201241723 mz mandhlazi

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201241723 mz mandhlazi

  1. 1. How can I explain the concept of SOUND, WAVES AND DOPPLER EFFECT?
  2. 2. WAVES are everywhere. We encounter them on a daily basis. Examples of waves are:     
  3. 3. WAVE - a disturbance traveling through a medium or in a vacuum from one location to another.
  4. 4. is the maximum distance the particles in a wave vibrate from their rest positions. - the number of waves produced in a given time
  5. 5. Frequency= waves/time
  6. 6. SOUND It is composed of waves of compression and rarefaction in which the human ear is sensitive
  7. 7. Sound may be described by four perceptual characteristics:  Pitch – refers to the highness or lowness of a sound. It depends upon the frequency of the sounding object. Higher frequency sounds produce high pitch while lower frequency sounds produce low pitch.  Loudness – is a physiological sensation that varies from one person to another. It depends on the sense of hearing, the distance from the source and the material through which the sound travels.
  8. 8. Pitch -description of how high or low the sound seems to a person . Loudness- how loud or soft a sound is perceived to be.
  9. 9. Sound Waves – is a longitudinal wave created by vibrating solids, liquids or gases and capable of producing a sensation in our auditory system. It can travel through a medium from one location to another. It travels at a speed of 331m/s in air at sea level when the temperature is 0 degree.
  10. 10. This music is so loud please turn it UP…
  11. 11. Loudness of Sound in Decibels
  12. 12. Just like all longitudinal (compression)waves,sound Wavespossess a velocity, frequency,wavelength, phase,period, and amplitude. Sound waves also reflect, refract, diffract, and interfere.
  13. 13. 2. LOUDNESS or intensity -description of how high or low the sound seems to a person -determined mainly by the amplitude of the sound wave a. Decibel (dB)- unit used to measure sound intensity or loudness.
  14. 14. Speed of Sound Depends on: 1. Type of medium -travels better through liquids and solids and gas can’t travel through a vacuum. 2. Temperature of medium -travels faster at higher temperature. 3. Density -sound moves well through dense materials. 4. Elasticity -sound waves move fast through elastic materials
  15. 15. Human Hearing sound wave vibrates ear drum amplified by bones converted to nerve impulses in cochlea
  16. 16. Ultrasound - sound waves with frequencies above the normal human range of hearing. Sounds in the range from 20-100kHz Infrasound - sounds with frequencies below the normal human range of hearing. Sounds in the 20-200 Hz range
  17. 17. DOPPLER EFFECT
  18. 18.  The apparent change in the frequency of a source of wave due to the motion of the source and/or the observer  Developed by Christian Doppler in 1842  The difference of the true frequency and the apparent frequency is called the Doppler Shift
  19. 19. Doppler Effect The Doppler effect is the apparent change in the frequency of sound due to the motion of source of sound and/or the observer.
  20. 20. The following symbols will be used in the definitions:  fis the true frequency  f’ is the apparent frequency  v is the velocity of the sound (air)  vs is the velocity of the source  vo is the velocity of the observer  λ is the true wavelength  λ’ is the apparent wavelength Key variables
  21. 21. Case 1:observer is in motion and the source is at rest  f ’ = [ ( v ± vo ) / v ] f  ( + ) means the observer is moving towards the source  ( - ) means the observer is moving away from the source
  22. 22. Case 2:observer is at rest and the source is in motion  f ’ = [ v / ( v ± vs ) ] f  ( + ) means the source is moving away from the observer  ( - ) means the source is moving towards the observer
  23. 23. Case 3:both the observer and the source are in motion  f ’ = [ ( v ± vo ) / ( v ± vs ) ] f  NOTE: please refer to case 1 and case 2 and analyze the situation of the observer and the source respectively.
  24. 24. Conceptual understanding  When a wave source moves toward a receiver, does the receiver encounter an increase in wave frequency, wave speed ,or both?  Does the Doppler Effect occur for only some types of waves or all types of waves?
  25. 25.  Doppler Effect  change in wave frequency caused by a moving wave source moving toward you - pitch sounds higher moving away from you - pitch sounds lower
  26. 26.  named after Austrian physicist and philosopher Ernst Mach  Used to describe speed of objects that are travelling close to, or above the speed of sound.  The ratio of the speed of the object and the speed of sound in the medium.  M = speed of object / speed of sound
  27. 27. Shock waves  this is heard as a sonic boom when an airplane passes over; this is the result of the compilation of sound waves generated by a source that moves at equal or greater velocity than the sound it creates
  28. 28. Sample problems: Doppler effect 1. An ambulance traveling at 20. m/s sounds its siren at a frequency of 256Hz. What apparent frequency will you hear if the ambulance is: ( assume air temperature to be at 25°C ) a. approaching you? b. moving away from you? 2. A car traveling at 30. m/s sounds its horn as it overtakes and pass another car traveling at 20. m/s in the same direction. If the frequency of the horn is 500. Hz, what is the frequency heard by the driver in the slower car: a.) before b.) after the car has passed? Assume sound speed to be at 350. m/s.
  29. 29. LIST OF REFFERENCES  This presentation is the combination of sources by the following:  Agatonlydelle. (2012). Physics Sounds. Online: http://www.slideshare.net/agatonlydelle/physics-sounds. Accessed online on: 06 march 2014  HMLSS21. (2012). Sound Waves BSU-ARASOF. http://www.slideshare.net/HMLSS21/sound-waves-bsuarasof. Accessed online on: 05 march 2014  Marium S. (2013). DAV Lecture: WAVE INTERACTIONS. Online: http://www.slideshare.net/saramarium1/sound-and-waves-26412647. Accessed online on: 05 march 2014  Moral F. (2014). Teacher at B.R.I.G.H.T. Academy: The Doppler effects. Online: http://www.slideshare.net/teacherfidel/16-the-doppler-effect?qid=c0a01b02- 9c80-4a3c-861c-c18f4e6146e9&v=qf1&b=&from_search=2. Access online on: 05 march 2014

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