Why the Speed of Sound is Not a Fixed Number

Did you know that freezing temperatures actually make it easier for jets to break the sound barrier?

Mach 1 isn't a set speed; it’s a physical threshold dictated purely by temperature. On a warm day at sea level, you have to push a jet to 761 mph just to break the barrier. But modern fighters and commercial jets fly high up at 35,000 feet, where the air sits at a brutal minus 65 degrees Fahrenheit.

Cold air molecules are sluggish and lack energy, meaning sound waves cannot travel through them as quickly. Because of this freezing environment, the speed of sound drops significantly to just 660 mph. By climbing into the freezing stratosphere, aerospace engineers use the laws of thermodynamics to cheat physics and go supersonic with less effort.

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