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Levitate
Levitation (from Latin ''levitas'' "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 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diamagnetic Levitation
Magnetic levitation (maglev) or magnetic suspension is a method by which an object is levitation, suspended with no support other than magnetic fields. Lorentz force, Magnetic force is used to counteract the effects of the gravitational force and any other forces. The two primary issues involved in magnetic levitation are ''lifting forces'': providing an upward force sufficient to counteract gravity, and ''stability'': ensuring that the system does not spontaneously slide or flip into a configuration where the lift is neutralized. Magnetic levitation is used for maglev trains, Induction heating, contactless melting, magnetic bearings and for product display purposes. Lift Magnetic materials and systems are able to attract or repel each other with a force dependent on the magnetic field and the area of the magnets. For example, the simplest example of lift would be a simple dipole magnet positioned in the magnetic fields of another dipole magnet, oriented with like poles faci ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Maglev
Maglev (derived from '' magnetic levitation''), is a system of train transportation that uses two sets of electromagnets: one set to repel and push the train up off the track, and another set to move the elevated train ahead, taking advantage of the lack of friction. Such trains rise approximately off the track. There are both high speed, intercity maglev systems (over ), and low speed, urban maglev systems ( to ) being built and under construction and development. With maglev technology, the train travels along a guideway of electromagnets which control the train's stability and speed. While the propulsion and levitation require no moving parts, the bogies can move in relation to the main body of the vehicle and some technologies require support by retractable wheels at low speeds under . This compares with electric multiple units that may have several dozen parts per bogie. Maglev trains can therefore in some cases be quieter and smoother than conventional trains and have t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Buoyant Levitation
Levitation (from Latin ''levitas'' "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 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diamagnetic
Diamagnetic materials are repelled by a magnetic field; an applied magnetic field creates an induced magnetic field in them in the opposite direction, causing a repulsive force. In contrast, paramagnetic and ferromagnetic materials are attracted by a magnetic field. Diamagnetism is a quantum mechanical effect that occurs in all materials; when it is the only contribution to the magnetism, the material is called diamagnetic. In paramagnetic and ferromagnetic substances, the weak diamagnetic force is overcome by the attractive force of magnetic dipoles in the material. The magnetic permeability of diamagnetic materials is less than the permeability of vacuum, ''μ''0. In most materials, diamagnetism is a weak effect which can be detected only by sensitive laboratory instruments, but a superconductor acts as a strong diamagnet because it repels a magnetic field entirely from its interior. Diamagnetism was first discovered when Anton Brugmans observed in 1778 that bismuth was repel ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrodynamic Suspension
Electrodynamic suspension (EDS) is a form of magnetic levitation in which there are conductors which are exposed to time-varying magnetic fields. This induces eddy currents in the conductors that creates a repulsive magnetic field which holds the two objects apart. These time varying magnetic fields can be caused by relative motion between two objects. In many cases, one magnetic field is a permanent field, such as a permanent magnet or a superconducting magnet, and the other magnetic field is induced from the changes of the field that occur as the magnet moves relative to a conductor in the other object. Electrodynamic suspension can also occur when an electromagnet driven by an AC electrical source produces the changing magnetic field, in some cases, a linear induction motor generates the field. EDS is used for maglev trains, such as the Japanese SCMaglev. It is also used for some classes of magnetically levitated bearings. Types Many examples of this have been used over the y ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Magnet 4
A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nickel, cobalt, etc. and attracts or repels other magnets. A permanent magnet is an object made from a material that is magnetized and creates its own persistent magnetic field. An everyday example is a refrigerator magnet used to hold notes on a refrigerator door. Materials that can be magnetized, which are also the ones that are strongly attracted to a magnet, are called ferromagnetic (or ferrimagnetic). These include the elements iron, nickel and cobalt and their alloys, some alloys of rare-earth metals, and some naturally occurring minerals such as lodestone. Although ferromagnetic (and ferrimagnetic) materials are the only ones attracted to a magnet strongly enough to be commonly considered magnetic, all other substances respond weakly to a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Screening Current
