2. Sound is…
Watch the video and take down 3 key
points about sound
O http://www.youtube.com/watch?v=MFLeG
JclQiI&feature=related
3. Longitudinal Waves and guitar
Watch the video and answer the questions:
(1) How did the air layers get into vibration?
(2)Did the air layers move with the sound wave?
(3) How did the air particles move relative to the
direction of the sound wave?
O http://www.physicsclassroom.com/mmedia/waves/gsl.cf
m
O http://illuminations.nctm.org/ActivityDetail.aspx?ID=37
4. Production and
Propagation of Sound
O Sound is produced by vibrating sources
in a medium.
O The source cause the air particles to
vibrate and the sound wave will
propagate outwards in the form of a
longitudinal wave.
O When air particles are pulled together, a
region of compression is formed. When
they are pushed apart, a region of
rarefaction is formed.
5. Bell Jar experiment
What does the video tell you about how sound travel?
O http://www.youtube.com/watch?v=ce7AMJ
dq0Gw
6. 15.1 Sound Waves
O Compressions and rarefactions propagate faster in denser
medium
High Speed of sound Low
Solid Liquid Gas
O Speed of sound in air is about 330 m/s in air,
1500 m/s in water, 5000 m/s in metal.
Qn: Why does sound travel faster in solid than in gas?
O Sound cannot travel in vacuum because there are no
particles to transmit the vibration.
7. Pitch of Sound
O Watch the video and answer the
questions below
O (1) how does the pitch change when the
frequency of the sound wave change?
O (2) what is the maximum frequency you
can detect?
http://www.youtube.com/watch?v=4nUkNvl8mQw
O Human audible frequency is between 20
Hz to 20 000 Hz (or 20 kHz)
8. Pitch and Frequency
O
The higher the frequency of the sound
wave,
the higher the pitch of the sound.
10. A B
C D
Which sound or sounds has/have
(a) the same pitch as A?
(b) the same loudness as A?
(c) the same pitch as B?
11. Echo
O Echo is caused by the reflection of sound from
a hard and flat surface like a wall or cliff.
O Why can’t you hear the echo when you clap
your hands next to a high wall?
13. Use of Echo to determine distance
O A man stands at the end of a long wall
and claps his hands. If he hears his echo
after 2 seconds, what is the length of the
hall? (Take the speed of sound in air to be
300 m/s)
14. Use of Echo to determine distance
O A ship transmits a pulse of sound into the
water and the receiver receives the
reflection of the sound by a shoal of fish
after 0.15 seconds. If the speed of sound
in water is 1200 m/s, how far is the shoal
of fish from the ship?
