# Free Fall

102 When we investigate free fall, we drop picket fences, and we also fling them upward using rubber bands. This does not work every time, but it is quick enough to get five good trials with usable slopes. We compare the slopes of these graphs to the slopes of graphs made with the dropped picket fences.

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Posted in acceleration, forces, kinematics, lab

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# Data

96 The data are starting to come in from the video analysis. Not enough yet to tell what the graph will look like. I decided to pull all the data together in a Google Doc.

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# Fan Cart

94 The conceptual classes are going to determine how much force a fan exerts on a fan cart by comparing acceleration to mass. I have never tried this before so it will be interesting to see how it works out. Each group has a video with a different amount of total mass. They will get acceleration from video analysis and then we will make a whole-class graph. Maybe all three conceptual classes will contribute data to one graph with lots of data! Ooh!

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# Elevators!

89 (Yeah, missed a few days. Last week was “Quarterly Assessment” week and was not very photogenic.) Today the conceptual classes are applying Newton’s 2nd Law to the motion of elevators. Since I don’t want any student to feel obligated to reveal their weight to their classmates, I am the one who gets to stand on the bathroom scale. We use the differences in the scale reading when starting to move and when coming to a stop (compared to standing still) to determine the acceleration of the elevator at different points in its motion. I’m wearing my favorite brown boots in this photo, and they are pretty heavy. ðŸ˜‰

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Posted in forces, Uncategorized

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# Inversely Proportional

82 We are nearly finished analyzing the data from the Newton’s 2nd Law lab. This is the first time this year that the conceptual students have had to deal with an inverse proportion, so that is new. The shapes of the graphs look nice, but we haven’t checked to see how the slope values match up with what they should be. We are not quite there yet.

This post is actually for today. Today is the 82nd day of school. ðŸ˜‰

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Posted in forces, graphing

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# N2 Lab

75 It is time for the conceptual classes to learn about the relationship between acceleration, force, and mass. We’re doing modified Atwood’s, varying total system mass first. As you can see, we are not a single-vendor school. I don’t even know where those little hanging mass sets come from, but I like them!

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Posted in acceleration, forces, lab

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# Self-Commenting

60Â Today was an assessment. I liked the winter sun streaming in on an answer key and a beaker full of purple pens, ready for students to comment on their work. I am one of the many teachers who started doing this after reading Frank Noschese’s 180 blog last year, in which he described doing this with his students. Thank you, Frank!

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# N3

56 Oops, didn’t post yesterday. Oh well, here is what we did in the conceptual classes. Newtons’ 3rd Law! I love these illustrations by Hewitt. We do these, then move on to identifying the interaction pairs on free-body diagrams.

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# Results

55Â Well, not everyone gets it yet. But, this class overall did better than the next class, which had less time to think about their mistakes and generally doesn’t discuss things at all. Purple writing is student commentary, red writing is my commentary.

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# Two for the price of one

53
I could not decide which class I wanted to talk about, so you get two photos today. The top one is from one of my conceptual classes, a great example of a mistake in which students assume that there must be some sort of straight upward force to balance the gravity force. This is the way all the FBD’s we made at first were laid out. In this problem, there should not be any surface force at all, which the system schema clearly shows. So we discussed that in class. I also spent time talking about how important this mistake was for everyone’s learning and in a later class I asked a group to add this particular mistake to their FBD, which they found distasteful but they did it anyway.

The second photo represents the successful use of Tracker to analyze a rotational motion video. I have a collection of 8 videos which I made several years ago and students have always done the analysis in Logger Pro, clicking through hundreds of frames. Ugh! Happily, last summer I learned how to use Tracker and all the groups were able to have Tracker autotrack a spot on the cardboard “record,” a process which wound up being painful in much different ways. I could go on and on about the technical issues we had but happily most of my students are resourceful and some are handy with tech support, so every group now has data to analyze. We’ll be doing that tomorrow.

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