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Resonance

Resonance. Natural Frequency. All objects have a “ natural frequency ” at which they will oscillate if disturbed. Examples: Pendulum Child on a swing Wine glass Tuning fork Bouncing ball Human being?. Tuning Fork Example!.

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Resonance

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  1. Resonance

  2. Natural Frequency • All objects have a “natural frequency” at which they will oscillate if disturbed. • Examples: • Pendulum • Child on a swing • Wine glass • Tuning fork • Bouncing ball • Human being?

  3. Tuning Fork Example! • When objects are allowed to vibrate freely, they do so at their natural frequency

  4. Eventually, all vibrations will fade.

  5. How can you keep a vibration going?

  6. Forced Vibration • A forced vibrationis one in which the object is continually pushed/vibrated in phase with the natural vibration in order to maintain or grow its motion.

  7. Driving f versus Natural f • When the frequency of the forced vibration (driving frequency) matches the natural frequency of the object, the object experiences RESONANCE. • Most often this involves oscillations with ever growing amplitude.

  8. Wine Glass Demo

  9. Tacoma Narrows Bridge 1940 Tacoma Narrows Bridge – Washington State – wind matched the frequency of the bridge and caused it to be sent into a torsional vibration which destroyed the bridge http://www.youtube.com/watch?v=MBV-KA4ucSs http://www.youtube.com/watch?v=aZQlmxrmjXQ

  10. Human Resonance

  11. Radio Stations

  12. Resonance - The transfer of energy from one object to another having the same natural frequency Sympathetic Vibration – the response to a vibration with the same natural frequency http://www.youtube.com/watch?v=zWKiWaiM3Pw http://www.youtube.com/watch?v=JDnNmLkQ3Bc

  13. The Result of Resonance • When energy is transferred through resonance, the energy results in an increased amplitude of the vibration • If we play our music louder and louder, the windows in your room will vibrate with a greater amplitude until they can’t take it and they break

  14. Examples • Shimmy in your car at a certain speed • Windows rattle as a large truck passes by • Earthquakes/strong winds – match the natural frequency of buildings/bridges and makes them vibrate and can make them crumble – taken into account by architects

  15. http://www.youtube.com/watch?v=3FM4E19PZhw • http://www.youtube.com/watch?v=8Yx3nK7si-Q

  16. Wacky Resonance • In the world wars, soldiers used to march out of step over bridges so that it would not match the natural frequency of the bridge and make it crumble

  17. During a street party in London, England calls were made to police about an earthquake in outlying areas created by the synchronization of the dancers that match the natural frequency of different parts of the city

  18. Countering Resonance • We use dampers • A damper removes energy from a structure by absorbing it

  19. An opera singer can get a glass to vibrate when he/she matches the correct natural frequency – can break the glass • http://www.youtube.com/watch?v=17tqXgvCN0E

  20. Resonance in the Body: • entire body – 6 Hz • head – 13 – 20 Hz • eyes – 35 – 75 Hz • Large amplitude vibrations at any of these frequencies could irritate and/or damage parts of the body • efforts are made to reduce vibrations in construction i.e. bulldozer, jackhammer etc.

  21. Uses of Resonance • eggs exposed to ultrasound will resonate at a narrow range of frequencies – if there is salmonella in the egg is vibrates at a different frequency and can be detected and thrown away • same thing is used to detect the presence of biological and chemical warheads in a missile or artillery shell – don’t have to open it

  22. Homework  • Provide definitions for the following terms in your own words: frequency, amplitude, forced vibration/driving frequency, in phase, resonance and sympathetic vibration. • Explain how your friend pushing you on a swing relates to resonance. Use the terms frequency, amplitude, forced vibration/driving frequency, in phase, resonance and sympathetic vibration. • Explain how a wine glass can shatter due to a person’s voice. Use the terms frequency, amplitude, forced vibration/driving frequency, in phase, resonance and sympathetic vibration. • Your friend is over at your house and starts playing the new Drake album. You notice when he plays his favourite song, the windows start vibrating. He wants to play it again and crank up the volume. Why is this a bad idea? • Research dampers. What is their purpose? Draw a diagram of a vibration that is being dampened.

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