Here's what that means:

* Mach number is a unit of measurement for speed that compares an object's speed to the speed of sound.

* Mach 1 is equal to the speed of sound, which varies depending on factors like temperature and altitude.

* At sea level and standard temperature (15°C or 59°F), the speed of sound is approximately 767 mph (1,235 km/h).

Therefore, an object needs to reach at least 767 mph (1,235 km/h) to break the sound barrier.