1. Chapter 5 Wave Motions and Sound

2. Vibrations Repetitive, back-and-forth motion –Periodic or oscillation Cycle –one complete vibration Period –time for one cycle Frequency –number of cycles per second (units = hertz, Hz) Period and frequency inversely related. Repetitive, back-and-forth motion –Periodic or oscillation Cycle –one complete vibration Period –time for one cycle Frequency –number of cycles per second (units = hertz, Hz) Period and frequency inversely related. Fig 5.4 (Simple Harmonic Motion)

3. Waves Disturbance that moves thru a medium Causes –Periodic motionPeriodic motion –PulsePulse Two major considerations about a wave? –Traveling Disturbance –Transports Energy Mechanical waves –Require medium for propagation –Waves move through medium –Medium remains in place. Disturbance that moves thru a medium Causes –Periodic motionPeriodic motion –PulsePulse Two major considerations about a wave? –Traveling Disturbance –Transports Energy Mechanical waves –Require medium for propagation –Waves move through medium –Medium remains in place.

4. Kinds of Waves Longitudinal waves Vibration direction parallel to wave propagation direction Particles in medium move closer together/farther apart –Example: sound waves Gases and liquids –Support only longitudinal waves. Longitudinal waves Vibration direction parallel to wave propagation direction Particles in medium move closer together/farther apart –Example: sound waves Gases and liquids –Support only longitudinal waves.

5. Kinds of Waves (cont’d) Transverse waves Vibration direction perpendicular to wave propagation direction –Example: plucked string Solids –Support both longitudinal and transverse waves. Transverse waves Vibration direction perpendicular to wave propagation direction –Example: plucked string Solids –Support both longitudinal and transverse waves.

6. Waves in Air Longitudinal waves only Large scale - swinging door creates macroscopic currents Small scale - tuning fork creates sound waves Series of: –Condensations (overpressures) and –Rarefactions (underpressures). Longitudinal waves only Large scale - swinging door creates macroscopic currents Small scale - tuning fork creates sound waves Series of: –Condensations (overpressures) and –Rarefactions (underpressures).

7. Describing Waves Graphical representation Pure harmonic waves = sines or cosines Wave terminology Wave propagation speed. Graphical representation Pure harmonic waves = sines or cosines Wave terminology Wave propagation speed.

8. Sound Waves Require medium for transmission Speed varies with –Inertia of molecules –Interaction strength Various speeds of sound. Require medium for transmission Speed varies with –Inertia of molecules –Interaction strength Various speeds of sound.

9. Velocity of Sound in Air Varies with temperature Greater kinetic energy thus sound impulse transmitted faster Increase factor (units!): 0.6 m/s per °C 2.0 ft/s per °C.

10. Eq 4.2 HW BONUS Question If the air temperature is 86ºF during a thunderstorm and the thunder took 2.3 seconds after the lightning was seen. How far away was the lightning strike? Determine the answer in feet and then convert to miles. How far away was the lightning strike? Determine the answer in feet and then convert to miles. HW BONUS Question If the air temperature is 86ºF during a thunderstorm and the thunder took 2.3 seconds after the lightning was seen. How far away was the lightning strike? Determine the answer in feet and then convert to miles. How far away was the lightning strike? Determine the answer in feet and then convert to miles. Then what?

11. “Visualization” of Sound Waves Boundary effects –Refraction –Reflection –Absorption. Boundary effects –Refraction –Reflection –Absorption.

12. Refraction Bending of wave fronts upon encountering a boundary.

13. Reflection Wave rebounding off boundary surface.

14. Absorption Wave energy dissipated.

15. Sounds from Moving Sources Doppler effect –Wave pattern changed by motion of source or observer –Moving Towards - shifted to higher frequency (blue) –Moving Away - shifted to lower frequency (red). Doppler effect –Wave pattern changed by motion of source or observer –Moving Towards - shifted to higher frequency (blue) –Moving Away - shifted to lower frequency (red). Doppler Homepage

16. Sounds from Moving Sources Supersonic speed –Shock wave and sonic boom produced. Supersonic speed –Shock wave and sonic boom produced. http://www.wilk4.com/misc/soundbreak.htm Bell X-1

17. Next Time: Quiz 2 (Ch 4 and 5) then Electricity