1. Characteristic Review and Propagation
Sound Waves
Characteristic Review and Propagation

2. Sound Waves
What are they?
Longitudinal
Require medium

3. Production
Compression- region of a longitudinal wave in which the density and pressure are greater than normal (crests)
Rarefaction- region of a longitudinal wave in which the density and pressure are less than normal (troughs)

4. Characteristics of Sound Waves
Frequency- the # of cycles per unit of time
Audible: 20 – 20,000 Hz
Infrasonic: less than 20 Hz
Ultrasonic: more than 20,000 Hz

5. Characteristics of Sound Waves
Frequency determines pitch
Frequency is a quantity of sound that can be measured
Pitch is how different frequency are perceived by our ears
Increase in frequency = Increase in pitch

6. Resonance (Frequency)
Click below to watch the Visual Concept.
Visual Concept

7. Speed of Sound Sound waves travel though solids, liquids and gases.
In which would the speed generally be greatest? Why?
Solids. Because the molecules are more closely packed, the particles respond more rapidly to compressions.
How might the temperature of air affect the speed of sound waves? Why?
Higher temperature increases the speed of the waves because the particles are moving faster and colliding more often.

8. Speed of Sound

9. Characteristics of Sound Waves
Propagation
Travel in all three dimensions
Wave Fronts- indicate center areas of compression
Rays- indicate direction of waves, perpendicular to the wave fronts
Plane waves

10. Spherical Wave Sound propagates in three dimensions.
The diagram shows:
Crests or wave fronts (blue circles)
Wavelength ()
Rays (red arrows)
Rays indicate the direction of propagation.
How would these wave fronts appear different if they were much farther from the source?

11. Spherical Wave
Wave fronts and rays become more nearly parallel at great distances.
Plane waves are simply very small segments of a spherical wave a long distance from the source.

12. Doppler Effect
Motion creates a change in frequency
Why?

13. Doppler Effect Why are the waves closer together on the left?
Waves are closer because the vehicle moves to the left along with the previous wave.

14. Doppler Effect and Sound
Click below to watch the Visual Concept.
Visual Concept

15. Question 1 What is the difference between pitch and frequency?
Frequency measures particle vibration and pitch is subjective to the listener

16. Question 2
Why does the speed of sound depend on the temperature of the medium. Why is this temperature dependence more noticeable in a gas that in a solid or liquid?
Molecules that have more motion (higher temps) transfer their vibrations more easily. This is less noticeable in liquids and solids because the particles are closer together.

17. Question 3
A bat flying towards a wall emits a chirp at 40 kHz. Is the frequency of the echo received by the bat greater, less than, or equal to 40 kHz? Why?
Greater than