2. Waves and Sound Chapter 15 Pages 470-495

3. What are waves? 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

4. What are the two main types of waves? 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.

5. What are Transverse Waves? Transverse waves have Crests – high part of the wave Troughs – low part of the wave

6. What are Transverse Waves? Transverse waves have 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)

7. What are longitudinal waves? A. Compression – crowded area (more dense) B. Rarefaction – uncrowded area (less dense) C. Wavelength – one full compression plus one full rarefaction --a-- ---------c---------- |||||||||| | | | | | | | | | | |||||||||| | | | | | | | | | | |||||||||| | | | | | | | | | | ------b-------

8. What is frequency? 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 Both waves shown have a frequency of 3Hz if each diagram takes place in 1 sec --a-- ---------c---------- |||||||||| | | | | | | | | | | |||||||||| | | | | | | | | | | |||||||||| | | | | | | | | | | ------b-------

9. What is pitch? Pitch – highness or lowness of a sound (for a longitudinal wave) Pitch depends on frequency High frequency  high pitch Low frequency  low pitch

10. What can we hear? 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

11. What can we hear? Intensity – relates to the amount of energy in the wave Intensity is related to amplitude Loudness – human perception of intensity Louder  more intensity  more 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

12. What’s the Doppler Effect? As an object moves toward you, the pitch seems to increase As an object moves away from you, the pitch seems to decrease Higher frequencyLower frequency

13. How are wavelength and frequency related? 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