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{{Short description|Physical process by which an object is held aloft, without mechanical support, in a stable position}}
] levitating over a ] material.]]
{{other uses|Levitation (disambiguation)}}
{{more footnotes needed|date=March 2017}}
] levitating over a ] material (known as the ])]]
'''Levitation''' (from ] ''{{linktext|levitas}}'', {{literal|lightness}})<ref>''Levitate'', "to rise by virtue of lightness," from Latin ''levitas'' "lightness," patterned in English on ''gravitate'': </ref> is the process by which an object is held aloft in a stable position, without mechanical support via any physical contact.


Levitation is accomplished by providing an upward ] that counteracts the pull of ] (in relation to gravity on earth), plus a smaller stabilizing force that pushes the object toward a home position whenever it is a small distance away from that home position. The force can be a fundamental force such as magnetic or electrostatic, or it can be a reactive force such as optical, buoyant, aerodynamic, or hydrodynamic.{{Citation needed|date=December 2014}}
'''Levitation''' (from ] ''levis'', light) is the process by which an object is suspended against ], in a stable position, by a ] without ].
Levitation excludes ] at the surface of a liquid because the liquid provides direct mechanical support. Levitation excludes hovering flight by insects, hummingbirds, helicopters, rockets, and balloons because the object provides its own counter-gravity force.{{Citation needed|date=December 2014}}


==Physics==
Western science acknowledges that this can be achieved through jets of gas pushing upwards against the object (as in ]), or pushing downwards from the object (as in ]s, ] aircraft, and ]), while levitation is also a part of some eastern religions and magical beliefs.
Levitation (on ] or any planetoid) requires an upward force that cancels out the ] of the object, so that the object does not fall (accelerate downward) or rise (accelerate upward). For positional stability, any small displacement of the levitating object must result in a small change in force in the opposite direction.{{Citation needed|date=December 2014}} the small changes in force can be accomplished by gradient field(s) or by active regulation. If the object is disturbed, it might oscillate around its final position, but its motion eventually decreases to zero due to ] effects. (In a turbulent flow, the object might oscillate indefinitely.){{Citation needed|date=December 2014}}


Levitation techniques are useful tools in physics research. For example, levitation methods are useful for high-temperature melt property studies because they eliminate the problem of reaction with containers and allow deep undercooling of melts. The containerless conditions may be obtained by opposing gravity with a levitation force instead of allowing an entire experiment to freefall.<ref name=Nordine2000>{{citation|author1=Paul C. Nordine |author2=J. K. Richard Weber |author3=Johan G. Abadie |journal=Pure and Applied Chemistry|title=Properties of high-temperature melts using levitation|date=2000|volume=72|issue=11 |pages=2127–2136|doi=10.1351/pac200072112127|doi-access=free}}</ref>
A sphere can be stably levitated in a stream of air without any type of control system, if conditions are right. These effects are due to ]. This was merchandised as a toy, circa ].


==Magnetic levitation==
Objects with the right properties can be levitated without even indirect contact through the use of ] or ]s. Technically, we are in a state of constant levitation, since our body exerts a force on physical bodies and they exert one in return (], the third one). So our bodies never actually come into contact with another object.
{{main|Magnetic levitation}}


] levitating above magnet]]
Some claim there are other ways - using methods not yet known to modern ] - to levitate objects. These may include ] or ]-related methods of raising an object off the ground. Perhaps the most stereotypically famous example is of monks and/or religious people that live a ] life levitating at will, a today-common element, almost a ], in ] involving monks. It is said that the Christian theologian ] was seen levitating after a mystical experience. The numerous stories involving religious or religion-related or induced levitation suggest that "true" or unaided (by apparent, or, at least, earthly ]) levitation may be a divine act or consequence of a divine revelation.


Magnetic levitation is the most commonly seen and used form of levitation. This form of levitation occurs when an object is suspended using magnetic fields.
"Levitation" is also used in reference to an apparent levitation.


] materials are commonly used for demonstration purposes. In this case the returning force appears from the interaction with the ]s. For example, a ] sample, which can be considered either as a perfect diamagnet or an ], easily levitates in an ambient external magnetic field. The superconductor is cooled with liquid nitrogen to levitate on top of a magnet becoming super diamagnetic. In a powerful magnetic field utilizing ], even small live animals have been levitated.
The original use of the word was to refer to such inexplicable claims, as in wonder stories and unauthenticated reports; the use of the word to describe an actual, physical means of "making things float in the air" is a recent development.


