Introduction to Sound

1. Introduction to Sound Sound Waves, Pitch, and Loudness

2. How Does Sound Travel? • Sound waves are produced by vibrations. • Sound travels as longitudinal waves. • Sound waves travel in all directions.

3. Sound Waves, Medium, and Speed • Sound requires a medium. • Sound cannot travel in a vacuum. • When there is no air, there is no sound. • The speed of sound… • Changes when the medium changes. • Sound usually travels faster in denser media. • Depends on temperature. • Sound travels faster in warmer temperatures.

4. Sound Waves, Pitch, and Frequency • The pitch of a sound depends on the frequency of the sound wave. • High Frequency = High Pitch • Low Frequency = Low Pitch

5. What Frequencies Can We Hear? Humans can hear frequencies between 20 Hz - 20,000 Hz. Below 20 Hz – infrasonicAbove 20,000 Hz – ultrasonic • Younger people can generally hear higher frequencies; as you age, you lose the ability to hear high-pitched sounds.

6. Doppler Effect • The Doppler effect occurs when the source of the sound is moving relative to the listener. • Example: Police Siren • As the police car moves toward you, the siren has a higher pitch. • As the police car moves away from you, the siren has a lower pitch. Example Video

7. Sound Waves, Amplitude, and Loudness • The amplitude of a sound wave determines its loudness (or volume). • High Amplitude = More Energy = Loud Sound • Small Amplitude = Less Energy = Quiet Sound

8. Measuring Loudness • The loudness of a sound is measured in units called decibels (dB). • For every 10 dB, the intensity of the noise gets 10X louder. • Continued exposure to noise at 85 dB and higher cause hearing loss.

9. Quick Check Of the three graphs below, which sound has the highest pitch? Which is the loudest? Why?

11. Warm-Up Which sound wave has the highest pitch? Which is the loudest?