Consider three sound waves: A, B, and C.
• Wave B has a higher pitch than the other
• Wave C has the softest volume. Wave B
• Wave A and C have the same pitch.
• Wave A and B have the same volume.
Accurately sketch the three sound waves.
• Draw Waves A and C so that they
• Fire Truck
• Big Bang Theory
• Breaking Sound Barrier
• Sonic boom animation
Discussion Question 1
As a fire truck approaches a listener, what
happens to its sound waves, and what will you
a. Waves spread apart; Pitch goes down
b. Waves spread apart; Volume goes down
c. Waves get closer; Pitch goes up
d. Waves get closer; Volume goes up
Discussion Question 2
A fire alarm on the wall suddenly starts ringing. Is
this an example of the Doppler effect?
Challenge: Would the sound change if you
panicked, and started running towards the alarm?
Discussion Question 4
• Two fire trucks have sirens that emit waves of the same
frequency. As the fire trucks approach a person, the
person hears a higher frequency from truck X than from
truck Y. Which of the following statements about truck X
can be correctly inferred from this information
I. It is traveling faster than truck Y
II. It is close to the person than the truck Y
III. It is speeding up, and truck Y is slowing down.
(A) I only
(B) III only
(C) I and II only
(D) II and III only
(E) I, II and III
Discussion Question 3
• Refers to the change in pitch
of sound due to the motion of
the source or the listener
• If source and listener moving
towards each other, then the
pitch is _______.
• If the source and listener
moving away from each other,
the pitch is _______.
• Sound barrier broken
1947 by Chuck
• “Demon in the sky.”
• Today, NASA space
shuttle Mach 25
F-18 at Mach = 1.4, altitude = 35,000 ft, NASA Dryden, pilot: Ed
T-38 at Mach = 1.1, altitude = 13,700 ft, NASA Wallops.
• Object creating
Sonic Boom disturbance travels
faster than speed of
• Multiple overlapping
crests = constructive
Discussion Question 4
The four figures below represent sound waves emitted by a
source. Which picture(s) represent(s) a source moving at
less than the speed of sound?
E) more than 1
Discussion Question 5
• Did Chuck Yeager hear the Doppler effect from
the X-1’s engine when he exceeded mach 1?
• Did he hear a sonic boom?
(A) yes no
(B) yes yes
(C) no no
(D) no yes
Prepare to go outside.