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Acoustics is a branch of physics that deals with the study of mechanical waves in gases, liquids, and solids including topics such as vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics technology may be called an acoustical engineer. The application of acoustics is present in almost all aspects of modern society with the most obvious being the audio and noise control industries.
The Mach number, often only Mach, is a dimensionless quantity in fluid dynamics representing the ratio of flow velocity past a boundary to the local speed of sound. It is named after the Czech physicist and philosopher Ernst Mach.
Seneca Lake is the largest of the glacial Finger Lakes of the U.S. state of New York, and the deepest glacial lake entirely within the state. It is promoted as the lake trout capital of the world, and is host of the National Lake Trout Derby. Because of its depth and relative ease of access, the US Navy uses Seneca Lake to perform test and evaluation of equipment ranging from single element transducers to complex sonar arrays and systems. The lake takes its name from the Seneca nation of Native Americans. At the north end of Seneca Lake is the city of Geneva, New York, home of Hobart and William Smith Colleges and the New York State Agricultural Experiment Station, a division of Cornell University. At the south end of the lake is the village of Watkins Glen, New York, famed for auto racing and waterfalls.
The Tunguska event was a large explosion of between 3 and 50 megatons that occurred near the Podkamennaya Tunguska River in Yeniseysk Governorate, Russia, on the morning of 30 June 1908. The explosion over the sparsely populated East Siberian taiga flattened an estimated 80 million trees over an area of 2,150 km2 (830 sq mi) of forest, and eyewitness accounts suggest up to three people may have died. The explosion is generally attributed to a meteor air burst, the atmospheric explosion of a stony asteroid about 50–60 metres wide. The asteroid approached from the east-south-east, probably with a relatively high speed of about 27 km/s (60,000 mph). Though the incident is classified as an impact event, the object is thought to have exploded at an altitude of 5 to 10 kilometres rather than hitting the Earth's surface, leaving no impact crater.
Atmospheric entry is the movement of an object from outer space into and through the gases of an atmosphere of a planet, dwarf planet, or natural satellite. There are two main types of atmospheric entry: uncontrolled entry, such as the entry of astronomical objects, space debris, or bolides; and controlled entry of a spacecraft capable of being navigated or following a predetermined course. Technologies and procedures allowing the controlled atmospheric entry, descent, and landing of spacecraft are collectively termed as EDL.
The thermosphere is the layer in the Earth's atmosphere directly above the mesosphere and below the exosphere. Within this layer of the atmosphere, ultraviolet radiation causes photoionization/photodissociation of molecules, creating ions; the thermosphere thus constitutes the larger part of the ionosphere. Taking its name from the Greek θερμός meaning heat, the thermosphere begins at about 80 km (50 mi) above sea level. At these high altitudes, the residual atmospheric gases sort into strata according to molecular mass. Thermospheric temperatures increase with altitude due to absorption of highly energetic solar radiation. Temperatures are highly dependent on solar activity, and can rise to 2,000 °C (3,630 °F) or more. Radiation causes the atmospheric particles in this layer to become electrically charged, enabling radio waves to be refracted and thus be received beyond the horizon. In the exosphere, beginning at about 600 km (375 mi) above sea level, the atmosphere turns into space, although, by the judging criteria set for the definition of the Kármán line (100 km), most of the thermosphere is part of space. The border between the thermosphere and exosphere is known as the thermopause.
Supersonic speed is the speed of an object that exceeds the speed of sound (Mach 1). For objects traveling in dry air of a temperature of 20 °C (68 °F) at sea level, this speed is approximately 343.2 m/s. Speeds greater than five times the speed of sound (Mach 5) are often referred to as hypersonic. Flights during which only some parts of the air surrounding an object, such as the ends of rotor blades, reach supersonic speeds are called transonic. This occurs typically somewhere between Mach 0.8 and Mach 1.2.
A meteoroid is a small rocky or metallic body in outer space. Meteoroids are distinguished as objects significantly smaller than asteroids, ranging in size from grains to objects up to a meter wide. Objects smaller than meteoroids are classified as micrometeoroids or space dust. Many are fragments from comets or asteroids, whereas others are collision impact debris ejected from bodies such as the Moon or Mars.
In physics, a shock wave, or shock, is a type of propagating disturbance that moves faster than the local speed of sound in the medium. Like an ordinary wave, a shock wave carries energy and can propagate through a medium but is characterized by an abrupt, nearly discontinuous, change in pressure, temperature, and density of the medium.
The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elastic medium. At 20 °C (68 °F), the speed of sound in air is about 343 m/s, or 1 km in 2.91 s or one mile in 4.69 s. It depends strongly on temperature as well as the medium through which a sound wave is propagating. At 0 °C (32 °F), the speed of sound in air is about 331 m/s. More simply, the speed of sound is how fast vibrations travel.
