运动是相对的.定压管中的流体快速流过管凸壁段的流动可视为管凸壁相对管中压力固定的静止流体的运动.圆柱物体在其周围自由固定压力不受影响的大气和水中的轴向运动,不仅可视为物体在定压管中的运动,而且还可视为管中的定压流体快速流过静止物体的流动,因为自由压力域在径向是管壁、在轴向是管中固定压力.实际上,任何在固定压力下流过物外表和管内壁的流体,都将被迎流面的轴向正阻力或正流抗把其部分压力能转为动能,被背流面的轴向负阻力或负流抗把其部分动能转回压力能,试图使其不耗能地快速流过所遇到的障碍;或者说,任何流体流动都遵守同一压力随流速而变的机制,有与管道完全相同的压力场和速度场;或者说,毫无疑问,流体压力随流速而变的各种常见应用和课堂演示本来应该有一个统一的科学解释.%Movements are relative. The rapid flowing of a fluid through a wall-bulged passage of pipes at a certain pressure can be regarded as a movement of the bulged wall relative to a static fluid in a certainly pressurized pipe. The axial movement of a cylindrical object in the atmosphere and the water whose free certain pressure is not influenced can be regarded not only as the object's movement in a certainly pressurized pipe but also as the rapid flowing of a fluid in a certainly pressurized pipe past a static object, because the free pressure region is a radial wall and an axial certain pressure of a pipe. Actually, any fluid that flows past an object or a pipe wall at a certain pressure will have a part of its pressure energy converted into its kinetic energy by an axial positive resistance or positive fluid reactance from their windward, and have a part of its kinetic energy converted back into its pressure energy by an axial negative resistance or negative fluid reactance from their leeward, attempting to cause it to flow rapidly past an obstacle met by it without consumption of energy;or any flow of fluids obeys the same mechanism of changes in pressure with velocity and has the same pressure and velocity fields as a flow in a pipe;or it is undoubted that all the common applications and demonstrations of changes in pressure with velocity should have had a uniform scientific explanation.
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