Raeleen Breaking the sound barrier

http://www.scientificamerican.com/article/what-happens-when-an-airc/   (simplified)

What happens when an aircraft breaks the sound barrier?

Mar 11, 2002.

What happens when an object breaks the sound barrier must begin with the description of sound as a wave.  Anyone who has heard an echo (sound waves reflecting off a distant surface) or been far enough away from an event to see it first and then hear it, is familiar with the reasonably slow travel of sound waves. At sea level and temperatures of 22 degrees Celsius, sound waves travel at 345 meters per second. As the temperature decreases, the sound speed also decreases, so for a plane flying at 35,000 feet (10688 metres) where the temperature is  around -55 degrees Celsius, the speed of sound is 295 meters per second.

When the sources of a sound is moving it can begin to catch up with the sound waves they emit. As the speed of the object increases to the speed or velocity of sound waves, these sound waves begin to pile up in front of the object. If the object has sufficient acceleration, it can burst through this barrier of sound waves and move ahead of the sound it is making. As the object outruns all the pressure and sound waves in front of it, it is heard on the ground as an explosion, or sonic boom.

At supersonic speeds (those greater than the speed of sound), there is no sound heard as an object approaches an observer because the object is traveling faster than the sound it produces. Only after the

“?:object has passed will the observer be able to hear the sound waves emitted from the object.

Aircraft wings create low-pressure regions. Under sonic flight conditions the lowered pressure condenses the water in the air, creating a vapour cloud. Just as the aircraft bursts through the sound barrier, the air is locally disturbed by the resulting shock wave and the condensation/vapour cloud disappears.

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What is an echo?

A sound that is caused by the reflection it bounces of an object then it goes to the listener.

What happens to the sound waves, when the object making the sound is moving?

The sound waves begin to pile up in front of the object.

Why is there no sound heard as an object approaches if it is going at supersonic speed?

Because the object is travelling faster than the sound it produces.

What does supersonic mean?

Involving a speed greater that of sound

Why does a person travelling in a car with the horn sounding only hear one pitch whereas someone listening to the car drive past and hears the pitch change as they drive past?

Because the car horn only can make one noise which is a high pitch.

What does decrease mean?

Sufficient? Private Income

Emit? Gas or radiation

Velocity? A speed of something in a given direction

Condense? Something density or more concentrated

acceleration? A viachle capacity to gain speed