|
Levitation (from Latin ''levitas'' "lightness")〔''Levitate'', "to rise by virtue of lightness," from Latin ''levitas'' "lightness," patterned in English on ''gravitate'': (Online Etymology Dictionary )〕 is the process by which an object is held aloft, without mechanical support, in a stable position. 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Levitation」の詳細全文を読む スポンサード リンク
|