When some object moves faster than the speed of sound —thus supersonic— it arises a really curious effect for any listener. A lightning strike occurs luckily at some distance, and the sound has a lag that is useful for calculating the distance. In the case of an object traveling at supersonic speed, what do you listen if it is in your exact position? This phenomenon is called the Doppler effect, and the listener doesn't perceive the sound source until after, proportional to the velocity. Mach 1 is one time the speed of sound, mach 2 twice and so on. There's also another velocity called hypersonic, after mach 5.
The sonic barrier was understood pretty close in time, even when objects like whips or projectiles launched with “gunpowder” did make a characteristic noise. In the case of planes, the effect is more perceivable as it mixes another, visual this time.
In the first times, breaking the sound barrier did create an additional risk for aircraft, with some of them being destroyed. Fortunately, the “barrier” was disappearing with time!
With hydrocarbons, the mach 1 feat is considerably easy for the engineering field. Although, what about electric vehicles?