Ch Waves & Sound II. The Nature of Sound  Speed of Sound  Human hearing  Doppler effect  Seeing with sound

What makes Sound? 1. Vibration: back and forth motion a.There can not be sound if there is not any vibration b.Most vibrations are too fast for you to see. c.Vibrations require energy— sound is a form of energy.

How does Sound Travel? 2. When something vibrates molecules in the air crowd together, then spread apart, causing sound waves to travel away from the vibrating object

A. Speed of Sound  344 m/s in air at 20°C  Depends on:  Type of medium travels better through liquids and solids can’t travel through a vacuum  Temperature of medium travels faster at higher temps

Sound Reflection and Absorption A.Reflected sound is called an echo. 1. The vibrations are reflecting back to you. B.Soft, air-filled objects absorb sound. 1. When sound is absorbed, you do not hear it because it is not reflected back to you.

B. Human Hearing sound wave vibrates ear drum amplified by bones converted to nerve impulses in cochlea

How do you hear sound? 1. Sound causes your eardrum to vibrate. The eardrum vibrates differently for each sound. 2.The bones of your ear begin to vibrate, beginning with the hammer, moves to the anvil, and finally the stirrup. 3.The sound energy passes to the inner ear. This causes the fluid in the cochlea to move. 4.The nerves then carry the message to the brain. 5. Your brain then tells you what the sound is.

 c c  Once upon the time ear  ZM ZM

Pitch 1. Pitch: how high or low a sound is a.The higher the pitch the more “squeezed” together the waves are b.The higher the pitch the higher the frequency c.The lower the pitch the lower the frequency

B. Human Hearing  Pitch  human range: ,000 Hz ultrasonic waves subsonic waves

B. Human Hearing  Intensity  volume of sound (how loud, how soft)  depends on energy (amplitude) of sound wave  measured in decibels (dB)

B. Human Hearing DECIBEL SCALE

C. Doppler Effect  Doppler Effect  change in wave frequency caused by a moving wave source  moving toward you - pitch sounds higher  moving away from you - pitch sounds lower

 Doppler effect  Y

C. Doppler Effect Stationary sourceMoving sourceSupersonic source same frequency in all directions waves combine to produce a shock wave called a sonic boom higher frequency lower frequency

D. Seeing with Sound  Ultrasonic waves - above 20,000 Hz Medical ImagingSONAR “Sound Navigation Ranging”

2.Making Sound  All sounds are made by vibrations.  Humans make sound waves by using their voice.  The human voice is also made by vibrations.  The source of sound in humans is the vocal cords.  Vocal cords — 2 thin, elastic, bands of tissue that vibrate to produce sound.

 The 5 most annoying sounds  PoY PoY  The best sound in the world  FFw FFw

 Can silence actually exist  HI  Why You Hate the Sound of Your Own Voice  hY

How do the vocal cords produce sound? 1.Air from the lungs flows through the windpipe and into the voice box (where the vocal cords are). 2. Then the air pushes the vocal cords apart making them vibrate. 3. The vibrations create a series of sound waves that exit through your mouth. 4. The change of shape of the vocal cords changes the sound and its pitch. 5. If you can’t talk because of a cold or laryngitis, it is because your vocal cords are swollen and inflamed.

Communication tools that use sound  Voice – allows you to communicate with others.  Morse Code – code for numbers and letters using sound  Sonar – a device that sends sound waves through water to measure or find something.  Animal sounds  Musical instruments