# Day 19: Practice AP Problems and N2L Lab

Physics: Newton’s Second Law Lab. Pull a scale attached to a cart with a weight over a pulley. Record the force on the scale. Use the distance and time to calculate the acceleration, and then the net force. See that the net force is less than the recorded force. Why? Friction is a thing that exists. Seems so simple! It was a bit of a kludge.

They didn’t recognize that they had to read the force while the cart was moving, even when I told them that. They tried to do the calculations in grams and inches rather than kilograms and meters. There’s a lot that can be unpacked in that lab, especially in the choices they made, and we’re going to do some of that tomorrow, but because I re-taught projectile motion, now I’ve almost entirely missed the window for teaching Newton’s Second Law. Ah, well. N3L is pretty straightforward once you get them doing system schema, so I can makeup some time there. Still, I think N3L should come first. It’s the description of how forces happen. The other two laws are about what forces DO, which should come after how they happen.

I also asked for copies of the upcoming exam so I can see which parts I want to include and which parts I want to replace earlier this time.

Honors Physics: Continuing momentum analysis. Every group discovered conservation of momentum, like you do, but it did require some prompting and hinting that they were looking for a mathematical relationship and to focus on the bits that are moving before and after the collision. It was pretty spoon-feedy, but less so than writing the equation on the board and telling them it’s true. I still like it better than what I’ve done in the past. After the data analysis, I went over IF charts and did some practice. I did one on the board, they did one independently, and then I had them each choose one of a pair of problems and present their solution to someone who chose the other. Tomorrow is the lab, and everything I looked up required sensors, so I’ve been wracking my brain trying to figure out a momentum-impulse lab that we can do with meter-sticks and stopwatches. I found one lab with water balloons, but didn’t have time to get them, so I had my husband pick up a bunch of eggs at CostCo so I can put out a bunch of random things and tell the students they can use any of it to build any structure they want within some arbitrary restrictions I’ll figure out before tomorrow. Size restriction? Weight restriction? Number of different materials restriction? Some stuff will be restricted, anyway.

Here’s one of their whiteboards:

AP Physics: Practice Problem. I gave them question 1 from the 2016 Mechanics exam. They had 15 minutes to work by themselves and see how far they could get, and then I had them work together for another 15 minutes to see how much farther they could get. For the last 15 minutes of class I handed out the score sheet and let them self-assess using the grading rubric. Both classes had good conversations. One class had not done a practice problem before and the other had, so I was interested in seeing if there were a difference, but it turned out there really wasn’t much of one. The class that had done this exercise before was still surprised at how much the rubric focused on process rather than answers, which tells me that this is an exercise that continues to need further repeats. And the class that hadn’t done this exercise before finished much more quickly and needed a second (1M2017).