Wednesday, February 4, 2009

5th Lecture, Wave intereference, standing waves, resonance, sound

I felt like today was a really good lecture. Almost every time I looked at students' faces for feedback, I saw most of the class interested and focused. I felt like it was a class session that "clicked" and I believe that's true. I wish I knew the magic ingredient! Actually, I don't think there was a magic ingredient. I don't have any scientific evidence, but my feeling is that were a few key ingredients to making today's class effective:
  • Fascinating physics. Waves are fascinating. Wave interference is even more fascinating. On top of it being fascinating, I think the topics were new to most students.
  • Solid demos and applets. The core demos today were the wave table (fantastic) and the flame tube (not as fundamentally solid as the wave table, but gets a tremendous boost from using fire). The core applet was again the Falstad ripple tank, which we used for study of wave interference. I've already mentioned how awesome that applet is. But I should mention it again. That applet is awesome.
  • Solid youtube videos. We looked at some resonance things, culminating in the famous Tacoma narrows bridge collapse.
  • I was having fun and I think I provided good context and connection of all these things. Besides their facial expressions, I also got direct feedback after class from a few students saying they enjoyed the class. I could be wrong, of course, but I really feel like people learned.
So, below, I've embedded the slideshare slides from today. I don't want to go over ever slide, but I'll point out a couple things that seemed to work well (besides the general things above).

  • I think the students enjoyed looking at the "student answers" to the homework question. I've been doing this for a couple years, and I think it's related to "just in time teaching (JiTT)" that I learned about at the new faculty workshop. It's actually quite time consuming to do this, though, and even after about 3 hours that I put into reading through their answers, I didn't feel like I was completely fair in picking the "best" answers. But I explained this to the students, and I think they are fine with that. Also, by the way, I thnk that while 3 hours is a bunch of time to spend on something like that, I do feel it's worth the investment.
  • I think that demonstrating wave interference with the wavetable was very effective. I asked for a student volunteer, and Ashley was quick to jump up and help. We were easily able to synchronize two counter-propagating traveling waves on the wave table. When the waves met in the middle, the amplitude clearly visually increased. Furthermore, the constructive interference was large enough amplitude for the rods to hit the table and make a "ding" sound. I love the "ding" sound, because I feel like it announces to the whole room that the waves interfered to produce a bigger wave. Thanks, Ashley, for your help with this demo!
  • The video of someone creating standing waves with the wavetable was effective. I'm not talented enough to do this live in front of the class, so the video is very helpful. I think you can find the videos here.
OK, that's my update for today. I'm very happy that I think it was an effective class, and I'm also very happy for another reason that I can hopefully blog about in about 30 days!


  1. Just wanted to say thanks so much for the JITT link -- great stuff -- thinking about ways of using it in my own classes, but also in the some of the teacher training I do -- even if they don't use it electronically, the concept itself is advanced teaching and could be implemented in non-networking environments (with some good teacher control!)

  2. You're welcome. I've been noticing a few (say 3%) of the students thriving on non-text JiTT assignments. For example today I gave them an alternate assignment of taking photographs using their diffraction gratings. Three students turned in really great photographs of spectra of the sun and fluorescent lights. This was out of about 50 that turned in an answer at all, and 150 in the entire class. Their grade is not at all affected by whether they do the assignment at all. 3% isn't a big hit rate, but on the other hand, I think those 3 students really learned a lot.


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