- published: 17 Jun 2010
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Supersonic speed is a rate of travel of an object that exceeds the speed of sound (Mach 1). For objects traveling in dry air of a temperature of 20 °C (68 °F) at sea level, this speed is approximately 343.2 m/s, 1,125 ft/s, 768 mph, 667 knots, or 1,235 km/h. Speeds greater than five times the speed of sound (Mach 5) are often referred to as hypersonic. Flights during which only some parts of the air surrounding an object, such as the ends of rotor blades, reach supersonic speeds are called transonic. This occurs typically somewhere between Mach 0.8 and Mach 1.23.
Sounds are traveling vibrations in the form of pressure waves in an elastic medium. In gases, sound travels longitudinally at different speeds, mostly depending on the molecular mass and temperature of the gas, and pressure has little effect. Since air temperature and composition varies significantly with altitude, Mach numbers for aircraft may change despite a constant travel speed. In water at room temperature supersonic speed can be considered as any speed greater than 1,440 m/s (4,724 ft/s). In solids, sound waves can be polarized longitudinally or transversely and have even higher velocities.
The sound barrier or sonic barrier is a popular term for the sudden increase in aerodynamic drag and other effects experienced by an aircraft or other object when it approaches supersonic speed. When aircraft first began to be able to reach close to supersonic speed, these effects were seen as constituting a barrier making supersonic speed very difficult or impossible.
In dry air at 20 °C (68 °F), the sound barrier is reached when an object moves at a speed of 343 metres per second (about 767 mph, 1234 km/h or 1,125 ft/s). The term came into use in this sense during World War II, when a number of aircraft started to encounter the effects of compressibility, a number of unrelated aerodynamic effects that "struck" their aircraft, seemingly impeding further acceleration. By the 1950s, new aircraft designs routinely "broke" the sound barrier.
Some common whips such as the bullwhip or sparewhip are able to move faster than sound: the tip of the whip breaks the sound barrier and causes a sharp crack—literally a sonic boom.Firearms since the 19th century have generally had a supersonic muzzle velocity.