This document discusses sonic booms and the conditions needed to create them. Sonic booms occur when an object moves faster than the speed of sound in air. This creates shock waves that combine into a loud boom sound. For a sonic boom to occur, the object's speed must exceed the speed of sound. As it passes a stationary observer, they will hear the boom after the object passes, as the compressed sound waves reach the observer. Famous examples of objects breaking the sound barrier and creating sonic booms include supersonic jets and the fictional character Sonic the Hedgehog.

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.