layers due to cooling. The cooling tends toincrease the density of the air.Atmospheric pressures are quite large, but inmost instances practically the same pressure ispresent on all sides of objects so that no singlesurface is subjected to a great load.Atmospheric pressure acting on the surface ofa liquid (fig. 2-3, view A) is transmitted equallythroughout the liquid to the walls of the container,but is balanced by the same atmospheric pressureacting on the outer walls of the container. In viewB of figure 2-3, atmospheric pressure acting onthe surface of one piston is balanced by the samepressure acting on the surface of the other piston.The different areas of the two surfaces make nodifference, since for a unit of area, pressures arebalanced.TRANSMISSION OF FORCESTHROUGH LIQUIDSWhen the end of a solid bar is struck, the mainforce of the blow is carried straight through thebar to the other end (fig. 2-4, view A). Thishappens because the bar is rigid. The directionof the blow almost entirely determines thedirection of the transmitted force. The more rigidFigure 2-4.—Transmission of force: (A) solid; (B) fluid.the bar, the less force is lost inside the bar ortransmitted outward at right angles to thedirection of the blow.When a force is applied to the end of a columnof confined liquid (fig. 2-4, view B), it istransmitted straight through to the other end andalso equally and undiminished in every directionthroughout the column—forward, backward, andsideways—so that the containing vessel is literallyfilled with pressure.An example of this distribution of force isillustrated in figure 2-5. The flat hose takes onFigure 2-3.—Effects of atmospheric pressure.Figure 2-5.—Distribution of force.2-3
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