Sunday, December 11, 2005

Weird Science: Sonic Boom(s)

Busy times are happening for me and my family around Christmas, so today will be a short look at the sonic boom. In fact there isn’t one sonic boom but two main ones and lots of minor ones.

But what is a sonic boom? Well, as objects travel below the speed of sound (Mach 1) the air in front of the object is disturbed quite a distance in front of the solid object and not compressed too much. But, as the object passes the speed of sound the pressure rises very sharply at the intersection point between the air and the craft.

What occurs is the air is extremely compressed by the object pushing through it above the speed of sound, and the pressure rises very quickly in a localized space. This speeding object actually forces the molecules of air to collectively impact on each other at high pressure. And hence, a sonic boom as these millions of molecules collide.

But the interesting thing is there is not one sonic boom, but two main ones and lots of minor ones. One of the main sonic booms occurs at the front of the object and one occurs at the rear of the object. The many smaller sonic booms created by an aircraft flying above Mach 1 are created by the shapes and protrusions of the craft, but they usually combine and sound like one boom.

And you will only hear two if the main shock waves from the front and rear are around or above one tenth of a second apart. The faster the object travels, the more likely you will hear two booms as the velocity of the booms differs from front to rear.

Sorry for the short explanation, but time is pressing and I gotta move - but I’ll try to keep it under the speed of sound. Don’t want to disturb the neighbors or break any windows.

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