Transcript Foundations of Physics

Sound Notes
The Nature of Sound
 Sound travels in longitudinal waves consisting of oscillating compressions and
rarefactions through the air.
 Sound travels at 340 m/s in air at 20 C
Compressions
Rarefactions
The Nature of Sound
For each increase of 1°C above 0°C, speed of sound increases by 0.6 m/s.
The speed of sound also increases as the density of the medium increases.
in air = 340 m/s)
in warm air > 340 m/s
in water = 4 times faster than air
in steel = 15 times faster than air
Frequency and Pitch
•
Pitch - The highness or lowness of the sound
•
Depends on the frequency of the sound wave
Amplitude and Loudness
 Loudness – describes the intensity of the sound.
 Loudness is measured in decibels (dB)
 Depends on the amplitude of the sound wave (energy of the sound wave)
The Doppler Effect
 The shifting of the frequency (pitch) of a sound wave
due to the motion of the source of the sound or the
observer of the sound (or both).
Stationary Source
Moving Source
Lower
frequency
waves
Sound waves radiate out equally in all
directions
Higher
frequency
waves
Sound waves are pushed together in
the direction of motion and spread
farther apart as the source moves away
Resonance
Resonance occurs whenever successive oscillations are applied to a vibrating
object in rhythm with its natural frequency.
Acoustics
 The study of sound wave production and behavior
 Includes other fields including music , architecture,
engineering, medicine, oceanography, and zoology.
Human Hearing
 Research the internet to determine what frequencies
humans can hear. Compare these frequencies to at
least two other animals.
 Research the internet to determine the loudness scale
of human hearing. Explain how loud sounds can
actually damage your hearing and cause physical pain.
Human Hearing
 Humans can hear frequencies from 20 Hz to 20,000
Hz.
 Sounds louder than 130 dB can cause physical pain
because the ear receives so much energy the ear drum
and ossicles vibrate too much and can be permanently
damaged.
Human Hearing
 Loudness scale
Music and Musical Instruments
 Use the following link to discover how the four classes
of musical instruments produce different notes.
http://method-behind-the-music.com/mechanics/
Music and Musical Instruments
 Brass and woodwind instruments change the pitch of
the notes by changing the length of the vibrating air
column inside the instrument.
 The longer the vibrating air column, the longer the
wavelength of sound produced. Longer wavelength
sounds have lower frequencies resulting in a lower
pitch sound.
Music and Musical Instruments
 String instruments change the pitch of the notes by
changing the length of the vibrating string. Longer
vibrating strings produce sounds with longer
wavelengths.
 As the wavelength of the sound increases, the
frequency and pitch decreases.
 Acoustic instruments have hollow bodies to help
amplify the sound produced by the vibrating strings.
Music and Musical Instruments
 Percussion Instruments produce different pitch notes
by causing different lengths of materials to vibrate.
 Longer vibrating objects result in longer wavelength
sound waves and lower frequencies and pitches.
 Many percussion instruments have hollow spaces to
help amplify the sound produced by the vibrating
object.