Waves and Sound
Chapter 15
Pages 470-495
© Waves are rhythmic disturbances that carry energy through matter or space
©
Waves generally travel through a medium
© A medium is a material through which waves can transfer energy
© Examples:
© Tidal waves transfer energy through water
© Earthquakes transfer energy through Earth
© Sound waves need a medium to carry them
© Transverse waves (ex: light)
© medium moves at right angles to the wave
© Ex: if wave moves from left to right, then the medium moves up and down
©
Longitudinal waves (ex: sound)
© medium moves in the same direction as the wave
© Ex: if waves moves from left to right, then the medium also moves left and right
See Transverse and Longitudinal Waves in action.
© Transverse waves have
© Crests – high part of the wave
© Troughs – low part of the wave
© Wavelength – distance from the top of one crest to the top of the next crest
© Amplitude – distance from the rest position to the top of a crest (or to the bottom of a trough)
--a-- ---------c----------
|||||||||| | | | | | | | | | | |||||||||| | | | | | | | | | | |||||||||| | | | | | | | | | |
------b-------
© Longitudinal (compressional) Waves have
©
A. Compression
– crowded area
(more dense)
©
B. Rarefaction
– uncrowded area
(less dense)
© C. Wavelength – one full compression plus one full rarefaction
© Frequency – is the # of waves that pass by each second
© It tells how “frequently” the waves pass by
©
Frequency is measured in waves per second
©
Hertz or Hz means waves per
second
© Pitch – highness or lowness of a sound
© (for a longitudinal wave)
© Pitch depends on frequency
© High frequency àhigh pitch
© Low frequency à low pitch
© Healthy human ear can hear sound frequencies ranging 20 Hz to 20,000 Hz
© Ultrasonic – “above hearing”
© sound with frequency above 20,000 Hz
©
Used in sonar and medical diagnosis
© Infrasonic – “below hearing”
© Sound with frequency below 20 Hz
© Produced by heavy machinery and thunder
© Intensity – relates to the amount of energy in the wave
© Intensity is related to amplitude
© Loudness – human perception of intensity
© Louder à more intensity àmore amplitude
© Measured in decibels (dB)
© 0 dB – quietest sound humans can hear
© 75 dB – vacuum cleaner
© 120 dB – may damage human ear
© 150 dB – jet plane taking off
© As an object moves toward you, the pitch seems to increase
© As an object moves away from you, the pitch seems to decrease
© Wavelength and frequency are related through the velocity (speed) of the wave
© v = λ x f or v = λ f
© v = velocity (speed)
© λ = wavelength (Greek letter L - lambda)
© f = frequency