Electrostatic levitation
Encyclopedia
Electrostatic levitation is the process of using an electric field
to levitate a charged
object and counteract the effects of gravity. It was used, for instance, in Robert Millikan
's oil drop experiment and is used to suspend the gyroscopes in Gravity Probe B
during launch.
Due to Earnshaw's theorem
no static arrangement of classical electrostatic fields can be used to stably levitate a point charge. There is a point where the two fields cancel, but it is unstable. By providing feedback it is possible to adjust the charges to achieve a quasi
static levitation.
Earnshaw's theorem holds that a charged particle suspended in an electrostatic field is unstable, because the forces of attraction and repulsion vary at an equal rate that is proportional to the inverse square law and remain in balance wherever a particle moves. Since the forces remain in balance, there is no inequality to provide a restoring force; and the particle remains unstable and can freely move without restriction.
On the Moon
the photoelectric effect
and electrons in the solar wind
charges fine layers of moon dust on the surface forming an atmosphere of dust floating in "fountains" over the surface of the moon.
Electric field
In physics, an electric field surrounds electrically charged particles and time-varying magnetic fields. The electric field depicts the force exerted on other electrically charged objects by the electrically charged particle the field is surrounding...
to levitate a charged
Electric charge
Electric charge is a physical property of matter that causes it to experience a force when near other electrically charged matter. Electric charge comes in two types, called positive and negative. Two positively charged substances, or objects, experience a mutual repulsive force, as do two...
object and counteract the effects of gravity. It was used, for instance, in Robert Millikan
Robert Millikan
Robert A. Millikan was an American experimental physicist, and Nobel laureate in physics for his measurement of the charge on the electron and for his work on the photoelectric effect. He served as president of Caltech from 1921 to 1945...
's oil drop experiment and is used to suspend the gyroscopes in Gravity Probe B
Gravity Probe B
Gravity Probe B is a satellite-based mission which launched on 20 April 2004 on a Delta II rocket. The spaceflight phase lasted until 2005; its aim was to measure spacetime curvature near Earth, and thereby the stress–energy tensor in and near Earth...
during launch.
Due to Earnshaw's theorem
Earnshaw's theorem
Earnshaw's theorem states that a collection of point charges cannot be maintained in a stable stationary equilibrium configuration solely by the electrostatic interaction of the charges. This was first proven by British mathematician Samuel Earnshaw in 1842. It is usually referenced to magnetic...
no static arrangement of classical electrostatic fields can be used to stably levitate a point charge. There is a point where the two fields cancel, but it is unstable. By providing feedback it is possible to adjust the charges to achieve a quasi
Quasi
Quasi is an American indie rock band formed in Portland, Oregon in 1993 by ex-husband and wife Sam Coomes and Janet Weiss . Since 2007 the group has been a trio, following the addition of bassist Joanna Bolme.-History:In 1990 , Coomes, Weiss, and Brad Pedinov formed the band Motorgoat...
static levitation.
Earnshaw's theorem
The idea of particle instability in an electrostatic field originated with Samuel Earnshaw in 1839 and was formalized by James Clerk Maxwell in 1874 who gave it the title "Earnshaw's theorem" and proved it with the Laplace equation. Earnshaw's theorem explains why a system of electrons is not stable and was invoked by Niels Bohr in his atom model of 1913 when criticizing J. J. Thomson's atom.Earnshaw's theorem holds that a charged particle suspended in an electrostatic field is unstable, because the forces of attraction and repulsion vary at an equal rate that is proportional to the inverse square law and remain in balance wherever a particle moves. Since the forces remain in balance, there is no inequality to provide a restoring force; and the particle remains unstable and can freely move without restriction.
Levitation
The first electrostatic levitator was invented by Dr. Won-Kyu Rhim at NASA's JPL lab in 1993. A charged sample of 2 mm in diameter can be levitated in a vacuum chamber between two electrodes positioned vertically with an electrostatic field in between. The field is controlled through a feed back system to keep the levitated sample at a predetermined position. Several copies of this system have been made in JAXA and NASA, and the original system has been transferred to Callifornia Institute of Technology with an upgraded setup of tetrahedra four beam laser heating system.On the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
the photoelectric effect
Photoelectric effect
In the photoelectric effect, electrons are emitted from matter as a consequence of their absorption of energy from electromagnetic radiation of very short wavelength, such as visible or ultraviolet light. Electrons emitted in this manner may be referred to as photoelectrons...
and electrons in the solar wind
Solar wind
The solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in temperature and speed over time...
charges fine layers of moon dust on the surface forming an atmosphere of dust floating in "fountains" over the surface of the moon.
See also
- Magnetic levitationMagnetic levitationMagnetic levitation, maglev, or magnetic suspension is a method by which an object is suspended with no support other than magnetic fields...
- Optical levitationOptical levitationOptical levitation is a method developed by Arthur Ashkin whereby a material is levitated against the downward force of gravity by an upward force stemming from photon momentum transfer...
- Acoustic levitationAcoustic levitationAcoustic levitation is a method for suspending matter in a medium by using acoustic radiation pressure from intense sound waves in the medium. Acoustic levitation is possible because of the non-linear effects of intense sound waves....
- Aerodynamic levitationAerodynamic levitationAerodynamic levitation is the use of gas pressure to levitate materials so that they are no longer in physical contact with any container. In scientific experiments this removes contamination and nucleation issues associated with physical contact with a container.-Overview:The term aerodynamic...
- Biefeld-Brown effect
- EHD thruster
- IonocraftIonocraftAn ionocraft or ion-propelled aircraft, commonly known as a lifter or hexalifter, is an electrohydrodynamic device to produce thrust in the air, without requiring any combustion or moving parts. The term "Ionocraft" dates back to the 1960s, an era in which EHD experiments were at their peak...
(Lifter)