1. Resonance

2. Quick Lab: Resonance Lengths of a Closed Air Column
MHR pg. 391
Answer the questions pg. 391#1-3

3. From the lab… Look at pg. 392 Figure 8.17
Notice the resonant length formula for a closed air column and open air column is the same as the length for an free/fixed medium ( previous class)

4. Recall: Media with fixed ends or free ends Ln = nλ/2 Where:
Ln = length of the medium or string
n= number of harmonics ie 1,2, 3 etc.
λ= wavelength
Media with fixed ends and free ends Ln = (2n-1)λ/4

5. Problem #1: Closed Air Column
A vibrating tuning fork is held near the mouth of a narrow plastic pipe partially submerged in water. The pipe is raised, and the first loud sound is heard when the air column is 9.0 cm long. The temperature in the room is 20 oC.
a) Calculate the wavelength of the sound produced by the tuning fork
b) Calculate the length of the air column for the second and third resonances.
c) Determine the frequency of the tuning fork.
Answers:
a) λ = 36 cm
b) L2 = 27 cm, L3= 45cm
c) f = Hz

6. Some practical applications: Mechanical Resonance
In a building, each component of the structure has its own natural resonant frequency and harmonic.
When an external force such as wind vibrates the building close to its natural resonant frequency, the building may start to sway.
Engineers are careful to build structures that will have components that will cancel out each other’s natural resonance.

7. Guess what I am…
Maximum sway in 190 km/h winds with 320 km/h gusts (120 mph winds with 200 mph gusts):
Antenna: 6 ft., 8 in. from centre
Sky Pod: 3 ft., 4 in. from centre
Tower Sphere: 1 ft., 7 in. from centre
Do you know what I am?????

8. You got it!!!!
DING DING DING
The CN Tower

9. Your Turn…
MHR pg. 396 #11-15
Finish handout on Standing Waves and Harmonics