2. How Sounds Are Made What happens when a bell shakes or a drum moves up and down? Vibrations occur – sound is produced when matter vibrates Remember: sound travels as a longitudinal wave

3. Talking About Sound When you talk, air moves from your lungs over your vocal cords, causing them to vibrate. As your vocal cords move inward, the air between them is pushed together, creating a compression. As your vocal cords move outward, less particles of air are left, creating a rarefaction.

4. Speed of Sound Speed depends on the medium, NOT the source. Speed of sound is determined by: 1. Temperature 2. Elasticity 3. Density

5. Temperature Lowering the temperature, makes the motion of the particles more sluggish. The particles have a more difficult time of moving and returning to their original positions. Sound travels SLOWER at lower temperatures and FASTER at higher temperatures.

6. Elasticity and Density Sound waves travel through any medium. Native Americans use to put their ears to the ground to find out if buffalo were nearby. WHY? Sound travels about 4 times faster in the ground than in the air. Sound travels fastest in solids and slowest in gases. Think about walking in sand: you have to put in a lot of energy to step. Sound is the same. In less-static mediums (like air or water), the waves travel slower. Solids are usually more elastic. Would sound travel faster in water or air?

7. Elasticity and Density (Continued) Waves travel the FASTEST in solids and the SLOWEST in gases. GASES LIQUIDSSOLIDS air water lead Heliumsalt water brick milk stone

8. Properties of Sound Frequency-number of waves that pass a certain point in a certain amount of time Frequency is measured in Hertz (Hz). ______________ Hz_________________ Hz

9. Frequency (continued) http://www.youtube.com/watch?v=HpovwbPGEoo http://library.thinkquest.org/19537/java/Beats.html As the frequency increases, the number of waves increases.

10. Pitch – a description of a sound as high or low, which depends on the frequency of waves Sound waves with a high-frequency have a high pitched sound, like a flute A bass drum has a low frequency, so it produces a low pitch Humans can hear sounds between 20-20,000 Hz.

11. Doppler Effect http://www.youtube.com/watch?v=Kg9F5pN5tlI http://www.lon-capa.org/~mmp/applist/doppler/d.htm

12. Doppler Effect (continued) Doppler Effect – change in sound or light that occurs whenever there is motion between the source and its observer The pitch of the siren is higher as it approaches you and lower when it moves away from you.

13. Intensity and Loudness Intensity Amount of energy carried by a wave in a certain amount of time The larger the amplitude, the greater the intensity Intensity is measured in decibels

14. Interference Constructive Destructive When sound waves combine to create a greater disturbance When sound waves combine to make a wave that is less than either wave alone

15. Applications of Sound Sonar Ultrasonic Cleaning Sonar: Sound Navigation And Ranging Bats send out high-frequency sound waves, which bounce off objects and reflect back as echoes. Bats use echoes to navigate or find their next meal. Sonar is also used in commercial fishing, in cameras to focus, and in cars to warn of nearby objects. Ultrasonic waves are used to clean jewelry, electronic components, and delicate machine parts. Sound waves are sent through the liquid and the vibration knocks off the dirt.

16. Applications of Sound (continued) Sound and Medicine Ultrasonic waves are used to diagnose medical problems. Similar to sonar Ultrasonic waves may be used to treat medical conditions by destroying unwanted tissue

17. How You Hear 1. Sound waves enter the outer ear, which acts as a funnel. 2. The waves move through the ear canal. 3. The waves hit a lightly stretched membrane called the eardrum. The eardrum vibrates. 4. The vibrations hid the middle ear, which consists of three small bones.

18. How You Hear (continued) 5. The hammer, anvil, and stirrup send the vibrations along. 6. The vibrations hit the liquid-filled inner ear. 7. The vibrations move to the snail-shaped cochlea. 8. The cochlea has hundreds of nerve fibers which convert the sound into an electrical impulse that is sent to the brain.