The prefix Mach is used to describe an airplane's true airspeed relative to the local speed of sound. It derives form Ernst Mach, an Austrian scientist who contributed to the study of sound. When a plane moves at the speed of sound (in air) it is Mach 1. When twice the speed of sound it is Mach 2. At Mach 0.5, an airplane is travelling at half the local speed of sound. When a plane flies faster than sound travels, listeners hear a sonic boom.
The speed of sound in air is 770 mph, or 1130 ft/s (1230 km/h or 344 m/s) in dry air at 70F. Sound travels faster in water than it does in air, and even faster in iron and steel.
- Wile, Dr. Jay L. Exploring Creation With Physical Science. Apologia Educational Ministries, Inc. 1999, 2000
- Speed of Sound http://hyperphysics.phy-astr.gsu.edu/hbase/sound/souspe.html, Retrieved 7March2008