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VIBRATION!

VIBRATION!. Physics Unit 12. Natural Frequency, w n. All objects have a frequency at which they will sustain vibrations with the minimum energy input A 256 Hz tuning fork always vibrates at 256 Hz when struck. This “natural frequency” depends on properties of the object that’s vibrating

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VIBRATION!

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  1. VIBRATION! Physics Unit 12

  2. Natural Frequency, wn • All objects have a frequency at which they will sustain vibrations with the minimum energy input • A 256 Hz tuning fork always vibrates at 256 Hz when struck. • This “natural frequency” depends on properties of the object that’s vibrating • Size • Shape • material

  3. Tuning forks of different frequencies have different lengths. • Which of these do you think will have the highest wn and why? • Hint: think about inertia

  4. Forced Vibration • Occurs when the vibration in one object causes a nearby object to vibrate at the same frequency • Examples • Car radio makes the windows rattle • “feeling” loud sounds through walls or the floor

  5. Resonance • Happens when an object is forced to vibrate at its natural frequency • Standing waves are created as waves interfere with themselves • Amplitude increases dramatically due to constructive interference • Objects in resonance can literally tear themselves apart! • Opera singer shatters a glass with her voice • Doctor uses ultrasound to break up a patient’s kidney stone

  6. More on resonance • Since objects have only one natural frequency, they will only resonate at one frequency. • If singing an “A” (440 Hz) shatters a wine glass, singing a “C” (256 Hz) will not • Since an object’s shape, size, and material affect wn, these factors also affect the point at which they will resonate.

  7. Tacoma Narrows Bridge Disaster • Keep these wave concepts in mind as you watch the video of the bridge collapse in Washington state.

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