If an airplane is flying faster than the speed of sound,



It will produce a sonic boom or shock wave.

As shown in the right figure,

consider an airplane which is flying from A toward B.
A listener is located at C.

The sound generated at A travels toward C along the path AC.

The listener hears the sound as the airplane flies toward point B. ( AB > AC )

DC is the path of the sound generated at D to the listener.

The airplane speed is V and the sound speed is Vs.

If AC/Vs > AD/V + DC/Vs

[Isn't it unlikely that the shorter path will take a longer time?]
, then the sound generated at point D will arrive earlier than sound generated at point A!

Funny! You hear something which happened later and then hear something which happened earlier !

What will you hear if a supersonic airplane flying over you?

Do you know where is the airplane when you hear it?

Can you point out the direction of the airplane just from hearing the sound?

This java applet let you play with such situation.

How to play¡G

Press Start to start the animation. A listener is represented by an ear!

You can press the left mouse button and drag it within the screen

to change location of the listener.
The program draws sound wave paths to the listener.

The animation will be suspended when the sonic boom arrives at the listener.

Click the right mouse button to continue.

The color of the paths changes to blue.

The order in which the sound paths arrive at the listener are shown also.

You can change the ratio of airplane speed of airplane to sound speed and see the difference.

Press Reset for default values.

Your suggestions are highly appreciated! Please click hwang@phy03.phy.ntnu.edu.tw

Author¡GFu-Kwun Hwang, Dept. of physics, National Taiwan Normal University