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The Mach number (M or Ma), often only Mach, (/ mɑːk /; German: [max]) is a dimensionless quantity in fluid dynamics representing the ratio of flow velocity past a boundary to the local speed of sound. [1][2] It is named after the Austrian physicist and philosopher Ernst Mach. where: M is the local Mach number, u is the local flow velocity ...
The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elastic medium. More simply, the speed of sound is how fast vibrations travel. At 20 °C (68 °F), the speed of sound in air is about 343 m/s (1,125 ft/s; 1,235 km/h; 767 mph; 667 kn), or 1 km in 2.91 s or one mile in 4.69 s.
Hypersonic flight is flight through the atmosphere below altitudes of about 90 km (56 mi) at speeds greater than Mach 5, a speed where dissociation of air begins to become significant and high heat loads exist. Speeds over Mach 25 have been achieved below the thermosphere as of 2020. [citation needed] Reentry vehicle (RV) after an 8,000 ...
For example, if the M MO is Mach 0.83, then at 9,100 m (30,000 ft) where the speed of sound under standard conditions is 1,093 kilometres per hour (590 kn), the true airspeed at M MO is 906 kilometres per hour (489 kn). The speed of sound increases with air temperature, so at Mach 0.83 at 3,000 m (10,000 ft) where the air is much warmer than at ...
Supersonic speed is the speed 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 (1,126 ft/s; 768 mph; 667.1 kn; 1,236 km/h). Speeds greater than five times the speed of sound (Mach 5) are often referred to as hypersonic.
Hypersonic speed. "Hypersonic" redirects here. For other uses, see Hypersonic (disambiguation). In aerodynamics, a hypersonic speed is one that exceeds five times the speed of sound, often stated as starting at speeds of Mach 5 and above. [1] The precise Mach number at which a craft can be said to be flying at hypersonic speed varies, since ...
Airspeed is commonly given in knots (kn). Since 2010, the International Civil Aviation Organization (ICAO) recommends using kilometers per hour (km/h) for airspeed (and meters per second for wind speed on runways), but allows using the de facto standard of knots, and has no set date on when to stop.
For example, the speed of sound at 30,000 feet (9,100 m) is about 670 miles per hour (1,080 km/h), but an aircraft must travel at least 750 miles per hour (1,210 km/h) (Mach 1.12) for a boom to be heard on the ground. [6] The composition of the atmosphere is also a factor.