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

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

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

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

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

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??

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

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.

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.

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

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)