1. Bell Ringer – Fri, 12/5 1.Describe constructive interference in your own words. How is it different from destructive interference? 2.What does it mean when two waves are “out of phase?” 3.Are the two waves below in phase or out of phase? LT: We will explain how constructive interference produces resonance.

2. Learning Target We will explain how constructive interference produces resonance.

3. When waves cross paths 1.Constructive Interference: when two waves are “in phase,” they add to each other.

4. When waves cross paths Destructive Interference: when two waves are “out of phase,” they subtract from each other.

5. Resonance Resonance: repeated constructive interference results in massive wave amplitude increase Only happens on certain frequencies

6. Interference in action: Resonance Another effect of constructive interference is called RESONANCE If two objects have the same frequency, then sending a tone at that frequency causes the amplitude of the waves to keep constructively interfering

7. Interference in action: Resonance Resonance example 1: Sound wave opera singer Resonance example 2: Tacoma Narrows Bridge https://www.youtube.com/watch?v=17tqXgvC N0E https://www.youtube.com/watch?v=xox9BVSu 7Ok “Professor F. B. Farquharson continued wind tunnel tests. He concluded that the ‘cumulative effected of undampened rhythmic forces’ had produced ‘intense resonant oscillation.’”

8. Resonance Lab Frequency (Hz)Shortest Resonance (m) Wavelength (m)Speed (m/s) 4000 5120.130.52266 4800.140.56268 Copy this data table into your notebooks.

9. Resonance Lab Procedure 1.Fill your graduated cylinder ¾ of the way with water. Insert PVC pipe. 2.Strike your tuning fork on something soft (the heel of your hand or knee). Hold it over the top of the pipe. 3.Listen for the pipe to amplify it. Mark the point where the PVC touches the water with one of your rubber bands.

10. Resonance Lab Procedure 4.Find the next resonant frequency. 5.Record your data. Only fill out the second column at this time. 6.Repeat with new tuning fork.

11. Resonance Lab Analysis To calculate wavelength, multiply shortest resonance by 4. To find speed, multiply frequency by wavelength!

12. Resonance Lab Analysis Frequency (Hz)Shortest Resonance (m) Wavelength (m)Speed (m/s)

13. Speed of what?!?!? Speed of sound in air: 333 m/s How close were we? Supersonic flights: https://www.youtube.com/watch?v=gWGLAAYdbbc

14. Several positions along the medium are labeled with a letter. Categorize each labeled position along the medium as being a position where either constructive or destructive interference occurs.

15. Extra Practice Handout

16. Exit slip