1. Sound

2. What causes Sound? All sounds have one thing in common….
They are all created by VIBRATIONS!
A vibration is the complete back and forth motion of an object.

3. Sound Waves
Sound waves are LONGITUDINAL waves caused by vibrations and carried through a substance.
Sound travels in all directions away from the source.
Sound carries energy; NOT MATTER!

4. Detecting Sound How do we hear sounds? Watch this video to find out!
How Humans Hear!

5. Review Questions! longitudinal Sound waves carry energy, not matter!
Sound travels as a _____________________ wave.
Why wouldn’t a person at a rock concert feel gusts of wind coming from the speakers?
What do you call the area where particles are squeezed together here?
What do you call the area where particles are spread out?
5. Which part of the ear increases the size of the vibrations entering the ear?
Sound waves carry energy, not matter!
compressions
rarefactions
Middle ear

6. Properties of Sound!

7. Speed of Sound in Different Media
The speed of a sound wave depends ONLY on the medium through which it is traveling.
You would think that sound would travel faster through air, but that is not correct!
Watch this!
And this!
As always, sound CANNOT travel in a vacuum.
Sound is a mechanical wave that must have a medium!
Speed of Sound in Different Media
Medium
Speed (m/s)
Vacuum
Air (20°C)
343
Water (20°C)
1,482
Steel (20°C)
5,200

8. Pitch and Frequency
Reminder: Frequency is the number of waves per second.
Frequency is measured in Hertz (Hz)
How high or low a sound seems to be is called the pitch.
High frequency sounds have a high pitch.
Low frequency sounds have a low pitch.
Check it out here!

9. Table 2 Frequencies Heard by Different Animals
Frequency and Hearing
Humans cannot hear all frequencies of sound. The chart below compares human hearing to that of other animals.
Sounds that have a frequency too high for people to hear are called ultrasonic.
Table 2 Frequencies Heard by Different Animals
Animal
Frequency range (Hz)
Bat
2,000 to 110,000
Porpoise
75 to 150,000
Cat
45 to 64,000
Beluga whale
1,000 to 123,000
Elephant
16 to 12,000
Human
20 to 20,000
Dog
67 to 45,000

10. Loudness and Amplitude
Loudness is a measure of how well a sound can be heard.
Basically, how loud a sound is 
Loudness is different from pitch.
The amplitude of a sound wave determines how loud it is.
The higher the amplitude, the louder the sound.
If you hit a drum harder, you apply more energy and make the vibration larger. Therefore, the sound is louder!
Watch here!

11. How loud is too loud?
Table 3 Decibel Levels of Common Sounds
Decibel level
Sound
the softest sounds you can hear 20
whisper 25
purring cat 60
normal conversation 80
lawn mower, vacuum cleaner, truck traffic
100
chain saw, snowmobile
115
sandblaster, loud rock concert, automobile horn
120
threshold of pain
140
jet engine 30 m away
200
rocket engine 50 m away
Now you will do a Gizmo and find out more about pitch and loudness of sounds!

12. The Doppler Effect!

13. What is the Doppler Effect?
The Doppler Effect is an apparent change in pitch of sounds made by moving objects.
To get a better idea of what the Doppler Effect is, watch this!
Label the areas of high pitch and low pitch on your picture in your notes.
To see how we use the Doppler Effect, watch this!
Low Pitch
High Pitch