Eli5: What is the sound barrier?
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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.
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