1. Conceptual Physics
Notes on Chapter 26
Sound

2. Sound All sounds are produced by the vibrations of material objects.
Pitch describes our impressions about frequency or sound when produced by vibrations.

3. NOTE: No human can hear above or below 20 - 20000 hertz.
Sound
A “normal” person can distinguish sound frequencies between 20 and 20,000 hertz.
below 20 hertz is known as infrasonic.
above 20,000 hertz is known as ultrasonic.
NOTE: No human can hear above or below hertz.

4. Sound
When something vibrates, it causes a wave that compresses and stretches.
In physics we call this Compression and Rarefaction.

5. Sound
Sound needs a medium to travel through. But sound travels at different speeds in different mediums.
Air --- can range from 330 m/s m/s
NOTE: For ALL problems we will take the average speed of 340 m/s
Liquid - can range from 1325 m/s m/s
NOTE: For water we will take the average speed of 1360 m/s (Water)
Solid - Can range from 4500 m/s m/s
NOTE: For solids we will take the average speed of 5100 m/s (Steel)

6. Sound
LOUDNESS
Loudness is subjective. Each person hears sound different due to each persons brain interrupts sound different.
Sound intensity is objective and is measured in decibels (dB). Decibels are based on a logarithmic variation.
EX: 40 dB is 100 times as loud as 20 dB
100 dB is 10 times as loud as 90 dB
See Table 26.1 Pg. 519

7. Sound
A natural frequency is the frequency at which an object vibrates when it is disturbed
Different objects create different sound waves.

8. Sound
Forced vibration is when a vibrating object causes a object in contact with it to also vibrate.

9. Sound
Resonance is a phenomenon when the frequency of a vibration forced on an object matches the object’s natural frequency and a dramatic increase in amplitude occurs.

10. Sound Interference of sound waves affects the loudness of sounds.
Constructive interference makes sounds louder.
Destructive interference result in fainter sounds or no sound at all.

11. Sound
BEATS
Beats happen when two waves interfere with each other in a way that some of the wave energy overlaps constructively and some overlap destructively.

12. Sound
If you subtract the frequencies of the two tuning forks, you can get the beat frequency.
EX: 262 Hz and 266 Hz
262 Hz and 272 Hz