Day 13

Delayed from last Thursday, sorry about that. Graded a pile of Chemistry lab books, and just didn’t have it in me to pull out my Chromebook to blog. Instead I sat down and did some heavy reading.


Yeah, I’m a comic book nerd too. More on that later.

Physical Science: Today we started in on the 2nd part of our Science Skills unit, and did a measurement activity. This activity (find it here) is adopted from the Models of Physical Science materials created at Arizona State for their Modeling Program.

Side note: I am a modeler, in case I never mentioned it. I don’t do as much modeling with my freshmen course, as I do with my Chemistry and Physics classes, but I do use it in several units.

In this activity kids make measurements using non-typical devices. They then have to figure out why their measurements don’t come out nearly as close to the other groups as they should. Here is an example data table:


Groups get pretty different results for the paper clip and tongue depressor measurements. I purposely give them various sizes of each item, but don’t say anything about it. Without really trying, the pen measurements come out fairly close, as most pens are the same size.

Two other things I’m looking at while they work is A) do they create units to go along with their measurements, and B) what kinds of estimates are they coming up with when an object doesn’t fit into a whole value.

I guess I also look at technique. Which comes up in discussion the next day.

Chemistry: We concluded talking about significant figures, and doing calculations. Not very exciting really. One of the things that seemingly ends up as a debate among colleagues every year is whether or not we should worry about sig figs.

I continue to preach sig figs year after year. I think it’s important because it makes the students think about how well they really know an answer. As we talk about in class, there are no perfect measurements. Any measurement we take, has a certain level of uncertainty in it. Plus, how good the measurement is, is based on the precision of the device we use. As kids do labs, and carry sig figs throughout, they find that the accuracy of their results can be greatly affected by this.

Plus the College Board cares. Plus college professors (some anyways) care. The first time one of mine cared about it, was Analytical Chemistry at UW-River Falls. I still remember the directions: “Make sure all answers are reported to the correct number of significant figures.”

I sort of remembered kinda hearing something about sig figs once, and managed to reason it out. It also helped that most values had 3 sig figs in them, so I just put most answers in 3.

Physics of Light: We white boarded the WS for the pinhole camera activity. The kids are doing awesome with things so far. They are using the particle model to explain how reproductions are formed by the camera. There aren’t a lot of questions during our presentations, but when there are, we get deeper, higher thinking questions. That tells me that they get it.

Of course, like any good white board session we had some really great discussion that led to some impromptu investigating. Some of the stuff we discussed:

– the role of the screen in the pinhole camera.

– Where could we put an “eye” and see the reproduction (it was agreed that if we could fit inside the camera, we could see the reproduction on both sides of the screen, but NOT if we stood in the way of the light particles. Obviously)

– What exactly is a reproduction? Well, we managed to figure out that it requires a screen, because when we take it out, there is nothing to look at. The screen can also be where ever, so long as the light particles are able to strike it.

Then we got into some interesting stuff: “Mr. Schwaller, what if we replaced the translucent screen, with something more transparent?”

“Transparent? Like how transparent? Like 100%”

“Uh sure.”

At this point I tore the screen out of one of our pinhole cameras, and said, “it would be like this.” We already say that without the screen, all we see is a pinhole of light.

“No not like, like the window in the door. It’s transparent, but we can see our reflections off of it. Would we see the reproduction then?”

Of course this meant digging for a flat, round piece of glass to put into the pinhole camera. Which I found, and put together after class. I noticed the following hour that while you don’t get the reproduction on the glass, you do still see a reproduction.

To explain, the light that comes through the pinhole may be creating something viewable, but not from our side of the glass. We only see the light that is transmitted through the glass. The light that might be reflected and create something we could see, bounces off of the glass and away from our eye. Still, some of that light does come through, and eventually hits the diffuse surface of the PVC pipe. So we do see a reproduction, but one that wraps around the interior of the tube. It is also elongated as some rays travel further into the tube before striking the surface. Still, pretty cool.

I tried to catch the student who asked about it before they left after school, and couldn’t find them. Then I found out later that they had come back to my room 8th hour, and while I was busy, found the pinhole camera, and had played with it, finding what I had.

“Wait you came back to check it out, and since I was busy you just investigated it yourself?”

“Yeah, *student* said you put it together so I came and looked.”

“And I had no idea that happened.”




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