Download Lesson 1 Notes

What is sound?
sound wave- a longitudinal wave created by vibration in a medium
 in a longitudinal wave the particles (molecules) of the medium
vibrate in the same direction that the energy travels (parallel)
 this movement cause particles to squeeze together in areas
called compressions and other parts that the particles are
spread out called rarefaction
How do sound waves travel?
 must travel through a medium even though only the
sound wave moves through in (the matter/particles/molecules do not
change position)
 a vacuum is a place with no matter at all (ex. outer space); sound cannot
travel in a vacuum
How do we hear sounds?
1. Sound waves travel from source to the ear drum
2. The ear drum transfers the vibrations to 3 tiny bones
in the middle ear (hammer, anvil, and stirrup). The bones
carry the vibrations through the oval window, the entrance
to the inner ear.
3. The vibrations passes through the oval window to the fluid
filled snail shaped cochlea. The cochlea turns the vibrations
into electric signals that it sends to the brain through the
auditory (sound) nerve.
What determines pitch?
 pitch- how high or low a sound is perceived
 frequency and wavelength
o freq. is given in hertz (Hz)
o 1 hertz = 1 wavelength (wave cycle)
per second
o
o
o
o
higher the freq. the shorter the wavelength
lower the freq. the longer the wavelength
high freq. = high pitch =short wavelength
low freq.= low pitch = long wavelength
What makes a sound loud?
 amplitude
o loudness- a measure of how well a sound can
be heard
o amp. is the maximum distance the particles in
a wave’s medium vibrate from their rest
position
o if you hit a drum harder you increase the
amp. of the wave
o higher amp.= loud sound
o low amp. = quiet sound
How is loudness measured?
 characteristic of a wave that describes intensity
 measured in decibels(1/10 of a bel, the base unit)

How loud is too loud?
 loud sounds (painful or not) can
damage your hearing
 loud sounds damage the small
hairs on the cochlea that carry
electric signals to the nerve
and do not repair themselves
What is the Doppler effect?
 Doppler effect- the change in
pitch (observed frequency) when
the sound source or the observer
are moving
 if moving closer together, the
sound waves are closer together
(higher frequency) and sounds
higher pitched
 if moving further apart, the
sound waves are farther apart
(lower frequency) and sounds
lower pitched