sea level, the speed of sound is approximately 343 m/s
(767.3 mph). In fresh water, also at 20°C, the speed of sound is approximately 1482 m/s (3,315.1 mph). In steel the
speed of sound is about 5960 m/s (13,332.1 mph). The speed of sound is also slightly sensitive (a second-order
effect) to the sound amplitude, which means that there are nonlinear propagation effects, such as the production of
harmonics and mixed tones not present in the original sound (see parametric array).
original sound (see parametric array).
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