1. Sound
Ch 13.1 – 13.2

2. Sound Waves Sound waves mechanical
produced by vibrating objects
longitudinal
mechanical
As objects vibrate, a series of compressions and rarefactions are created
a compression is the region of a longitudinal wave in which the density and pressure are greater than normal
A rarefaction is the region of a longitudinal wave in which the density and pressure are less than normal

3. Sound Waves
Longitudinal Wave
Vibration of Sound Source

4. Speed of Sound Waves
The speed of a sound waves depends partially on three things:
Material
vair < vhelium < vhydrogen
Phase
vsolid > vliquid > vgas
Temperature
vair,0°C < vair, 25°C < vair, 100°C

5. Speed of Sound in air vsound = 331.5 + 0.6T T is temp in °C
Example: to find the speed of sound in air at 63°C
vsound = (63) = m/s

6. Example
You are in a canyon when you shout your name. You hear an echo 2 s later. If it were 20°C, how far away is the nearest canyon wall?

7. Sound Waves
audible sound waves are the waves the average human can hear 20 < f < 20,000 Hz
f < 20 Hz are called infrasonic
f > 20,000 Hz are called ultrasonic
pitch is the perceived highness or lowness of a sound
pitch is determined by the freq. of the wave
high freq. = high pitch
low freq = low pitch

8. Ultrasonic Waves Medical applications of Ultrasonic Waves Sonograms
Ultrasonic waves used to produce images of objects inside the body
Break up Kidney stones
vibrations of the waves cause stones to break apart and pass through excretory system

9. Sound waves Sound waves propagate in 3D
concentric circles are used to depict the center of compressions (wave front) of a sound wave
the distance between adjacent wave fronts is = to one wavelength

10. Sound Waves For a stationary object that is emitting sound waves…
The distance between each circle represents the wavelength. Tighter circles means shorter wavelength and higher frequency and pitch

11. 13-1 Doppler Effect For a moving object that is emitting sound waves…
VIDEO
13-1 Doppler Effect
Sonic Booms
For a moving object that is emitting sound waves…
shorter λ = higher freq.
longer λ = lower freq.
higher freq. = higher pitch
lower freq. = lower pitch
In Front
Behind

12. STOP

13. 13-2 Resonance Resonance Natural Frequencies
Frequency of vibration determined by the physical parameters of the vibrating object
Resonance
a condition that exists when the frequency of a force applied to a system matches the natural frequency of vibration of the system
Increases the intensity & amplitude of the sound

14. Harmonics
Fundamental Frequency - the lowest frequency of vibration of a standing wave.
Harmonics are multiples of the fundamental frequency

15. Calculating Harmonic Number
In a pipe open at both ends
fn = n v
n = 1, 2, 3, . . . 2L
Frequency = harmonic number x
(speed of sound in the pipe)
(2)(length of vibrating air column)