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Wisdom consists of the anticipation of consequences. ..."Norman Cousins(1913-1990, American author)"

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 Author Topic: The location of supersonic airplane  (Read 115342 times) 0 Members and 1 Guest are viewing this topic. Click to toggle author information(expand message area).
Fu-Kwun Hwang
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 « Embed this message on: January 29, 2004, 08:13:09 pm »

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### The location of supersonic airplane.

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 flys 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.
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.

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 « Embed this message Reply #1 on: January 30, 2004, 11:02:11 am »

Quote
Date: Mon, 29 Jun 1998 15:30:54 EDT
From: Jrice45515@aol.com
To: hwang@phy03.phy.ntnu.edu.tw
I have taken the liberty of making some minor wording changes so that your description will be more grammatically correct.
I wish I were multilingual as you are! ;-)
The location of supersonic airplane.
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 flys 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.
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.
John Rice

Thank you John. I have modified the above message with your version.
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Wisdom consists of the anticipation of consequences. ..."Norman Cousins(1913-1990, American author)"