What is the white fog around the Ares rocket after takeoff?

The sound barrier is a physical phenomenon. When an object (usually an aircraft) approaches the speed of sound, it will gradually catch up with its own sound waves. Due to the superposition and accumulation of sound waves, shock waves will be generated, which will further hinder the acceleration of the aircraft. This obstacle caused by the speed of sound is called the sound barrier. After breaking through the sound barrier and entering the supersonic speed, a conical sound cone will be produced from the front end of the aircraft. This kind of shock wave sounds like an explosion to onlookers, so it is called sonic boom. A strong sonic boom will not only damage buildings on the ground, but also damage the part of the aircraft itself that extends beyond the impact surface.

In addition, when the speed of an object approaches the speed of sound, the surrounding air is superimposed by sound waves, showing a very high pressure state, so once the object crosses the sound barrier, the surrounding pressure will drop sharply. In humid weather, sometimes the instantaneous low temperature caused by the sudden drop of pressure may make the temperature lower than its dew point temperature, and make the water vapor condense into tiny water droplets, which looks like a cloud to the naked eye. However, because this low pressure zone will return to normal pressure with the increase of the distance between the air and the fuselage, it looks like a cone cloud with the object as the central axis and spreading evenly around.