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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 ...
Speed of sound. 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.
World Cup. 2006 Athens. 200 m. Usain St. Leo Bolt OJ CD (/ ˈjuːseɪn /; [ 12 ] born 21 August 1986) is a Jamaican retired sprinter who is widely considered to be the greatest sprinter of all time. [ 13 ][ 14 ][ 15 ] He is an eight-time Olympic gold medalist and the world record holder in the 100 metres, 200 metres, and 4 × 100 metres relay.
Usain Bolt (center right) wins his first world title in world record time. The men's 100 metres at the 2009 World Championships in Athletics were held at the Olympic Stadium on August 15 and August 16. The two main contenders for the event were the reigning World Champion Tyson Gay and Usain Bolt, the reigning Olympic champion and world record ...
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.
The subsonic speed range is that range of speeds within which, all of the airflow over an aircraft is less than Mach 1. The critical Mach number (Mcrit) is lowest free stream Mach number at which airflow over any part of the aircraft first reaches Mach 1. So the subsonic speed range includes all speeds that are less than Mcrit.
Therefore, for a boom to reach the ground, the aircraft's speed relative to the ground must be greater than the speed of sound at the ground. 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 ...
Bolt set a new Olympic record (beating his own record set at the 2008 Olympic Games) of 9.64 seconds, later rounded down to 9.63 seconds. Blake edged past Gatlin, who in turn held off a closing Gay at the finish line. [11] [12] Usain Bolt was the second athlete after Carl Lewis (1984, 1988) to retain the men's 100m championship. His winning ...