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Resonance

Resonance. IDS Physics: Unit 5. Natural Frequency. All oscillators have a natural frequency. If disturbed from equilibrium, this is the frequency at which they will oscillate. example: mass on a spring. Forced Vibrations.

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Resonance

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  1. Resonance IDS Physics: Unit 5

  2. Natural Frequency • All oscillators have a natural frequency. • If disturbed from equilibrium, this is the frequency at which they will oscillate. • example: mass on a spring

  3. Forced Vibrations • A tuning fork is not very efficient at transferring it’s energy to the air. • A table can be forced to vibrate at the frequency of the tuning fork and thus better transfer the sound energy to the air.

  4. Forced Vibrations • Sounding boards are examples of forced vibrations. • All string instruments use a sounding board that is forced to vibrate

  5. An experiment • Can Mr. B knock the mass off the spring with a piece of paper? • Yes – just add energy at exactly the right times and the oscillations will get bigger and bigger

  6. Resonance • Resonance occurs when a system is forced to vibrate at a frequency that is the same as the natural frequency of the system.

  7. Resonance • A swing (pendulum) is an example of resonance • It has a natural frequency • It is forced to vibrate at the same frequency as the natural frequency.

  8. Resonance

  9. Resonance Examples • One tuning fork can cause another to vibrate. • Parts of a car rattle at specific speeds. • English Troops cause a footbridge to collapse in 1831

  10. Resonance Examples • A singer’s voice can break a wine glass • Link: http://www.blazelabs.com/.%5Cpics%5Cglass.mov • Earthquakes cause buildings and structures to collapse

  11. Reflection of Waves • When a traveling wave encounters a barrier, it can be reflected. • The reflected wave will have the same amplitude and frequency as the original wave.

  12. Standing Waves • When an incoming and reflected wave meet, interference occurs • At some places, this interference will be destructive • These places where the medium does not move are called nodes

  13. Standing Waves • At some places, this interference will be constructive • These places where the medium has a maximum amplitude are called anti-nodes

  14. Standing Waves • A string instrument produces a standing wave when it is plucked or bowed.

  15. Standing Waves • The length of the string will be equal to ½ of a wavelength

  16. Standing Waves • The length of the string can be equal to a wavelength

  17. Standing Waves • The length of the string can be equal to 3/2 of a wavelength

  18. Standing Waves • For a string that is fixed on both ends, the length of the string must be equal to an integer number of half-wavelengths.

  19. Standing Waves • What about a column of air? (Like blowing over a coke bottle)

  20. Standing Waves

  21. Standing Waves

  22. Standing Waves • For a medium that is fixed on one end, (like a column of air in a bottle) the length of the string must be equal to an odd number of quarter-wavelengths.

  23. Making Music • Most instruments involve either strings or columns of air. • The speed of sound never changes, so you have to change the wavelength to change the pitch (frequency)

  24. Music

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