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g-force (with ''g'' from ''gravitational'') is a measurement of the type of acceleration that causes weight. Despite the name, it is incorrect to consider g-force a fundamental force, as "g-force" (lower case character) is a type of acceleration that can be measured with an accelerometer. Since g-force accelerations indirectly produce weight, any g-force can be described as a "weight per unit mass" (see the synonym specific weight). When the g-force acceleration is produced by the surface of one object being pushed by the surface of another object, the reaction-force to this push produces an equal and opposite weight for every unit of an object's mass. The types of forces involved are transmitted through objects by interior mechanical stresses. The g-force acceleration (save for certain electromagnetic force influences) is the cause of an object's acceleration in relation to free-fall.〔(G Force ). Newton.dep.anl.gov. Retrieved on 2011-10-14.〕 The g-force acceleration experienced by an object is due to the vector sum of all non-gravitational and non-electromagnetic forces acting on an object's freedom to move. In practice, as noted, these are surface-contact forces between objects. Such forces cause stresses and strains on objects, since they must be transmitted from an object surface. Because of these strains, large g-forces may be destructive. Gravitation acting alone does not produce a g-force, even though g-forces are expressed in multiples of the acceleration of a standard gravity. Thus, the standard gravitational acceleration at the Earth's surface produces g-force only indirectly, as a result of resistance to it by mechanical forces. These mechanical forces actually produce the g-force acceleration on a mass. For example, the 1 g force on an object sitting on the Earth's surface is caused by mechanical force exerted in the upward direction by the ground, keeping the object from going into free-fall. The upward contact-force from the ground ensures that an object at rest on the Earth's surface is accelerating relative to the free-fall condition (Free fall is the path that the object would follow when falling freely toward the Earth's center). Stress inside the object is ensured from the fact that the ground contact forces are transmitted only from the point of contact with the ground. Objects allowed to free-fall in an ''inertial trajectory'' under the influence of gravitation-only, feel no g-force acceleration, a condition known as zero-g (which means zero g-force). This is demonstrated by the "zero-g" conditions inside a freely falling elevator falling toward the Earth's center (in vacuum), or (to good approximation) conditions inside a spacecraft in Earth orbit. These are examples of coordinate acceleration (a change in velocity) without a sensation of weight. The experience of no g-force (zero-g), however it is produced, is synonymous with weightlessness. In the absence of gravitational fields, or in directions at right angles to them, proper and coordinate accelerations are the same, and any coordinate acceleration must be produced by a corresponding g-force acceleration. An example here is a rocket in free space, in which simple changes in velocity are produced by the engines, and produce g-forces on the rocket and passengers. ==Unit and measurement== The unit of measure of acceleration in the International System of Units (SI) is m/s2. However, to distinguish acceleration relative to free-fall from simple acceleration (rate of change of velocity), the unit g (or ''g'') is often used. One ''g'' is the acceleration due to gravity at the Earth's surface and is the standard gravity (symbol: ''g''n), defined as metres per second squared,〔BIPM: (Declaration on the unit of mass and on the definition of weight; conventional value of gn )〕 or equivalently newtons of force per kilogram of mass. Note that the ''unit definition'' does not vary with location — the g-force when standing on the moon is about 0.181 g. The unit g is not one of the SI units, which uses "g" for gram. Also "g" should not be confused with "G", which is the standard symbol for the gravitational constant.〔Symbol g: ESA: GOCE, ''(Basic Measurement Units )'', NASA: ''(Multiple G )'', Astronautix: ''(Stapp )'', Honeywell: ''(Accelerometers )'', Sensr LLC: ''(GP1 Programmable Accelerometer )'', Farnell: ''(accelometers )'', Delphi: ''(Accident Data Recorder 3 (ADR3) MS0148 )'', NASA: ''(Constants and Equations for Calculations )'', Jet Propulsion Laboratory: ''(A Discussion of Various Measures of Altitude )'', Vehicle Safety Research Centre Loughborough: ''(Use of smart technologies to collect and retain crash information )'', National Highway Traffic Safety Administration: ''(Recording Automotive Crash Event Data )'' Symbol G: Lyndon B. Johnson Space Center: ''(ENVIRONMENTAL FACTORS: BIOMEDICAL RESULTS OF APOLLO, Section II, Chapter 5 )'', Honywell: ''(Model JTF, General Purpose Accelerometer )''〕 This notation is commonly used in aviation, especially in acrobatic or combat military aviation, to describe the increased forces that must be overcome by pilots in order to remain conscious and not G-LOC (G-induced loss of consciousness).〔(【引用サイトリンク】url=http://goflightmedicine.com/pulling-gs/ )〕 For example, it is often said an F-16 fighter jet is able to sustain up to 9 G's for a limited time. Measurement of g-force is typically achieved using an accelerometer (see discussion below in Measuring g-force using an accelerometer). In certain cases, g-forces may be measured using suitably calibrated scales. Specific force is another name that has been used for g-force. 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「G-force」の詳細全文を読む スポンサード リンク
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