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Sound

Sound. Sound Waves. Sound waves travel as compression waves. Another name for compression waves is longitudinal waves. Factors affecting speed of sound. Temperature – Sound moves through hot air faster than cold air due to the increased speed of the particles.

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Sound

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  1. Sound

  2. Sound Waves • Sound waves travel as compression waves. • Another name for compression waves is longitudinal waves

  3. Factors affecting speed of sound • Temperature – Sound moves through hot air faster than cold air due to the increased speed of the particles. • Type of medium – Sound moves well through dense material and material that returns quickly to its original position.

  4. Factors affecting speed of sound • Thus, sound moves fastest in a solid and slowest in a gas • Sound travels more quickly through solids and liquids because the individual molecules are closer together than the molecules in gas • Sound waves CANNOT move through a vacuum – they need a medium!

  5. Bells in a bell jar…

  6. Decibels • The decibel (dB) is the unit used to measure sound intensity or loudness. • Loudness corresponds to the amplitude of a wave.

  7. Decibels • Sounds greater than 120 dB can cause pain in human ears. • Sounds with an amplitude between 0 dB and 120 dB are called audible. • Anything below 0 dB is considered subaudible.

  8. Decibel drag races

  9. Frequency and Pitch • Pitch – how high or low a sound is. • High pitch = high frequency • Low pitch = low frequency

  10. Frequency and Pitch • Humans can hear pitches that have a frequency between 20 Hz and 20,000 Hz • Pitches above 20,000 Hz are called ultrasonic. • Pitches below 20 Hz are called subsonic.

  11. Phone Tone Generators

  12. Doppler Effect • The Doppler effect is a change in the frequency or pitch of a sound that is caused by either the movement of the source or the observer of the wave. • Example: The sound from an ambulance siren changes as it approaches the listener

  13. Doppler Effect • First observed in 1842 by Christian Andreas Doppler The Big Bang Theory - Doppler Costume Video explaining the Physics of the Doppler Effect

  14. Resonance • Resonance is the vibration of an object at its natural frequency. • Example: Windows rattle when the sound from a passing truck matches the window’s natural resonance.

  15. Resonance of different things

  16. Nodes and Anti-nodes • Node – A place where two waves meet and destructively interfere so that the displacement is zero

  17. Nodes and Anti-nodes • Anti-node – the point of largest amplitude when two waves interfere constructively

  18. Music – Natural Frequency • A natural frequency exists without any driving source. • It is a natural frequency if its waveform has nodes that match up with the ends of the object. • The lowest frequency at which this occurs is the fundamental, or the 1st Harmonic.

  19. Music - Harmonics • Harmonics – a sound wave with a pitch that is a multiple of the natural frequency • Overtone – has a higher frequency than the fundamental • Octave = ½ or double the frequency of a sound; 8 notes on the musical scale

  20. Music • Consonance – multiple waves combining to form a pleasant sound • Dissonance – multiple waves combining to form an unpleasant sound • Acoustics – the control of noise and the vibrations that cause noise

  21. Toccata Fugue in D Minor

  22. Music – open pipe resonators • Open pipe resonators – both ends are open • Examples: brass instruments, flutes, saxophones • It reflects an inverted wave

  23. Music - Closed pipe resonators • Closed pipe resonators – have one end enclosed • Example: pan-flute, blowing across a bottle top, hanging pipes under marimbas, xylophones

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