Unit 5 Waves

1. Unit 5Waves Ch. 21 Sec. 1 & 2 What is Sound?

2. Sound Waves • sound - a compressional wave caused by vibrations that make air molecules move back & forth • a sound wave is a series of compressions (dense air molecules) & rarefactions(spread out air molecules) • speed of sound is… • fastest through solids • slowest through gases • faster at high temps. • slower at low temps.

3. Human Ear • 3 Main Parts: • outer ear - collects sound • middle ear - amplifiessound when vibrations of the eardrum are passed to 3 small bones • inner ear - convertssound when vibrations are passed to cells in the cochleaand then create nerve impulses which travel to the brain • disease, age, & exposure to loud sounds damage hearing

4. Intensity & Loudness • loudness - human perception of the energy in a sound wave • represented by the decibel (dB) scale • more energy = higher amplitude = louder • http://www.animations.physics.unsw.edu.au/jw/sound-pitch-loudness-timbre.htm

5. Frequency & Pitch • pitch - how high or low a sound seems • high frequency = high pitch [direct relationship] • shorter, thinner vocal cords = higher pitch • http://www.animations.physics.unsw.edu.au/jw/sound-pitch-loudness-timbre.htm

6. Echoes • echo - a sound wave reflected off a hard surface • can be used w/ sonar to map the ocean floor • can be used w/ echolocation to navigate & hunt

7. The Doppler Effect • Dopplereffect- change in frequency that occurs when a sound source or listener is in motion • ex. as a siren approaches, higher frequency causes a higher pitch • ex. as a siren passes, lower frequency causes a lower pitch • http://www.stmary.ws/highschool/physics/home/animations3/waves/DopplerEffectTrain.html

8. Using Sound in Medicine • sound waves can be used in medicine… • can view body parts • ultrasounds can destroy kidney stones • can view developing fetuses