1.  Please take out: Sound Station Lab Natural frequency and resonance notes

2. #1 What happens to the frequency every time a new harmonic is achieved? ○ The frequency increases by about the same amount each time.

3. #2  Looking at the data below, at about what frequency should you find the 8 th harmonic? About 120.8 Hz Harmonic Frequency (Hz) Wavelength (cm) Wave Speed (cm/s) 345.333.41513 460.625.01515 575.920.01518 691.216.61514

4. #3 4 waves

5. #4  v = f λ v - speed f - frequency λ - wavelength

6. #5  How can the wave speed remain constant even though the frequency increases? The increase in frequency is exactly balanced by the decrease in the wavelength.

7. #6  Natural Frequency – The frequency that an object oscillates at

8. #7  When you get close to the natural frequency, the amplitude of the string’s vibration suddenly increases and a standing wave is formed.

9. #8  When wind blows over or past a building or bridge, the wind will cause the structure to oscillate. In the case of the Tacoma Narrows bridge outside Tacoma, WA, the bridge’s natural resonance match the resonance of the wind. Watch the Video It is important to make sure the natural resonance of buildings and bridges doesn’t match any vibrations in the environment.

10. #8  Resonance occurs when the frequency of the force that is causing the oscillations exactly matches the natural frequency of the object.

11. #9  Examples of resonance Tacoma Narrows Bridge Person on swing Breaking a glass with sound

12. #10  Standing Wave – a wave that is trapped in one spot. #11  Nodes – points where the string does not move #12  Anti-nodes – points where the motion of the string is at a maximum

13. #13  1 st Harmonic – is the lowest natural frequency of the string. #14  The string will achieve resonance anytime it is vibrated with a multiple of the first harmonic

14. #16  Interference – the interaction of two or more waves #17  Constructive Interference – when two waves overlap crest to crest. The amplitude of each wave combines to make a large wave

15. #18  Destructive Interference – when two waves overlap crest to trough The positive amplitude of the crest cancels with the negative amplitude of the trough The wave appears to die

16. Noise Canceling Headphones  Use destructive interference to reduce the amount of noise that you hear. Super fast computer detects outside noise and creates a sound wave that destructively interferes with the noise The two waves cancel each other out Noise from the airplane Sound Created by Headphones

18. Only the energy travels, air molecules vibrate in place

19. Sound is a longitudinal wave