# Days 136 & 137: In France, It Works?

Tuesday, May 8, and Wednesday, May 9

The end of the year is starting to get away from me. It keeps suddenly being tomorrow before I’m done with today.

Physics: Tuesday we started the very last chapter in the book, Chapter 40, about fusion and fission. The chapter starts with fission, so I answered their questions about the reading they did. Wednesday we watched a documentary from 1987 about the nuclear program in France called “In France, It Works”. It being thirty years old, I have no idea how relevant or correct it still is for today, but it was interesting.

Honors Physics: Tuesday is our double block, so I had them play with four different spring things (one super long slinky, one super tiny slinky, a phone cord, and a very long and tightly wound spring snake thing) take measurements related to wave speed and wave lengths, and do a compare/contrast of the different media. Mainly I wanted them to get a feeling for how waves move down a string and how different it is for a long snake spring vs a dang plastic phone cord.

Wednesday we finished up with Doppler Effect using some practice problems. My student who always asks me questions I don’t know the answer to asked another fantastic one. Why are the equations for a moving source and a moving observer different? Isn’t motion relative? Shouldn’t it be the same for both moving? I had never thought of that and didn’t have a good answer, so I told him I would look into it. I also found a video that did the mathematical derivation of the equations, and that made perfect logical sense, but still doesn’t explain the conceptual situation. He came up to me after class and said he was thinking about the difference at the extreme where the relative velocity is the speed of sound.

For a source moving at the speed of sound, the effective frequency in front of it is not there because all waves are emitted right on top of one another. Instead of hearing a sound at a frequency, you get a sonic boom. For an observer moving toward a stationary source at the speed of sound, there would still be spacing between the waves, so the heard frequency would be very high, but still exist. I definitely see how those situations are different, but I am having trouble organizing that for the difference between two cars, one blowing its horn, and one staying still while the other moves. Why is it different if motion is relative? Gonna have to think about this a lot more.

AP Physics: Mechanics FRQs and E&M MC.