Sonic boom faster than the speed of sound, thus creating a sonic boom. The whip is probably the first human invention to break the sound barrier. A bullwhip tapers down from the handle section to the cracker. The cracker has much less mass than the handle section. When the whip is sharply swung, the energy is transferred down the length of the tapering whip. Goriely and McMillen showed that the physical explanation is complex, involving the way that a loop travels down a tapered filament under tension. Sonic boom A sonic boom is the sound associated with the shock waves created whenever
Periodic travelling wave wave speeds. For partial differential equations, periodic travelling waves typically occur for a continuous range of wave speeds. An important question is whether a periodic travelling wave is stable or unstable as a solution of the original mathematical system. For partial differential equations, it is typical that the wave family subdivides into stable and unstable parts. For unstable periodic travelling waves, an important subsidiary question is whether they are absolutely or convectively unstable, meaning that there are or are not stationary growing linear modes. This issue has only been resolved for a few partial differential equations. A number of mechanisms