Day 10

Physical Science: Today students continued work on the Viscosity Challenge. This lab is proving a challenge for some. Identifying variables is still an issue. Understanding that there can only be one independent variable is something that we need to work on.

Example: Some groups are trying to measure the viscosity using a setup like this one:


Here a group is finding the viscosity by timing how long it will take a marble to sink through a fluid. The independent variable is the type of fluid being used. Still, some students think that since they decided what depth of fluid to use, that this should ALSO be the independent variable, as they decided what it would be. In talking to groups (not this one by the way):

“Isn’t the depth the same for each fluid?”

“Yes it is. So?”

“Well if it’s the same for each fluid, and every test, then is it a variable or a constant?”


“What IS different? What are you changing between the tests?”

“The fluid.”

So, I think that if walked through it at this point, they can get it, but of course the idea is to get them to a point where they can identify this on their own. Knowing that my juniors and seniors in Chemistry and Physics are able to do this, lets me know that students can get there, but my Physical Science students need to be get there too. This will continue to be a point of emphasis throughout the year.

Here are some other setups being used (I hope that they images are turned when this posts. I edited it, but not sure if it worked):

Chemistry: Students got back their Mass and Change labs. It was mostly a learning experience about how to do labs. I use Active Grade to assess student learning with my SBG model. If you haven’t used it, it is a great way to set up a grade book for tracking mastery of learning objectives. I gave out a lot of feedback, in hopes of helping students get comfortable with doing chemistry labs.

So with feedback in hand, we “got back on the horse” and started another lab. This time investigating the relationship between cubic centimeters and milliliters. Students were given a plastic cube that could be filled with a volume of water, and used to calculate that volume. This same volume could them be measured in a graduated cylinder.

Not only does this lab get kids back into the lab, working on lab skills, but they are also being assessed on a variety of other skills. We will introduce a bunch of stuff off the post-lab discussion tomorrow. I’ll talk more about that tomorrow.

For tonight, students had to graph the data, plot a line of best fit, and then write a scientific line equation. I call it that, since most of my students have never written anything that didn’t have y, or x or m or b.

Physics of Light: Today we looked at our Shadows WS. This was our chance to figure out why we didn’t get penumbra’s in the lab. Students did a nice job of using the particle model we developed to explain the various shadows that were produced.

As for the penumbra, This was our first look at a problem where it can form:


The umbra, or area without any light, is the dark region behind the barrier. Here no light particles arrive, so none reflect back to our eye, and wee see pitch black. The other shaded regions though, are the penumbra. If you look at the diagram as if only “A” os present, then the umbra would extend more to the right. If you look at the diagram as if only “B” is present, then the umbra would extend to the left. When they combine, one light source casts light into those other areas, while the other light casts none. This creates an area of fewer light particles reflecting, thus it looks more grey: lighter than the umbra region, but darker than the area where all light is shone.

What about a bunch of light sources?


Similar thing here. This is meant to represent a florescent long tube bulb, which can be treated like a line of point sources. Here we see the same affect as the previous problem. A dark region (umbra) surrounded by a region where some light sources cast light, and others don’t.

This is where things get awesome.

Ss: “Would there be one area of grey, or would it be a series of different shades of penumbra?”

Me: “Hmmm…what?”

Ss: “Well at different points to the left and right of the umbra, isn’t there more or fewer light particles coming from more or fewer light sources?”

Another student: “Like that book shelf over there.” I turn and look and just below a shelf in my room I see a series of 5 different shades of grey shadows (penumbra). “Like that.”

I go over and look at it, and the kids take a look. In the room at this point there are 16 banks of light on (Middle and Back of room, front bank of lights is off) and there are shadows all around this shelf, in all different directions.

Ss: “Could we set this up and see what it looks like? Like the problem? See if we are right?”

So we took 5 5 Mini-Maglite’s (point sources) and lined up in the front of the room, sort of like the homework problem but more spread out. That gave us 5 different shadows, but basically all umbra’s since there was no overlap. Then we brought the lights in together (more like the problem) and bingo:


Shades of grey. I never thought about this before. Of course, I’ve only taught this one other time, so I admit that I have stuff to learn. My kids though, this was all them. They had the question. They had the insight to think of it. They saw examples around the room, and when I moved to do this, I had volunteers everywhere. It was pretty awesome.


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