# Frequency of Sound

```Sound Guided Notes
Name:___________________ Class: ______
Do Now
Define the following terms, giving units and variables for 5-8.
1. Wave ____________________________________________________________________________________
__________________________________________________________________________________________
2. Longitudinal wave ___________________________________________________________________________
__________________________________________________________________________________________
3. Transverse wave ___________________________________________________________________________
__________________________________________________________________________________________
4. Mechanical wave ___________________________________________________________________________
__________________________________________________________________________________________
5. Frequency _________________________________________________________________________________
__________________________________________________________________________________________
6. Wavelength ________________________________________________________________________________
__________________________________________________________________________________________
7. Pitch _____________________________________________________________________________________
__________________________________________________________________________________________
8. Amplitude _________________________________________________________________________________
__________________________________________________________________________________________
The nature of sound
What kind of waves are sound?
 ___________________ - caused by oscillations of atoms
 ____________________ - creates areas of high and low pressure
What are areas of high pressure called?
What are areas of low pressure called?
Frequency of Sound
• The frequency of sound refers to the ___________________________________________ made by atoms, and
it is measured in ______________ (s-1).
•
Frequency = ________________
•
Human ear can hear between 20 – 20 000 Hz.
•
•
_________________ – below 20 Hz
•
_________________ – above 20 000 Hz
Bats and dolphins use ultrasound for navigation; elephants and whales communicate over large distances using
infrasound.
Loudness of Sound
Which variable do you think corresponds to the loudness of sounds?
Loudness is measured on a decibel scale
Speed of Sound
Speed of sound depends on …
________________________________________________________.
________________________________________ (though high frequency
waves will have short wavelengths and low frequency waves will have
high wavelengths in accordance with λf = v )
Sound is typically fastest in solids, then in liquids, and slowest in gases.
Sound is faster in warm, humid air than in cold, dry air.
Doppler Effect
The _____________________________________________________ that occurs when the _____________________
________________________________________________________________________________________________.
Represents a stationary sound source
The distance between wave fronts is the wavelength.
All observers will hear the _______________
Represents a source moving at v
Wave fronts are still produced with the same frequency but
are bunching up in the direction of travel
Observer in front of the source hears a _________________
sound
Observer behind the source hears a ____________________,
lower frequency sound.
This is called a ______________________________.
.
General Rule:
If the source and the observer are moving
… closer together  the perceived frequency is ______________
... farther apart  the perceived frequency is ________________
Doppler Effect Applications
Doppler shift can be used to determine the relative speed of objects. Waves are directed at an object, they reflect
(bounce back) and are picked up by a receiver. The ____________________________________________________
___________________________________________________.
Examples:
ultrasound waves to show blood velocity