Photo: vissago (flickr)
Last time on A Moment of Science we looked at how sonic booms are created by planes flying at supersonic speeds. This time we’ll look at how the size and altitude of a plane influence the intensity and duration of the sonic boom.
The sonic boom is a direct result of a change in the air-flow pattern around a plane’s edges. The moment a plane hits speeds faster than about 768 miles per hour, or the speed of sound, it creates shock waves that travel in all directions. When these shock waves hit the ground, we hear a sonic boom.
As a general rule, the bigger the aircraft, the larger the shock waves and the longer the duration of the sonic boom. The smallest aircraft capable of traveling faster than the speed of sound generates a boom that lasts one twentieth of a second. The largest supersonic aircraft creates a boom that lasts ten times longer, or half a second.
However, two aircraft the same size flying at different altitudes will create sonic booms of different intensities. A craft flying higher will create a less intense sonic boom at ground level, because the shock waves have farther to travel before hitting the ground, and therefore have more time to dissipate.
The sonic boom created by this high flying plane will be heard by a larger geographic area than the boom created by a low flying plane because as the shock waves travel to the ground, they spread out and increase the radius they affect.
Luckily, even the most intense sonic booms can’t hurt people, but they have been known to damage plaster walls and break windows.