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例题一般情况下,不转动的乒乓球飞行的弧线如图1中E线所示.为了使乒乓球的飞行弧线比E线高些,则飞行的乒乓球应该怎样旋转? 解析要解答这个问题,应先分析乒乓球上、下气流的速度,再根据伯努利方程确定乒乓球上、下压力的大小关系. 如果乒乓球在飞行过程中不旋转,则上下、左右气流的速度相等.如果乒乓球相对于水平轴产生向下旋转,如图2所示,乒乓球上、下气流的速度就不相等了.由于乒
Example In general, the arc of a non-rotating ping pong ball is shown as line E in Figure 1. In order to make the flying arc of the ping pong ball higher than the E line, how should the flying ping pong ball be rotated? In order to solve this problem, we must first analyze the speed of the air flow above and below the ping-pong ball. Then, according to the Bernoulli equation, determine the relationship between the pressure of the ping-pong ball. If the ping-pong balls do not rotate during the flight, the speeds of the upper and lower air flows are equal. If the table tennis ball is rotated downward with respect to the horizontal axis, as shown in Fig. 2, the speeds of the upper and lower air flows of the table tennis ball are not equal.