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A lifting bag is an item of diving equipment consisting of a robust and air-tight bag with straps, which is used to lift heavy objects underwater by means of the bag's buoyancy. The heavy object can either be moved horizontally underwater by the diver or sent unaccompanied to the surface. Besides as a piece of diving equipment there are also lifting bags used on land for lifting cars or heavy loads or lifting bags which are used in machines. These lifting bags of the AS/CR type are for example used in the brake mechanism of (rollercoasters ). It is advisable to select a lift bag with an appropriate capacity for the task at hand. If the lift bag is grossly oversized a runaway or otherwise out of control ascent may result. Commercially available lifting bags may also incorporate dump valves to allow the operator to control the bags buoyancy during ascent. If a single bag is insufficient, multiple bags may be used, and should be distributed to suit the load. ==Physics of buoyant lifting== The volume of the bag determines its lifting capacity: a bag can lift a underwater object. A partially filled bag will accelerate as it ascends because the air in the bag expands as the pressure reduces on the ascent, following Boyles law, increasing the bag's buoyancy, whereas a full bag will overflow or blow off excess volume and maintain the same volume and buoyancy providing is does not descend. A bag which leaks sufficiently to start sinking will lose volume to compression and become less buoyant in a positive feedback loop until stopped by the bottom. 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「lifting bag」の詳細全文を読む スポンサード リンク
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