12.7 Sonic Boom

This can happen in air as an airplane travels faster than sound. Then this shock wave follows along behind the airplane and eventually touches the ground as shown in Figure 12.21. As this shock wave-this wave front of increased pressure-goes along the ground, it will be heard as a loud noise or felt as a burst of increased pressure. We call this a "sonic boom" and it may rattle or even break windows of buildings as it passes by. That is why supersonic flights are kept away from inhabited areas.

Figure 12.F The Concorde-flown by Air France and British Airways-is the only supersonic commercial aircraft in use today. Over inhabited areas, it flies subsonically (below the speed of sound). The Concorde is used primarily on long over-water routes where problems due to its sonic boom are minimal.

This shock wave of wave fronts piling up on one another also occurs when a boat travels through water faster than the speed of the waves across the surface of the water. Then a distinctive "bow wave" is produces as shown in Figure 12.22.

Figure 12.22 As a boat travels faster than the surface wave speed, a bow wave is created.

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