1. Sound Waves
Unit 6

2. Make the room totally silent
What can you still hear?
Air?
Wildlife?
Something smaller?

3. Type of wave Sound waves are longitudinal waves.
They can be transverse in some solids.
Wonder: how does sound hurt your ears? Why is there a delay before you hear some sounds?

4. Sound properties Sound waves depend on : 1. Speed
2. Intensity/Loudness
3. Frequency/Pitch

5. 01 02 03 speed Why is there a delay when you hear an echo?
In dray air at 20 degrees Celsius, sound travels at 342 meters per second! 02
Sound travels fastest in solids, slower in liquids, and slowest in gases. 03
speed

6. Speed of sound

7. Intensity & loudness
Intensity: the rate at which a wave’s energy flows through a given area.
Depends on:
A. amplitude
B. Distance from the source of the sound
If someone whispers in your ear it could be considered more intense than if someone shouts at you from across a field.

8. intensity Intensity is measured in decibels (dB).
Decibels: every 10- decibel increase means sound intensity increases tenfold.
Example:
A whisper has times more energy than the threshold. (10 twice over)

9. loudness Loudness is subjective to a person’s interpretation.
Loudness is a physical response to intensity.
Loudness depends on intensity but also the health of your ears!

10. Frequency & pitch
Frequency depends on how fast the source of sound is vibrating.
(like the strings on an instrument or your vocal chords)
Longer instruments produce lower frequencies because the wave is stretched out.

11. pitch Pitch is the frequency of a sound as you perceive it.
But, it does not depend on the wave’s frequency…
Low-frequency sounds we call “low pitch” and high frequency sounds we call “high pitch” but they also depend on human factors like your age and health of your ears.

12. ultrasound People hear between 20 and 20,000 Hertz
Ultrasounds use frequencies higher than 20,000 Hertz
Sonar: Sound Navigation and Ranging
Sends out a sound wave and waits for it to bounce back and return. Use math to calculate the distance of the object.
ultrasound

13. The doppler effect
Doppler Effect: change in sound frequency caused by motion of the sound source, motion of the listener, or both.
As the sound is closer, the person hears a higher frequency. As the sound moves away, the person hears a lower frequency.

14. music
Most instruments vary the pitch by changing the frequency of standing waves.
Resonance: the response of a standing wave to another wave of the same frequency.
Like constructive interference of two different sounds with the same frequency.