1. PHYS16 – Lecture 39 Ch. 17 Sound “Since light travels faster than sound, is that why some people appear bright until you hear them speak?”

2. Up Participation Grade Measure the period and length of the 4 story pendulum in the stairwell… – Calculate “g” – Put in lab notebook – Email me & earn 4 points http://www.problogger.net/wp-content/uploads/2007/10/google-pendulum.jpg

3. Energy and Power Energy is conserved when a wave reaches a medium change Power =Energy per time

4. Standing Waves Standing waves – waves that constructively interfere in a cavity and “stand” in one spot http://kottan-labs.bgsu.edu/teaching/workshop2001/chapter7_files/image023.gif Node Antinode

5. Demo: Standing Waves on String What happens to standing waves: – as I increase driving frequency? – as I increase the tension? – If I were to increase cavity length? http://d3.ac-videos.myspacecdn.com/videos02/102/thumb1_38a56a2f95314e179cd4dfef580b1bb6.jpg

6. Demo: Guitar

7. Waves post-question PhET website

8. Waves post-question PhET website 0.0133

9. Waves post-question Which of the waveforms has the shortest period? A) 1 st harmonic B) 2 nd harmonic C) 3 rd harmonic D) Superposition of 1 st, 2 nd, & 3 rd harmonic E) Not enough information

10. Waves post-question A string of 0.25 kg/m is stretched to a tension of 4 N between 2 plates that are 0.5 m apart. What is the wavelength of the first harmonic in the string? A)4 m B)2 m C)1 m D)0.5 m E)0.25 m

11. Main Points - Waves Wave speed – If the string/medium doesn’t change then speed stays constant at: – If the cavity length doesn’t change then the wavelength for a particular harmonic is constant – If the pulse driver stays constant (me wiggling wrench) then frequency is constant