時間：2011-03-11 23:11來源：藍天飛行翻譯 作者：admin 點擊：次
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arc cosine. The trigonometric function that means “the angle whose cosine is.” For example, arc cos 0.866 = 30°, means that the angle whose cosine is 0.866 is 30°. Arc cosine is usually written cos-1. See cosine. arch (structure). A form of structure with curving sides and a wedge-shaped keystone at the top. An arch supports weight by transmitting the force caused by its weight through its curving sides into the structure supporting it. The forces supported by the arch are transmitted into the sides through the keystone. Archimedes’ principle. The principle of buoyancy, propounded by the Greek mathematician Archimedes. Archimedes’ principle states that an object immersed in a fluid loses as much of its own weight as the weight of the fluid it displaces. The sciences of hydrostatics and aerostatics are based on Archimedes’ principle. arcing. Sparking between a commutator and brush or between switch contacts when the flow of current is interrupted. Arcing occurs when induction tries to keep the current flowing across the broken contact. arc lamp. A source of light produced by an electric arc which is an intense and continuous spark. The arc is produced when electrons flow through ionized gases between two electrodes. arc sine. The trigonometric function that means “the angle whose sine is.” For example, arc sin 0.707 = 45°, means that the angle whose sine is 0.707 is 45°. Arc sine is usually written sin-1. See sine. arc tangent. A value used in trigonometry that is the inverse, or opposite, of the tangent. This is the same as one divided by the tangent. The tangent of an angle is the ratio of the length of the side opposite the angle, to the length of the side adjacent, or next to, the angle. If the sides of a triangle that form a right angle are two inches and three inches, the tangent of one of the angles is 2/3, or 0.667. The arc tangent is the angle whose tangent is 0.667, and this is 33.7°. This is normally written as Tan-1 0.667. See tangent. arc welding. A form of electric welding in which the intense heat needed to melt the metal is produced by an electric arc. arctic air. The air in a mass formed over an arctic area of ice and snow. The air has the characteristics of this type of area. arctic front (meteorology). The surface discontinuity between very cold (arctic) air flowing directly from the arctic region and another less cold and, consequently, less dense air mass. area. A measurement of the amount of surface of an object. Area is usually expressed in such units as square inches or square centimeters for small surfaces or in square feet or square meters for larger surfaces. area control center (ICAO). An ICAO term for an air traffic control facility primarily responsible for ATC services being provided IFR aircraft during the en route phase of flight. The U.S. equivalent is an air route traffic control center (ARTCC). |
