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201241723 mz mandhlazi


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  • 1. How can I explain the concept of SOUND, WAVES AND DOPPLER EFFECT?
  • 2. WAVES are everywhere. We encounter them on a daily basis. Examples of waves are:     
  • 3. WAVE - a disturbance traveling through a medium or in a vacuum from one location to another.
  • 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. Frequency= waves/time
  • 6. SOUND It is composed of waves of compression and rarefaction in which the human ear is sensitive
  • 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. 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. 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. This music is so loud please turn it UP…
  • 11. Loudness of Sound in Decibels
  • 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. 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. 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. Human Hearing sound wave vibrates ear drum amplified by bones converted to nerve impulses in cochlea
  • 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
  • 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. 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. 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. 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. 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. 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. 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.  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.  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. 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. 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. LIST OF REFFERENCES  This presentation is the combination of sources by the following:  Agatonlydelle. (2012). Physics Sounds. Online: Accessed online on: 06 march 2014  HMLSS21. (2012). Sound Waves BSU-ARASOF. Accessed online on: 05 march 2014  Marium S. (2013). DAV Lecture: WAVE INTERACTIONS. Online: Accessed online on: 05 march 2014  Moral F. (2014). Teacher at B.R.I.G.H.T. Academy: The Doppler effects. Online: 9c80-4a3c-861c-c18f4e6146e9&v=qf1&b=&from_search=2. Access online on: 05 march 2014