## Speed of Sound

The speed of sound is 761 mph, 1225 km/h, 340 m/s, or 661 knots at standard temperature, which is 15 degrees Celsius. Unlike the speed of light, which remains relatively constant almost, wherever it goes, the speed of sound changed depending on the density and temperature of what it is traveling through. If the temperature is colder the speed of sound travels faster and if temperature is hotter then the speed of sound travels slower. This is because the speed of sound will travel fasted in stiffer atmospheres and slower in denser atmospheres. The speed of sound is a vibration and the more it has to vibrate off of the more it will be able to resonate and keep moving. For example: the speed of sound will travel faster under water then in air because the vibration it gives off has more to repel itself off of.

The speed of sound also affects the aircraft forces. If the aircraft is moving slower then the speed of sound then it is said that the aircraft is subsonic. If the aircraft is moving close to or a little more then the speed of sound then the aircraft is trans sonic. If the aircraft is moving faster then the speed of sound then the aircraft is supersonic. The speed of the aircraft in relation to the speed of sound is called the Mach number. The Mach number is expressed as a percentage of the speed of sound. For example: if an aircraft was moving at 600 knots then the aircraft mach number would be 0.9 the speed of sound. Depending on the shape and size of the aircraft and the atmospheric conditions present shockwaves can form from the aircraft moving close to of faster then the speed of sound. A shock wave is the compression of the air from the speed of the aircraft through the air. These can be either negative or positive for the aircraft, but more often then not they are negative.

The speed of sound is mathematically defined as the letter ācā. As an equation it is generally represented by:

where: c = the speed of sound, C = coefficient of stiffness, g = density

Otherwise, when dealing with the speed of sound traveling through a gas the following equation is more commonly used:

where: c = the speed of sound, y = adiabatic index, P = pressure, g = density

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