Learning Object 5

1. Ao Lin (Daniel) Gong
L2C Blue
15-7: The Doppler Effect

2. Introduction
• Sonic Boom is a
French-American CGI
TV series, produced by
Sega.
• It’s a spin-off of the
popular Sonic the
Hedgehog video game
franchise which
features a blue
hedgehog named
Sonic that runs very
fast.

3. Background Information
• The reason why people call the hedgehog Sonic is
because his running speed in air is faster than that of
sound.
• Which creates a shock wave behind him and the
sound that associates with this is a sonic boom.

4. Conditions to Create a Sonic Boom (1)
• For the purpose of this presentation, we will use the formula of a
moving source moving towards a stationary receiver:
v = speed of sound in air
vs = speed of the source
• When v is less than vs (object moving slower than sound), the
waves emitted stack up one behind another without overlapping.
Eg. A source travelling slower than the speed of
sound to the right direction.

5. Conditions to Create a Sonic Boom (2)
• But when the speed of the source reaches the speed of sound
( v = vs ), the sound waves once emitted in front of the source will
now be all bunched up at the nose of the object.
• As a result, the pressure at the nose will be very intense and a
shockwave will be created:
• This will cause the stationary receiver to
not hear anything until the source arrives.
• The receiver will also hear a “thump” instead
of a pitch of sound as the source passes by.

6. Conditions to Create a Sonic Boom (3)
• Finally, a sonic boom is only created if the speed of the source is
greater than the speed of sound ( v > vs ).
• As a result, the source will now lead the sound waves that it
creates and it will pass by the stationary receiver before the
receiver can hear the sound it creates.
• In addition, the sound that the receiver
hears is actually a sonic boom, which is
an enormous amount of sound energy
due to the compressions of sound waves
along conical edge of the wave pattern.

7. Sonic Boom!
• Therefore, there will be a short time delay as Sonic passes by a
receiver before all the high pressure compressed sound waves reach
it at once, and the high pressure sound followed by a low pressure
sound will cause a loud BOOM to be heard.
• A sonic boom will sound just like an
explosion and due to its high pressure
regions, it may cause damages like
shattering glass windows of structures
as a supersonic source passes by.

8. Checkout these bad boys breaking
sound barriers 
• https://www.youtube.com/watch?v=-d9A2oq1N38
• https://www.youtube.com/watch?v=BHBevPYVzaY

9. References and Picture Sources
• the Physics Classroom:
http://www.physicsclassroom.com/class/sound/Lesson-3/The-Doppler-Effect-and-
Shock-Waves
• Wikipedia: http://en.wikipedia.org/wiki/Sonic_boom
• The Doppler Effect and Sonic Booms – Dan Russell, Grad. Prog.
Acoustics, Penn State:
http://www.acs.psu.edu/drussell/Demos/doppler/doppler.html
• Nelson Phys 101 Revised Custom Volume 1
• Photo courtesy of Dr. Dan Russell, Grad. Prog. Acoustics, Penn
State and various authors of pictures I’ve found on Google
Images.