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

2. #1 The frequency increases by about the same amount each time.
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 8th harmonic?
About Hz
Harmonic
Frequency (Hz)
Wavelength (cm)
Wave Speed (cm/s) 3
45.3
33.4
1513 4
60.6
25.0
1515 5
75.9
20.0
1518 6
91.2
16.6
1514

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

10. #9 Examples of resonance Tacoma Narrows Bridge Person on swing
Breaking a glass with sound

11. #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

12. #13
1st Harmonic – is the lowest natural frequency of the string (fundamental).
#14
The string will achieve resonance anytime it is vibrated with a multiple of the first harmonic

13. NEW INFORMATION!
#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

14. #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

15. 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

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

18. Sound is a longitudinal wave

19. Labeling a Longitudinal Wave