Sonic Boom

It is widely known that a sonic boom is created when an object passes the sound barrier. But what many don't realise is the boom is continueous for as long as the object is supersonic, not just when the sound barrier is first broken.

Take a supersonic plane. This plane is in a 'soup' of particles which we call air, (air is actually more like soup than just a few particles whizzing around, which is what is taught in schools :/ ). As the plane moves through the air, the soup of particles at the front move out the way. The faster the plane travels, the faster the particles have to move out the way. But the particles can only move at around 340 metres per second and stay happy, which is why sound can only move at that speed, since sound it is simply particles moving.

So the most a plane can move and keep the particles happy is around 340 m/s. At this speed, the particles start to build up at the front of the plane, since they can't move away fast enough. For the plane to go faster, it needs to pierce through this build up. Planes with normal wings and tail would at this point have their rudders and flaps jammed due to the immense force now being emitted by the particles trying to hold back the plane.

This is why supersonic planes are extremely streamline, and why in early designs, instead of just some flaps and rudders moving, the entire wing and tail move. This prevents jamming as there are no flaps to jam.

The sound it created when this 'barrier' is broken through and the particles are forced to move out the way at a speed that is faster than what they're comfortable with.

Now that the plane has pierced the sound barrier, it needs to continue to pierce it because particles are still there up front. This produces a continues sonic boom, which is heard as long as the plane is supersonic speed.

The Concord only went supersonic over the sea for this reason, otherwise any windows that were in the flight path were likely to be smashed.