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人们在生活中经常会遇到这样的现象:看到飞机在空中掠过片刻后,才听见空中飞机震耳的隆隆声。这是为什么呢?原来这是飞机的飞行速度v大于声音在空气中的传播速度v_0,发生典型的多普勒效应。著名的奥地利物理学家E.马赫在研究一个微弱的点扰源(如尖头弹丸)运动时,发现当弹丸以超声速在空气中运动时,存在一个以点扰源为顶点的锥面,人必须站在锥面之内,才能听到弹丸的声音,人站在圆锥之外,无论离点扰源多近,都不会听到声音,这个圆锥就称为“马赫锥”(Mach cone),这现象常称为“马赫效应”。
People in life often encounter such a phenomenon: saw the aircraft passing in the air after a while, only to hear the rumble of airborne aircraft. Why is this? It turned out that this is the aircraft flight speed v is greater than the sound velocity in air v_0, a typical Doppler effect. When studying the movement of a weak point source such as a pointed projectile, the famous Austrian physicist E. Mach discovered that when the projectile moves in air at supersonic speeds, there is a cone whose vertex is a point source Must stand within the cone, in order to hear the sound of the projectile, the person standing outside the cone, no matter how close the disturbance from point to point, the sound will not be heard, the cone is called “Mach cone” (Mach cone), this phenomenon is often called “Mach effect ”.