It is possible to levitate pyrolytic graphite by placing thin squares of it above four cube magnets with the north poles forming one diagonal and south poles forming the other diagonal.<ref>{{citation|author=Waldron, Robert D.|title=Diamagnetic Levitation Using Pyrolytic Graphite|journal=Review of Scientific Instruments|volume=37|issue=1|pages=29–35|doi=10.1063/1.1719946|bibcode = 1966RScI...37...29W |year=1966|doi-access=free}}</ref> Researchers have even successfully levitated (non-magnetic) liquid droplets surrounded by paramagnetic fluids.<ref>{{citation|author=Singh, Chamkor|author2=Das, Arup K.|author3=Das, Prasanta K.|title=Levitation of non-magnetizable droplet inside ferrofluid|journal=Journal of Fluid Mechanics|year=2018|volume=857|pages=398–448|doi=10.1017/jfm.2018.733|url=https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/levitation-of-nonmagnetizable-droplet-inside-ferrofluid/DD631FF653EE08399CBB233301E381D5#|arxiv=1712.01500|bibcode=2018JFM...857..398S|s2cid=53607312}}</ref> The process of such inverse magnetic levitation is usually referred to as Magneto-Archimedes effect.
{{physics-stub}}


] on the first commercial high-speed maglev line in the world.]]
== See Also ==


Magnetic levitation is in development for use for transportation systems. For example, the ] includes trains that are levitated by a large number of magnets. Due to the lack of friction on the guide rails, they are faster, quieter, and smoother than wheeled mass transit systems.
* ] Effects
** ] (rail systems etc)
** ]
* Magic Illusions
** ]
** ]
** ]
** ]
** ]
** ]
** ]
** ]
** ]
** ]/]
* ]s
** ]
** ]
** ]
** ]
* Other
* ] (by means not known to modern science, such as ] and the ])
* ] is also the name of a band.


] uses AC magnetic fields.
]
]
]
]
]
]
]


==Electrostatic levitation==
]
{{main|Electrostatic levitation}}
]
In electrostatic levitation an ] is used to counteract gravitational force. Some spiders shoot silk into the air to ride Earth's electric field.

==Aerodynamic levitation==
{{main|Aerodynamic levitation}}
In aerodynamic levitation, the levitation is achieved by floating the object on a stream of gas, either produced by the object or acting on the object. For example, a ] can be levitated with the stream of air from a vacuum cleaner set on "blow" - exploiting the ] which keeps it stable in the airstream. With enough thrust, very large objects can be levitated using this method.

===Gas film levitation===
This technique enables the levitation of an object against ] by floating it on a thin ] film formed by gas flow through a ] membrane. Using this technique, high temperature melts can be kept clean from contamination and be supercooled.<ref name=Nordine2000/> A common example in general usage includes ], where the puck is lifted by a thin layer of air. ] also use this technique, producing a large region of high-pressure air underneath them.

==Acoustic levitation==
{{main|Acoustic levitation}}
Acoustic levitation uses sound waves to provide a levitating force.

==Optical levitation==
{{main|Optical levitation}}
Optical levitation is a technique in which a material is levitated against the downward force of gravity by an upward force stemming from ] ] transfer (]).

==Buoyant levitation==<!-- ] redirects here. -->
Gases at high pressure can have a density exceeding that of some solids. Thus they can be used to levitate solid objects through ].<ref>http://www.mrs.org/s_mrs/sec_subscribe.asp?CID=12048&DID=275340&action=detail Materials Processing Through Levitation in High Gas Pressure</ref> ]es are preferred for their non-reactivity. ] is the densest non-radioactive noble gas, at 5.894g/L. Xenon has been used to levitate ], at a pressure of 154atm.

==Casimir force==
Scientists have discovered a way of levitating ultra small objects by manipulating the ], which normally causes objects to stick together due to forces predicted by ]. This is, however, only possible for micro-objects.<ref>{{cite web|url=https://news.yahoo.com/s/afp/20070806/sc_afp/britainsciencelevitation_070806132733|title=Scientists reveal secret of levitation, Yahoo! News|website=yahoo.com}}</ref><ref>{{cite web|url=http://www.null-hypothesis.co.uk/science/news/item/levitation_magic_nanotechnology_particles_research|title=Levitation in Miniature, Null Hypothesis|website=null-hypothesis.co.uk|access-date=2007-08-23|archive-url=https://web.archive.org/web/20110717123841/http://www.null-hypothesis.co.uk/science/news/item/levitation_magic_nanotechnology_particles_research|archive-date=2011-07-17|url-status=dead}}</ref>

==Uses==

===Maglev trains===
{{main|Maglev}}
Magnetic levitation is used to suspend trains without touching the track. This permits very high speeds, and greatly reduces the maintenance requirements for tracks and vehicles, as little wear occurs. This also means there is no friction, so the only force acting against it is air resistance.

