Question: What is the Sound Barrier?

Oliver Gordon answered on 4 Mar 2019:

It’s not a real physical “barrier” that you can run into! It’s what we use to describe the speed of sound in air (about 350 metres per second, or around 200 times your height every second). It’s called a “barrier” because above it, it’s much harder to keep going at that speed. This is partly why planes like the Concord were such feats of human engineering.

You hear a little “boom” too when you pass it – this is what happens when you “crack” a whip.