I saw a photo in a two dollar shop the other day of a jet "breaking the sound barrier". It looked kind of like a donut of cloud around the centre of the aeroplane. Can anyone explain all this to me??
Martin Smith (Avatar)
That cloud is just water vapour condensing out of the air. It also doesn't always happen when the mach 1 is reached, also it can occur at much much lower speeds.
In fact if the relative humidity is quite high (e.g. almost fog conditions) you will see it occurring over the wings of normal aircraft.
The air over the top of the wing decreases in pressure and is adiabatically cooled. If the relative humidity of this now cooler air is 100% water will condense out of the air.
The noise you hear is from the shock wave cause by increasing the your velocity past the speed of sound. There is a pressure wave in front of a moving object, it gets more and more "squashed in" as the object gets faster and faster.