Supersonic speed motion faster than the speed of sound in a brittle material. At the beginning of the 20th century, the term "supersonic" was used as an adjective to describe sound whose frequency is above the range of normal human hearing. The modern term for this meaning is "ultrasonic". The tip of a bullwhip is thought to be the first man-made object to break the sound barrier, resulting in the telltale "crack" (actually a small sonic boom). The wave motion traveling through the bullwhip is what makes it capable of achieving supersonic speeds. Most modern fighter aircraft are supersonic aircraft, but there
Undercompressive shock wave a sharp wave front which remains so when it travels. A shock wave is undercompressive if these conditions are not fulfilled. A solution exists where a sharp wave front may remain sharp whilst travelling even when perturbations behind the front travel slower than it. An experiment can be made to show this with travelling liquid steps : a thick film is spread on a thin one. The liquid steps remain sharp when they travel because the spreading is enhanced by the Marangoni effect. Making little perturbations with the tip of a hair, one can see whether shock waves are compressive