A sonic boom is a sound associated with shock waves created when an object travels through the air faster than the speed of sound. Sonic booms generate enormous amounts of sound energy, sounding similar to an explosion or a thunderclap to the human ear.
Singing sand, also called whistling sand, barking sand or singing dune, is sand that produces sound. The sound emission may be caused by wind passing over dunes or by walking on the sand.
Infrasound, sometimes referred to as low frequency sound, describes sound waves with a frequency below the lower limit of human audibility. Hearing becomes gradually less sensitive as frequency decreases, so for humans to perceive infrasound, the sound pressure must be sufficiently high. Although the ear is the primary organ for sensing low sound, at higher intensities it is possible to feel infrasound vibrations in various parts of the body.
Atmospheric focusing is a type of wave interaction causing shock waves to affect areas at a greater distance than otherwise expected. Variations in the atmosphere create distortions in the wavefront by refracting a segment, allowing it to converge at certain points and constructively interfere. In the case of destructive shock waves, this may result in areas of damage far beyond the theoretical extent of its blast effect. Examples of this are seen during supersonic booms, large extraterrestrial impacts from objects like meteors, and nuclear explosions.
Barisal guns or fog guns are a series of loud booms heard near the Barisal region of East Bengal in the 19th century. There are various theories about the origin of the sound. One common explanation is that it was caused by the sound of waves, broken up by local topography, but geological origins have also been proposed. The sound is an example of a skyquake – an unexplained sudden loud sound without corresponding earthquake activity. Similar sounds have been reported in many waterfront communities around the world such as the Ganges Delta and Brahmaputra River delta in Bangladesh, the East Coast and inland Finger Lakes of the United States, as well as areas of the North Sea, the lakes of southern Germany, Japan and Italy; and sometimes away from water, for example, in the American midwest where they have been attributed to cold temperature.
In physics, sound is a vibration that propagates as an acoustic wave through a transmission medium such as a gas, liquid or solid. In human physiology and psychology, sound is the reception of such waves and their perception by the brain. Only acoustic waves that have frequencies lying between about 20 Hz and 20 kHz, the audio frequency range, elicit an auditory percept in humans. In air at atmospheric pressure, these represent sound waves with wavelengths of 17 meters (56 ft) to 1.7 centimeters (0.67 in). Sound waves above 20 kHz are known as ultrasound and are not audible to humans. Sound waves below 20 Hz are known as infrasound. Different animal species have varying hearing ranges.
A tsunami is a series of water waves caused by the displacement of a large volume within a body of water, often caused by earthquakes, or similar events. This may occur in lakes as well as oceans, presenting threats to both fishermen and shoreside inhabitants. Because they are generated by a near field source region, tsunamis generated in lakes and reservoirs result in a decreased amount of warning time.
A meteor air burst is a type of air burst in which a meteoroid explodes after entering a planetary body's atmosphere. This fate leads them to be called fireballs or bolides, with the brightest air bursts known as superbolides. Such meteoroids were originally asteroids and comets of a few to several tens of meters in diameter. This separates them from the much smaller and far more common "shooting stars", that usually burn up quickly upon atmospheric entry.
References
- ↑ T.D. LaTouche, "On the Sounds Known as Barisal Guns", Report (1890-8) of the annual meeting By British Association for the Advancement of Science, Issue 60, pp. 800.
- ↑ Eraldo Baldini, "Tenebrosa Romagna", Il Ponte Vecchio, 2014, p. 21.
- ↑ William R. Corliss, Earthquakes, Tides, Unidentified Sounds, and related phenomena (The Sourcebook Project, 1983).
- ↑ M.G.J.Minnaert, De Natuurkunde van 't Vrije Veld, Deel 2: Geluid, Warmte, Elektriciteit, § 48: Mistpoeffers, bladzijden 63-64.
- ↑ Appletons' Annual Cyclopaedia and Register of Important Events. 1899. p. 440.
- 1 2 Earthquake Booms, Seneca Guns, and Other Sounds, usgs.gov, 2013-10-29
- ↑ "Milkshakes: unusual earthquakes strike Wisconsin". Ars Technica. 2013-02-25. Retrieved 2013-02-25.
- ↑ Dimitar Ouzounov; Sergey Pulinets; Alexey Romanov; Alexander Romanov; Konstantin Tsybulya; Dimitri Davidenko; Menas Kafatos; Patrick Taylor (2011). "Atmosphere-Ionosphere Response to the M9 Tohoku Earthquake Revealed by Joined Satellite and Ground Observations. Preliminary results". arXiv: 1105.2841 [physics.geo-ph].
- ↑ Wilson, D. Keith; Noble, John M.; Coleman, Mark A. (2003-10-01). "Sound Propagation in the Nocturnal Boundary Layer". Journal of the Atmospheric Sciences. 60 (20): 2473–2486. doi: 10.1175/1520-0469(2003)060<2473:SPITNB>2.0.CO;2 . ISSN 0022-4928.