1. a number representing the ratio of the speed of an object to the speed of sound in the same medium
Usage: often used in aviation and aeronautics; named after physicist Ernst Mach

Examples

• The fighter jet traveled at Mach 2, twice the speed of sound.
• Commercial airplanes typically cruise at around Mach 0.85.
• At Mach 1, an aircraft reaches the sound barrier.
• The spacecraft accelerated to Mach 5 during its test flight.
• Pilots must understand Mach numbers to safely operate supersonic aircraft.