Lerner Physics

We finished standing waves today, for the most part. I had students gone to a concert, and I knew some of the pictures would be difficult to draw, so we did a lot of working in groups today. We also explained the results to our sound lab, and our results came out pretty darn close to what we expected.

When I went around the room today, trying to get a sense of where we were as a class, some students really liked this unit. Students told me that they liked how it applied to music, liked how it seemed to make sense, and liked that they could be successful with it. A few students didn't like the unit, but that came from the fact that it didn't feel like the rest of physics. Well, physics contains lots of different models. You're just going to like the beauty of some models more than others.

How does the Doppler effect work when the source is accelerating? We couldn't really explain it, so I made the Desmos animation above.

We also talked about standing waves. But we found music more interesting. It's so interesting to see octaves and resonance and frequency all interrelated.

What happens when wave pulses go from one medium to another? What happens at the boundary? It took many trials, and this video, to get everyone in class on the same page.

We also talked about what happened when two waves of very similar frequencies occur at the same point in space. Thanks again, Desmos:

We also talked about what happens to the frequency of a wave when the source of the wave is moving relative to the observer.

Last, we started talking about what happens to a wave that is confined to a fixed space. It seemed that, with the bounce at the end, you could get constant constructive interference. Cool!

So, what happens when a wave hits a boundary? We went to lab and saw that pretty quickly.

What happens when two waves overlap? That was more difficult. We went to lab, but we couldn't really see it that well. We had to go to simulations to understand what was going on.

I made an answer key for one of the practice sheets I found in the Modeling materials. I won't post the answer key, for obvious reasons, but I've never made an animated answer key before:

Desmos can be so cool sometimes.

"This looks like a biology worksheet."

"This looks like US History homework."

Yes, for the first time this year, I had my students do matching. Matching.

It was after we did a quick lab trying to figure out whether period or amplitude affects the speed of a wave. It wasn't a great lab. I've never gotten great results from the long springs with just pulses. But, still, it's good to play around with the wave, to see the pulse in real life, and to try to calculate its speed. 

Then I had many vocabulary words to introduce, like longitudinal wave, direction of disturbance, and trough. I wish I could get around this, but the unit of waves doesn't make coherent sense to me yet like the rest of the AP curriculum. I'm not sure what the overarching theme is. So getting through the vocabulary that isn't really that important, and doing so quickly, seemed like an OK idea.

Today was the taco party. Four years ago, one of my students left a bottle of taco sauce in my room. The bottle was brought for a fiesta in Spanish class but was never opened. The students had opened up a jar of salsa instead. So the bottle sat in my room for a while. Then I started having students turn in their labs right next to the taco sauce. Later, the taco sauce ended up on a top shelf. This year, we realized it expired in February of this year, and we planned for a taco party.

Today was the day. We had lots of sugary treats, some nacho chips and taco meat, and no plates. We managed. 

We also took a test, whiteboarded the last, relatively straightforward problems about pendulums, and played a little bit with the long slinky. We're moving on to mechanical waves tomorrow.