Convert from mile/hour to mach

Unit Definition (mile/hour)
The mile per hour is a unit of speed, expressing the number of international miles covered per hour. It is currently the unit used for speed limits, and speeds, on roads in the United Kingdom, United States and other nations. It is also used to express the speed of delivery of a ball in various sporting events, such as cricket, tennis, and baseball at the higher levels of competition. A common abbreviation is mph or MPH, although mi/h is sometimes used in technical publications. In the International System of Units (SI), the unit of speed or velocity is m/s. Road traffic speeds, in most countries, are quoted in km/h. Nautical and aeronautical applications, however, favor the knot as a common unit of speed: one knot is one nautical mile per hour.

Unit Definition (mach)
The Mach is a measure of velocity relative to the speed of sound. The precise speed of sound varies with the density and temperature of the atmosphere, although at 0 °C (at 1atm.) the speed of sound is 331.6 m/s. The mach speed is important to the control of an aircraft, especially at speeds close to or exceeding Mach 1.0. The unit is named after the Austrian physicist Ernst Mach.