What is the sound barrier?
Breaking the sound barrier means exceeding the speed of sound at 12,192 metres (40,000 feet), that’s about 1,062 kilometres per hour (660 miles per hour).
When Chuck Yeager broke the sound barrier with the Bell X-1 rocket plane in 1947, his mum wasn’t mad. This was one case where breaking something was a good thing. The sound barrier is simply the point an object exceeds the speed of sound – a speed many scientists once considered impossible.
Sound is a travelling wave of pressure. A moving object pushes nearby air molecules, which push the molecules next to them, and so on. As a plane approaches the speed of sound, its pressure waves ‘stack up’ ahead of it to form a massive area of pressurised air, called a shock wave. Shock waves would shake old planes violently, creating an apparent ‘barrier’ to higher speeds.
You can hear shock waves as sonic booms. Sometimes they’re even visible: the high pressure area can cause water vapour to condensate into liquid droplets, briefly forming a cloud around the plane.
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