The Meissner effect (or Meissner–Ochsenfeld effect) is the expulsion of a magnetic field from a superconductor during its transition to the superconducting state when it is cooled below the critical temperature. This expulsion will repel a nearby magnet. The German physicists Walther Meissner and Robert Ochsenfeld discovered this phenomenon in 1933 by measuring the magnetic field distribution outside superconducting tin and lead samples. The samples, in the presence of an applied magnetic field, were cooled below their superconducting transition temperature, whereupon the samples cancelled nearly all interior magnetic fields. They detected this effect only indirectly because the magnetic flux is conserved by a superconductor: when the interior field decreases, the exterior field increases. The experiment demonstrated for the first time that superconductors were more than just perfect conductors and provided a uniquely defining property of the superconductor state. The ability ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radiation Pressure
Radiation pressure is the mechanical pressure exerted upon any surface due to the exchange of momentum between the object and the electromagnetic field. This includes the momentum of light or electromagnetic radiation of any wavelength that is absorbed, reflected, or otherwise emitted (e.g. black-body radiation) by matter on any scale (from macroscopic objects to dust particles to gas molecules). The associated force is called the radiation pressure force, or sometimes just the force of light. The forces generated by radiation pressure are generally too small to be noticed under everyday circumstances; however, they are important in some physical processes and technologies. This particularly includes objects in outer space, where it is usually the main force acting on objects besides gravity, and where the net effect of a tiny force may have a large cumulative effect over long periods of time. For example, had the effects of the Sun's radiation pressure on the spacecraft of the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Momentum
In Newtonian mechanics, momentum (more specifically linear momentum or translational momentum) is the product of the mass and velocity of an object. It is a vector quantity, possessing a magnitude and a direction. If is an object's mass and is its velocity (also a vector quantity), then the object's momentum is : \mathbf = m \mathbf. In the International System of Units (SI), the unit of measurement of momentum is the kilogram metre per second (kg⋅m/s), which is equivalent to the newton-second. Newton's second law of motion states that the rate of change of a body's momentum is equal to the net force acting on it. Momentum depends on the frame of reference, but in any inertial frame it is a ''conserved'' quantity, meaning that if a closed system is not affected by external forces, its total linear momentum does not change. Momentum is also conserved in special relativity (with a modified formula) and, in a modified form, in electrodynamics, quantum mechanics, quan ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Photon
A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they always move at the speed of light in vacuum, (or about ). The photon belongs to the class of bosons. As with other elementary particles, photons are best explained by quantum mechanics and exhibit wave–particle duality, their behavior featuring properties of both waves and particles. The modern photon concept originated during the first two decades of the 20th century with the work of Albert Einstein, who built upon the research of Max Planck. While trying to explain how matter and electromagnetic radiation could be in thermal equilibrium with one another, Planck proposed that the energy stored within a material object should be regarded as composed of an integer number of discrete, equal-sized parts. To explain the photoelectric effect, Eins ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hovercraft
A hovercraft, also known as an air-cushion vehicle or ACV, is an amphibious Craft (vehicle), craft capable of travelling over land, water, mud, ice, and other surfaces. Hovercraft use blowers to produce a large volume of air below the hull, or air cushion, that is slightly above atmospheric pressure. The pressure difference between the higher pressure air below the hull and lower pressure ambient air above it produces lift, which causes the hull to float above the running surface. For stability reasons, the air is typically blown through slots or holes around the outside of a disk- or oval-shaped platform, giving most hovercraft a characteristic rounded-rectangle shape. The first practical design for hovercraft was derived from a British invention in the 1950s. They are now used throughout the world as specialised transports in disaster relief, coastguard, military and survey applications, as well as for sport or passenger service. Very large versions have been used to t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ping Pong Ball
Table tennis, also known as ping-pong and whiff-whaff, is a sport in which two or four players hit a lightweight ball, also known as the ping-pong ball, back and forth across a table using small solid rackets. It takes place on a hard table divided by a net. Except for the initial serve, the rules are generally as follows: Players must allow a ball played toward them to bounce once on their side of the table and must return it so that it bounces on the opposite side. A point is scored when a player fails to return the ball within the rules. Play is fast and demands quick reactions. Spinning the ball alters its trajectory and limits an opponent's options, giving the hitter a great advantage. Table tennis is governed by the worldwide organization International Table Tennis Federation (ITTF), founded in 1926. ITTF currently includes 226 member associations. The official rules are specified in the ITTF handbook. Table tennis has been an Olympic sport since 1988, with several event c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
