1. Section 2: Properties of Sound
Chapter 2: Sound
Section 2: Properties of Sound

2. Discover Activity: How does amplitude affect Loudness pg. 42
1 volunteer is needed: rest of students take notes on this activity on the back of this packet.
Volunteer, take the pink harp (toilet seat) and pull back
one of the strings 1 cm to one side. This distance
is the amplitude of vibration. Let it go. How far
does the string move to the other side? Describe
the sound you hear.
Repeat Step 2 four more times. Each time, pull the string back a greater distance. Describe how the sound changes each time.
How would you define the amplitude of the vibration?
What effect did changing the amplitude have on the sound?

3. Loudness- describes your perception of the energy of a sound.
-describes what you hear
- the closer you are to sound the louder it is
A. The loudness of a sound depends on two
factors: the amount of energy it takes to
make the sound and the distance from
the source of the sound.

4. Energy of a Sound Source:
1. recall: the greater the amplitude of a wave, the
more energy the wave has.
2. Therefore: the greater the energy used to make
a sound, the louder the sound
Ex: pulling the string back farther generates a
louder sound
Distance From a Sound Source:
1. Why does loudness increase the
closer you are to a sound source?

5. 2. The closer the sound wave is to its source, the more energy it has in a given area. a. The total energy of the wave stays the same whether it is close or far from the source 3. intensity- the amount of energy a sound wave carries per second through a unit area Insert transparency 020

6. D. Measuring Loudness- 1. decibel- the unit used to compare the loudness of different sounds Ex: soft music = 30-dB Ex: whisper = 20-dB

7. A. The pitch of a sound that you hear
Pitch- of a sound is a description of how high or low the sound seems to a person.
A. The pitch of a sound that you hear
depends on the frequency of the sound
wave.
B. Pitch and Frequency-
1. high frequency = high pitch
a. 50 Hz = 50 vibrations per second
b. Most people hear sounds with
frequencies b/n 20-20,000 Hz

9. 3. infrasound- sounds with frequencies C. Changing Pitch-
2. Ultrasound - sound waves with
frequencies above the normal human
range of hearing
3. infrasound- sounds with frequencies
below the human range of hearing
C. Changing Pitch-
1. pitches are usually called notes
2. larynx- aka. the voice box
part of the throat that contains the
vocal cords

10. a. Air from the lungs is forced up the trachea past the vocal cords causing vibration 1. result = sound waves 2. vocal cords can vibrate more than 1,000 times per second 3. tight vocal cords = higher pitches 4. same applies to guitar string, tighter stings = higher frequency = higher pitch

11. The Doppler Effect:
A. The Doppler Effect- is the change in frequency of a wave as its source moves in relation to an observer.
Ex: Fire truck and siren:
1. sound stays the same for the firefighters in
the truck
2. pitch of the siren drops as the truck passes
an individual

12. B. Causes of the Doppler Effect –
1. When a sound source moves, the frequency of
the waves changes because the motion of the
source adds to the motion of the waves.
C. What Causes Shock Waves?
1. sound waves pile up as plane travels
almost as fast as speed of sound.
a. pile up of waves is the “sound barrier”
b. A shock wave forms as the sound waves
overlap.
1. shock wave releases a huge amount
of energy heard as a sonic boom