✓ Sources checked · 10 September 2026 · View verification
Supersonic means faster than the local speed of sound relative to the surrounding medium: Mach number M = V/c is greater than one. It is not a single fixed speed in kilometres per hour.
By Matan · Updated
Temperature changes the threshold in air
For ideal air of fixed composition, sound speed varies approximately with the square root of absolute temperature. The same aircraft airspeed can therefore correspond to different Mach numbers in different conditions. Use air-relative speed, not groundspeed. [1]
Worked two-temperature comparison
An object moves at 400 m/s. If local sound speed is 343 m/s, M = 1.166. If sound speed is 295 m/s, M = 1.356. The speed is 1440 km/h in both cases, and both cases are supersonic, but their Mach numbers differ.
Small disturbances cannot run upstream
When flow is supersonic, small acoustic signals cannot propagate upstream against it. Compression can form shocks. In the ideal weak-disturbance geometry, Mach-cone half-angle satisfies sinμ = 1/M, giving μ = 30° at M = 2. A finite-strength shock angle generally differs from this Mach angle.
A flow can contain several regimes
Even around an aircraft with subsonic freestream, some local regions may become supersonic in transonic flow. Sonic-boom footprint and loudness depend on shape, trajectory and atmospheric propagation. Historical or proposed aircraft programs are not needed to define the underlying speed regime.
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How this article was checked
Sources checked; calculations checked where shown. Main claims and model assumptions were checked against the references below. Example arithmetic and units were checked separately. Numerical examples are illustrative calculations, not experimental measurements.
Source checking and editing assisted by AI. No independent human scientific review is recorded for this revision. This record applies to the version dated 10 September 2026.
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Cite this article
Matan. “Supersonic speed.” Your Physicist. Originally published 2023-03-20; updated 2026-09-10. https://your-physicist.com/supersonic-speed/
Revision history
10 September 2026: Removed stale aircraft-development claims and fixed-speed language and added local-Mach comparisons. Added references and a transparent verification record.
