1. Why are some sounds high and some sounds low??
The differences between the sounds—how high or low and how loud or soft they are—depend on the properties of the sound waves

2. The Speed of Sound Depends on the Medium
I can talk underwater
The time it takes for sounds to reach you does not depend on how loud or high the sound is.
The speed of sound depends only on the medium through which the sound is traveling

3. The Speed of Sound Depends on the Medium
Speed of Sound in Different Media at 20 degrees Celsius
The time it takes for sounds to reach you does not depend on how loud or high the sound is.
The speed of sound depends only on the medium through which the sound is traveling
Medium
Speed m/s)
Air
343
Helium
1,005
Water
1,482
Sea Water
1,522
Wood (oak)
3,850
Glass
4,540
Steel
5,200

4. In general, the cooler the medium, the slower the speed of sound
This happens because particles in cool materials move slower than particles in warmer materials
When the particles move slower, they transmit energy more slowly
Therefore, sound travels more slowly in cold air than in hot air

5. Pitch Depends on Frequency
The pitch of a sound is determined by the frequency of the sound wave
The higher the frequency the higher the pitch

6. Frequency and Hearing Why can’t you hear a dog whistle??
Because the frequency of the sound wave is out of the range of human hearing
Did you hear that??

7. The average human ear can detect sounds that have frequencies between 20Hz and 20,000Hz.
Young children can often hear sounds with frequencies above this range, while many elderly people have difficulty hearing sounds higher than 8,000Hz 
Range of hearing in Hertz

8. Ultrasound
Ultrasound is sound of vibrations with frequencies too high to be audible by the human ear, above approximately 20 kilohertzs or 20,000Hz.
Ultrasound has industrial and medical applications. Medical ultrasonography can visualize muscle and soft tissue, making them useful for scanning the organs. However, they will not penetrate bone so they are not a substitute for conventional X-rays in many cases.
Ultrasonic cleaners, sometimes called supersonic cleaners, are used at frequencies from 20-40kHz for Jewelry, Lenses, Optical parts, Watches, Dental instruments, surgical instruments, and industrial parts.

9. Loudness is Related to Amplitude
If I strike a drum with a large force, I will hear a loud BOOM!!
Changing the force I strike the drum will change the loudness of the sound that is created
Loudness is how loud or soft a sound is perceived to be
As you strike the drum harder, you transfer more energy to the drum
The drum moves with a larger vibration and transfers more energy to the surrounding air
This increase in energy causes air particles to vibrate farther from their rest positions.

10. When you strike a drum harder, you are increasing the amplitude of the sound waves being created
The amplitude of a wave is the maximum distance the particles in a wave vibrate from their rest positions.
The larger the amplitude, the louder the sound, and the smaller the amplitude, the softer the sound
An amplifier increases the amplitude of the sound generated by my guitar

11. Measuring Loudness Some Common Decibel Levels Sound Decibel level 20
The softest sounds you can hear
Whisper 20
Purring cat 25
Normal conversation 60
Lawn mower, vacuum cleaner, truck traffic 80
Chain saw, snowmobile
100
Sandblaster, loud rock concert, automobile horn
115
Threshold of pain
120
Jet engine 30 meters away
140
Rocket engine 50 meters away
200
The most common unit used to express loudness is the decibel (dB)