1. Vibrations through a medium
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SOUND
Vibrations through a medium

2. Sound PITCH = The impression about the frequency of a sound
All sounds are produced by the vibrations of material objects.
PITCH = The impression about the frequency of a sound
high pitched – high frequency (ex: piccolo)
low pitched – low frequency (ex: fog horn)

3. Frequency
The average frequency range for normal human hearing is between 20 Hz and 20,000 Hz (for younger people; older people lose the higher frequencies).
Infrasonic or subsonic = Sounds below 20 Hz
Ultrasonic = frequencies above 20,000 Hz

4. Sound in Air
Longitudinal or Compression waves travel through air or along springs.
These waves travel with areas of compression and rarefaction
The medium does not travel from one place to another, but the pulse/energy travels.

5. Speed of Sound The speed of sound in dry air at 0C is about 330 m/s.
For each degree above 0C the speed of sound increases by 0.60 meters per second.
Sound travels 15 times faster in steel than air and about 4 times faster in water than air.
Any matter will transmit sound, whether it is a solid, liquid or a gas.
Sound cannot travel through a vacuum (it is a mechanical wave)

6. Intensity Intensity is the rate of energy flow through an area.
The unit of intensity for sound in the decibel (dB).
Sound intensity is objective and is measured by instruments such as an oscilloscope.
Loudness is a physiological sensation sensed by the brain. It is subjective but related to sound intensity.

7. Common Levels of Sound SOURCE OF SOUND LEVEL (dB)
Jet Engine, at 30 m 140
Threshold of pain
Loud rock music 115
Old subway train 100
Average factory 90
Busy street traffic 70
Normal speech 60
Library
Close Whisper 20
Normal breathing 10
Hearing threshold 0

8. Forced Vibration
The vibration of one object cause another object to vibrate.
Sounding boards are used to increase the volume (amplitude) of a vibrating object (like a string).
STRINGS
SOUNDING
BOARD

9. Natural Frequency
Everything vibrates, from planets and stars to atoms and almost everything in between.
A NATURAL FREQUENCY is one at which minimum energy is required to produce forced vibrations
also requires the least amount of energy to continue this vibration

10. Resonance
Resonance – when the frequency of a forced vibration on an object matches the object’s natural frequency, a dramatic increase in amplitude of the vibrations occurs.
For example, a swing, or the hollow box parts of musical instruments are designed to work best with resonance.
In order to resonate, an object must be elastic enough to return to its original position and have enough force applied to keep it moving (vibrating)

11. Interference
Sound waves interfere with each other in the same way as all waves.
Constructive interference - augmentation
Destructive interference - cancellation

12. The Doppler Effect: Waves from a Moving Source
Animation courtesy Dan Russell, Kettering University
v=f l so a smaller wavelength means a higher frequency. 12

13. The Doppler Effect
Motion of either the source or the observer of a wave causes the frequency to shift.
If the relative motion results in more wave crests reaching the observer per second, the frequency is increased.
If the relative motion results in fewer wave crests reaching the observer per second, the frequency is decreased. 13

14. The Doppler Effect 14

15. Levitation with sound waves
Paint
Pyro board
Water standing waves
Julius