Chapter 14: Sound

Sound is…

O http://www.youtube.com/watch?v=MFLeG

JclQiI&feature=related

Watch the video and take down 3 key

points about sound

Longitudinal Waves and guitar

O http://www.physicsclassroom.com/mmedia/waves/gsl.cf

m

O http://illuminations.nctm.org/ActivityDetail.aspx?ID=37

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?

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.

Bell Jar experiment

O http://www.youtube.com/watch?v=ce7AMJ

dq0Gw

What does the video tell you about how sound travel?

O Compressions and rarefactions propagate faster in denser

medium

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.

15.1 Sound Waves

Solid Liquid Gas

Speed of soundHigh Low

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)

Pitch and Frequency

O

The higher the frequency of the sound

wave,

the higher the pitch of the sound.

Loudness and Amplitude

O

The higher the amplitude of the sound

wave,

the louder the sound.

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?

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?

Application of echo

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)

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?