===Animal levitation===
] levitation of a live frog.]]
Scientists have levitated frogs,<ref>{{cite web|title=Frogs Levitate in a strong enough magnetic field|url=http://www.physics.org/facts/frog-really.asp|publisher=physics.org|access-date=20 November 2014}}</ref> grasshoppers, and mice by means of powerful electromagnets utilizing superconductors, producing ] repulsion of body water. The mice acted confused at first, but adapted to the levitation after approximately four hours, suffering no immediate ill effects.<ref>{{cite journal|title=NASA Levitates a Mouse With Magnetic Fields|journal=Popular Science|date=September 9, 2009|url=http://www.popsci.com/scitech/article/2009-09/nasa-levitates-mouse|access-date=20 November 2014}}</ref><ref> Mice Levitated in Lab</ref>

==Further reading==
*{{cite journal |author1=Charles P. Strehlow |author2=M. C. Sullivan |title=A Classroom Demonstration of Levitation... |journal=American Journal of Physics |volume=77 |issue=9 |pages=847–851 |date=2008 |arxiv=0803.3090|doi=10.1119/1.3095809 |s2cid=119108808 }}.

==See also==
*]
*]
*]
*]
*]
*]
*]

==References==
{{reflist}}

==External links==
*{{wiktionary-inline}}
*
*

{{Authority control}}

]
]

Latest revision as of 20:39, 10 May 2024

Physical process by which an object is held aloft, without mechanical support, in a stable position For other uses, see Levitation (disambiguation).
This article includes a list of general references, but it lacks sufficient corresponding inline citations. Please help to improve this article by introducing more precise citations. (March 2017) (Learn how and when to remove this message)
A cube magnet levitating over a superconducting material (known as the Meissner effect)

Levitation (from Latin levitas, lit. 'lightness') is the process by which an object is held aloft in a stable position, without mechanical support via any physical contact.

Levitation is accomplished by providing an upward force that counteracts the pull of gravity (in relation to gravity on earth), plus a smaller stabilizing force that pushes the object toward a home position whenever it is a small distance away from that home position. The force can be a fundamental force such as magnetic or electrostatic, or it can be a reactive force such as optical, buoyant, aerodynamic, or hydrodynamic. Levitation excludes floating at the surface of a liquid because the liquid provides direct mechanical support. Levitation excludes hovering flight by insects, hummingbirds, helicopters, rockets, and balloons because the object provides its own counter-gravity force.

Physics

Levitation (on Earth or any planetoid) requires an upward force that cancels out the weight of the object, so that the object does not fall (accelerate downward) or rise (accelerate upward). For positional stability, any small displacement of the levitating object must result in a small change in force in the opposite direction. the small changes in force can be accomplished by gradient field(s) or by active regulation. If the object is disturbed, it might oscillate around its final position, but its motion eventually decreases to zero due to damping effects. (In a turbulent flow, the object might oscillate indefinitely.)

Levitation techniques are useful tools in physics research. For example, levitation methods are useful for high-temperature melt property studies because they eliminate the problem of reaction with containers and allow deep undercooling of melts. The containerless conditions may be obtained by opposing gravity with a levitation force instead of allowing an entire experiment to freefall.

Magnetic levitation

Main article: Magnetic levitation
a high-temperature superconductor levitating above magnet

Magnetic levitation is the most commonly seen and used form of levitation. This form of levitation occurs when an object is suspended using magnetic fields.

Diamagnetic materials are commonly used for demonstration purposes. In this case the returning force appears from the interaction with the screening currents. For example, a superconducting sample, which can be considered either as a perfect diamagnet or an ideally hard superconductor, easily levitates in an ambient external magnetic field. The superconductor is cooled with liquid nitrogen to levitate on top of a magnet becoming super diamagnetic. In a powerful magnetic field utilizing diamagnetic levitation, even small live animals have been levitated.

It is possible to levitate pyrolytic graphite by placing thin squares of it above four cube magnets with the north poles forming one diagonal and south poles forming the other diagonal. Researchers have even successfully levitated (non-magnetic) liquid droplets surrounded by paramagnetic fluids. The process of such inverse magnetic levitation is usually referred to as Magneto-Archimedes effect.

