mach number
C1/C2Technical/Scientific
Definition
Meaning
The ratio of the speed of an object moving through a fluid (especially air) to the speed of sound in that fluid.
A dimensionless quantity used in aerodynamics to characterize flow regimes (subsonic, transonic, supersonic, hypersonic) and is named after Austrian physicist Ernst Mach.
Linguistics
Semantic Notes
A 'Mach number' of 1 is the speed of sound. It is a unitless measurement. Often capitalized ('Mach') when used before the number.
Dialectal Variation
British vs American Usage
Differences
Spelling and pronunciation are identical. The word 'number' may be omitted slightly more often in American technical writing (e.g., 'flying at Mach 2').
Connotations
Identical strong technical/scientific connotations in both dialects.
Frequency
Extremely low frequency in general language; exclusive to physics, engineering, aviation, and space contexts.
Vocabulary
Collocations
Grammar
Valency Patterns
The aircraft has a Mach number of XThe flow reached a Mach number of XIt is traveling at Mach XVocabulary
Synonyms
Strong
Neutral
Weak
Vocabulary
Antonyms
Phrases
Idioms & Phrases
- “Break the sound barrier (related to reaching Mach 1)”
- “Go supersonic”
Usage
Context Usage
Business
Virtually never used.
Academic
Core term in aerodynamics, fluid mechanics, aerospace engineering, and physics papers.
Everyday
Only in discussions about jets, fighter planes, or space vehicles.
Technical
The primary context. Used to design aircraft, analyze flight data, and describe atmospheric re-entry.
Examples
By Part of Speech
verb
British English
- The prototype is designed to mach. (Extremely rare, technical shorthand)
American English
- The jet can mach. (Extremely rare, technical shorthand)
adjective
British English
- The Mach-number reading was unstable during transonic flight.
American English
- The Mach number indicator is a crucial cockpit instrument.
Examples
By CEFR Level
- The jet flew faster than the speed of sound.
- Concorde could travel at a speed greater than Mach 2.
- Engineers must account for compressibility effects once the Mach number exceeds 0.3.
Learning
Memory Aids
Mnemonic
Think 'Mach' sounds like 'mock'. Imagine mocking a slow plane by saying it can't even reach 'Mach 1' (the speed of sound).
Conceptual Metaphor
SPEED IS A NUMBER ON A SCALE (where 1 is a critical threshold - the sound barrier).
Watch out
Common Pitfalls
Translation Traps (for Russian speakers)
- Avoid translating as 'номер Маха' (incorrect). The correct Russian term is 'число Маха'.
Common Mistakes
- Pronouncing 'Mach' as /mætʃ/ (like 'match') instead of /mɑːk/ or /mɑːx/.
- Writing 'march number'.
- Using 'Mach' as a standalone unit with a plural 's' (e.g., 'Machs').
Practice
Quiz
What does a Mach number of 1 signify?
FAQ
Frequently Asked Questions
No. Airspeed is a direct speed measurement (e.g., km/h). Mach number is a ratio of that speed to the local speed of sound, which varies with air temperature and density.
It is named after Ernst Mach, a 19th-century Austrian physicist who studied the dynamics of projectiles moving faster than sound.
Yes. A Mach number less than 1 indicates subsonic flow (slower than sound). Between 0.8 and 1.2 is often called transonic.
Both are common. 'Mach one' is often used for the specific value of 1, while 'Mach 2', 'Mach 3', etc., are standard.