A friend of mine runs the SADD group here (Students against destructive decisions), and I loved that the members of this fairly large and active group all wore a shirt with this powerful quote.
Also, last day before break. I love teaching physics, where a good lab keeps students engaged for the last 2 hours before freedom!
A recent development that I attribute (once again) to Modeling Instruction is the willingness of students to help each other. Love it.
Bonus Pic #1: An awesome physics folder!
Bonus Pic #2: Christmas gift! With an awesome thank you card attached.
Today (ok, you got me, it was yesterday…a bit behind here) We white boarded a horizontal launch projectile motion problem for the first time. The students rocked it, I was surprised at how easily they seemed to be ok with separating the X and Y directions despite that I didn’t really talk about it. Another score with Modeling Instruction, plus the fact that MI does projectile motion after forces. Anyway, at some point in each class a discussion came up about using the initial velocity in the y direction; with the launch velocity of 10 m/s horizontally, should the initial velocity in the y position equation be zero or 10? They were able to resolve to zero well. So after solving for time of fall, I raised my hand. “So you’re telling me, if I drop a bullet and shoot a bullet horizontally at the same time, they’ll land at the same time on horizontal ground?” I tried arguing against it, but they wouldn’t have it. Yep, they said, they land at the same time. “I sure wish the Mythbusters had explored this…oh, wait.” So we watched this 3 minute clip of the end result of their demonstration. It bothers me a little that the difference is 36 ms, that seems large to me considering all the pains they took in making sure the bullets drop at the same time…but it is convincing enough to students that they should land at the same time. We also have a quick conversation about sources of uncertainty that cause that difference; they always think it’s that they aren’t dropped at the same time despite the high speed video showing that the drop time difference is 1/3 of a ms. I suspect a combination of a not perfectly horizontal shot and a not perfectly level ground, but that’s just my suspicions.
Today we rolled balls off a table. I had intro’d the plan yesterday by asking students about how we can investigate an object flying through the air. We talked about how motion detectors are fairly useless, but they remembered way back when (mid September, I would guess) when we did a bit of video analysis for CV and CA before switching to motion detectors (I start CV with the CV buggies with penny drops to mark postions at equal time intervals, so I liked using video analysis right after that because the clicks are essentially penny drops). They figured video should work well.
I had them start clicking before the ball actually left the table. This made it very evident that the X position graph stayed linear with the same slope and the X velocity graph stayed constant at the same values. They picked up on this right away in the whiteboarding circles. It didn’t take them too long to figure out that the Y direction can be modeled with CA and that the acceleration should be 9.8 m/s/s.
The best part was when they stated X velocity was constant and I asked “Why?” (and probably made a pun about Y at the same time…). Because there are no forces in the X direction. You mean the forces are balanced in the X direction? Yep. They were able to use the same logic at that point show why theory says that the acceleration in the Y direction would be 9.8 m/s/s based on the free body diagram. Again, I love connections!
Some action shots for fun.
A student before rolling the ball
While the ball flies (see the blur?)
Students analyzing the data
For months now we have created a new calculated column in LoggerPro to deal with the fact that time is not zero when we start our analysis. I have them use this method instead of the checkbox possibility because I think it is easier for students to understand what we are doing…we are manually forcing the initial time to be zero. Today they were given a problem were a villain dropped a canister of poison gas and half a second later the hero pushes off downward to grab it (conveniently he can attach himself to a bungie cord in that time, go figure). Thus students have to find a way to algebraically figure out a way to deal with the fact that the two constant acceleration motions start at different times. One student said something along the lines of “it’s just like when we time-adjust, but we can do it in the equation like this.” I love when they make connections!
Meredith (the student hold the paper and clearly doing the explaining) has struggled some in CIS Physics, yet was excited today that she understood the question and felt confident enough to take the lead in the whiteboard presentation.
(Warning: Slightly trivial post!) This year we started using Auspen refillable whiteboard markers. They have been great…except that for the last month or so they seem to dry up almost instantly. I have been messing with them off and on when I felt I had time, and I concluded last week that they had gotten dry enough that when we refilled it wasn’t really re-saturating. So I tried adding much more ink than normal, but they still seemed to run out quickly.
Today I pulled the insert out of one that I thought I had saturated (I put at least twice the recommended 20 drops in), and found that there was a very clear gradient such that the bottom was not even close to saturated (hopefully you can actually see that in the picture). So I really saturated it this time, we’ll see if that works.