A magnetically levitated (maglev) train departing Shanghai Pudong International Airport on the first commercial high-speed maglev line in the world.

Magnetic levitation is in development for use for transportation systems. For example, the Maglev includes trains that are levitated by a large number of magnets. Due to the lack of friction on the guide rails, they are faster, quieter, and smoother than wheeled mass transit systems.

Electrodynamic suspension uses AC magnetic fields.

Electrostatic levitation

Main article: Electrostatic levitation

In electrostatic levitation an electric field is used to counteract gravitational force. Some spiders shoot silk into the air to ride Earth's electric field.

Aerodynamic levitation

Main article: Aerodynamic levitation

In aerodynamic levitation, the levitation is achieved by floating the object on a stream of gas, either produced by the object or acting on the object. For example, a ping pong ball can be levitated with the stream of air from a vacuum cleaner set on "blow" - exploiting the Coandă effect which keeps it stable in the airstream. With enough thrust, very large objects can be levitated using this method.

Gas film levitation

This technique enables the levitation of an object against gravitational force by floating it on a thin gas film formed by gas flow through a porous membrane. Using this technique, high temperature melts can be kept clean from contamination and be supercooled. A common example in general usage includes air hockey, where the puck is lifted by a thin layer of air. Hovercraft also use this technique, producing a large region of high-pressure air underneath them.

Acoustic levitation

Main article: Acoustic levitation

Acoustic levitation uses sound waves to provide a levitating force.

Optical levitation

Main article: Optical levitation

Optical levitation is a technique in which a material is levitated against the downward force of gravity by an upward force stemming from photon momentum transfer (radiation pressure).

Buoyant levitation

Gases at high pressure can have a density exceeding that of some solids. Thus they can be used to levitate solid objects through buoyancy. Noble gases are preferred for their non-reactivity. Xenon is the densest non-radioactive noble gas, at 5.894g/L. Xenon has been used to levitate polyethylene, at a pressure of 154atm.

Casimir force

Scientists have discovered a way of levitating ultra small objects by manipulating the Casimir force, which normally causes objects to stick together due to forces predicted by quantum field theory. This is, however, only possible for micro-objects.

Uses

Maglev trains

Main article: Maglev

Magnetic levitation is used to suspend trains without touching the track. This permits very high speeds, and greatly reduces the maintenance requirements for tracks and vehicles, as little wear occurs. This also means there is no friction, so the only force acting against it is air resistance.

Animal levitation

Diamagnetic levitation of a live frog.

Scientists have levitated frogs, grasshoppers, and mice by means of powerful electromagnets utilizing superconductors, producing diamagnetic repulsion of body water. The mice acted confused at first, but adapted to the levitation after approximately four hours, suffering no immediate ill effects.

Further reading

See also

References

  1. Levitate, "to rise by virtue of lightness," from Latin levitas "lightness," patterned in English on gravitate: Online Etymology Dictionary
  2. ^ Paul C. Nordine; J. K. Richard Weber; Johan G. Abadie (2000), "Properties of high-temperature melts using levitation", Pure and Applied Chemistry, 72 (11): 2127–2136, doi:10.1351/pac200072112127
  3. Waldron, Robert D. (1966), "Diamagnetic Levitation Using Pyrolytic Graphite", Review of Scientific Instruments, 37 (1): 29–35, Bibcode:1966RScI...37...29W, doi:10.1063/1.1719946
  4. Singh, Chamkor; Das, Arup K.; Das, Prasanta K. (2018), "Levitation of non-magnetizable droplet inside ferrofluid", Journal of Fluid Mechanics, 857: 398–448, arXiv:1712.01500, Bibcode:2018JFM...857..398S, doi:10.1017/jfm.2018.733, S2CID 53607312
  5. http://www.mrs.org/s_mrs/sec_subscribe.asp?CID=12048&DID=275340&action=detail Materials Processing Through Levitation in High Gas Pressure
  6. "Scientists reveal secret of levitation, Yahoo! News". yahoo.com.
  7. "Levitation in Miniature, Null Hypothesis". null-hypothesis.co.uk. Archived from the original on 2011-07-17. Retrieved 2007-08-23.
  8. "Frogs Levitate in a strong enough magnetic field". physics.org. Retrieved 20 November 2014.
  9. "NASA Levitates a Mouse With Magnetic Fields". Popular Science. September 9, 2009. Retrieved 20 November 2014.
  10. Mice Levitated in Lab

External links

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