# Eli5: What is the sound barrier?

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Eli5: What is the sound barrier?

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It’s just a term for the speed of sound in whatever media you/the sound are traveling in. (Since the speed of sound is different in air than in water).

It’s not really a “barrier”, and you don’t really “break” anything when you pass the speed of sound. Those terms have just kinda been applied to it since it causes a sonic boom which sounds like something being broken through.

It is simply the speed of sound, there is no barrier, its more just a figure of speech.

Breakibg the sound ‘barrier’ is simply a cpmmon way to state “your velocity has increased to the point it now exceeds the velocity of a sound wave”.

There are some cool things that occur when this happens. An object will generate massive shockwaves as it passes this speed which generates a sonic boom, but there is no physical or engineering barrier.

It’s the speed of sound

it’s called that because aircraft experience a lot of drag when going next to that speed, and so it was thought it’s like a barrier you can’t pass, a maximum speed

It’s said that when an aircraft passes the speed of sound it makes a sonic boom and that’s the “barrier” “breaking” which might be another origin for the term except that’s not really how it works, a sonic boom is created whenever an object faster than sound moves through the air, the sound kinda bunches all up because it’s slower than the object and when it all comes in it at once, it sounds like an boom, it’s not an actual explosion, it just sounds like one

It isn’t a barrier per se. Imagine you’re driving a car at 70 kmph. There a another car driving beside you, also at 70 kmph. This means your relative velocity is 0, which you can get t by subtracting the target object speed (the other car) from your own speed. Theory aside, practically this looks like you aren’t moving in relation to the other car. the background moves, but the other car isn’t.

Now let’s say, your wife is giving birth and you need to rush to the hospital from your boring 9-5. You will now be driving at 100 mph. Now that other car will still be moving, but you will pass though it at one point. Because your relative velocity is not 0 anymore, it’s 30, because math.

Its the exact same thing with sound barrier. Sound travels in waves right? by the word “travel”, you must’ve figured out that it too has a velocity. That particular velocity is called the sound barrier. When they say “breaking the sound barrier”, they mean that you have gone faster than sound did at one point of time (and most probably continued to go faster cuz why not?). It is at that exact point when you went faster than sound is when they say you broke the sound barrier.

So where is sound and how do you know if you passed through it like that car? Well it’s an abstract answer. It’s everywhere at every point of space, realistically speaking. So sound is beside you, around you and under you at all times, just go faster than it and you’d enter mach speed.

Oh also, going faster than sound means you stop hearing anything. Because sound isn’t fast enough to reach your ears.

edit: this isn’t an exhaustive answer. I used certain terms like speed and velocity interchangeably to prove a simpler and unrelated point.

“Sound Barrier” is a name made up by people in the early post-WW2 era who were trying to understand why airplanes became uncontrollable at speeds near Mach 1, the speed of sound.
The actual explanation turned out to be the formation of small shock waves on the wing and tail. These, especially those on the tail, changed the balance of forces, often resulting in an unrecoverable pitch-down (called “Mach tuck”) and dive.
Design changes, in particular the all moving horizontal stabilizer, solved the problem.