Definition

1. Noun:
   • The ratio of the speed of a moving object (especially an aircraft) to the speed of sound in the surrounding medium: A dimensionless quantity used in aerodynamics to describe high-speed flight. A Mach number of 1 indicates the speed of sound (Mach 1), less than 1 is subsonic, and greater than 1 is supersonic.

Usage Examples

• Noun:
  • The jet accelerated, its mach number increasing from 0.8 to 1.2 as it broke the sound barrier.
  • Engineers must consider the effects of compressibility when an aircraft's mach number exceeds 0.3.
  • The scramjet is designed to operate efficiently at a hypersonic mach number above 5.

Advanced Usage

• "Critical mach number": The speed, expressed as a Mach number, at which airflow over some part of the aircraft first reaches the speed of sound.
  • As the aircraft approaches its critical mach number, control becomes more difficult.
• "Free-stream mach number": The Mach number of the undisturbed airflow far ahead of a moving object.
  • The wing's performance was tested at a free-stream mach number of 0.85.

Variants and Related Words

• Mach (adj): Often used as a shorthand in technical contexts (e.g., Mach speed, Mach tuck).
  • The pilot experienced Mach tuck as the aircraft went supersonic.
• Subsonic (adj): Of or relating to speeds less than Mach 1.
• Supersonic (adj): Of or relating to speeds greater than Mach 1.
• Hypersonic (adj): Of or relating to speeds much greater than Mach 5.

Synonyms

• Speed ratio (in the specific context of comparison to sound speed).

Related Phrases

• To break Mach 1: To exceed the speed of sound (Mach 1).
  • The test pilot's goal was to break Mach 1 in level flight.
• At Mach 2: Traveling at twice the speed of sound.
  • The reconnaissance plane can cruise at Mach 2.

Related Idioms

Noun

1. the ratio of the speed of a moving body to the speed of sound