Forced Vibration and Resonance

1. Forced Vibration and Resonance

2. Natural Frequencies Nearly all objects, when disturbed, will vibrate.

3. Natural Frequencies Objects tend to vibrate at their own particularfrequency

4. Natural Frequencies This frequency is known as the natural frequencyof the object.

5. The glass “harp” • http://www.huffingtonpost.co.uk/2013/02/15/hallelujah-wine-glasses-video_n_2693037.html • http://www.youtube.com/watch?v=S5K-43bjRwU

6. Resonance

7. Resonance Definition: when the frequency of a vibration on an object matches the object’s natural frequency…a dramatic increase in height occurs

8. Resonance An object that is forced at its natural frequency will resonate (vibrate) at that frequency (with increasing amplitude if the forcing continues). Consider the forced vibration of a child on a swing – pushing at the natural frequency increases the amplitude.

9. Resonance An object that is forced at its natural frequency will resonate (vibrate) at that frequency (with increasing amplitude if the forcing continues). http://www.youtube.com/watch?v=nHSGd2X1nc8&feature=related

10. Resonance An object that is forced at its natural frequency will resonate (vibrate) at that frequency (with increasing amplitude if the forcing continues). The Tacoma-Narrows Bridge: http://www.youtube.com/watch?v=xox9BVSu7Ok

11. Resonance • In 1831 soldiers were ordered to “break step” across bridges to avoid producing a frequency equal to the natural frequency of the bridge. • According to accounts of the time, the bridge broke apart beneath the soldiers, throwing dozens of men into the water.

12. Resonance: Example For example, the sound wave produced by a vibrating tuning fork will cause an identical tuning fork to start vibrating.

13. Examples of resonance • 1) breaking glass • 2) bridges • 3) walls (walls of Jericho) • 4) radio stations • 5) microwave ovens…water molecules in food vibrate and resonate and heat up