As explained yesterday, today was about practicing with the charge model. We were still WB’ing the practice sheet, but that went hand-in-hand with drawing a series of pictures for conduction and induction, and each student having an opportunity to charge an electroscope with each method:
Well, I really like the Hot Wheels activity for energy conservation… after all, who does not love to play with the little cars? The issue for some today was that the kinetic energy at the bottom of the ramp, had a greater value than the gravitational energy at the op of ramp… not so Hot. So is the error with the determination of the change in height or the velocity?
I think I figured out the issue. I was using a single photo gate with ‘One Gate Timing’ to get the instantaneous velocity of the car at the final height. I’ve used a single photo gate successfully over and over and over and over …. it’s one of my favorite uses of the photogate. When I run the experiment, no issues, but when some of my generals did it, they must have measured the ‘flag’ incorrectly. It is a narrow flag to give a better value for the instantaneous velocity, but even a millimeter off makes a difference when the energy values are so small to start with. Tomorrow I will try a different photogate, one with no flag needed… a Bee-Spy photogate. I am pretty sure the cars will fit through. Stay tuned…
The class did two things today, well, I did one and the class did the other. We discussed the conceptual part of their summative impulse and momentum test. All of my tests have two components; a conceptual part which is mostly multiple choice (at a higher DOK than simple recall) and a problem set. The conceptual part is usually about 10 or 15 MC and there are usually one or two problems depending in how many objectives being assessed. On this recent test, there was an impulse problem and a conservation of momentum problem. On each test I also provide an opportunity for the students to really challenge themselves by providing a choice of two problems that both address the same objective. For example, on this recent test the student could choose to do a pretty standard run-of-the-mill explosion problem or a ballistic pendulum problem.
This time we did not discuss the problems. Rather, I am going to have the students make corrections on the problem(s) they will re-assess in addition to some posted practice problems.
After discussing the multiple choice component we moved to WB’ing the practice sheet putting all the components of the charge model together. We really did not get so far, only through the series of pictures to explain charging by conduction. We will finish it tomorrow.
We had a practice COE assessment and the started a COE activity that has two parts. The activity is based on this problem from the assigned practice:
The basic premise is whether or not 10% dissipated is a realistic value. To test it, we are using Hot Wheels and track to recreate the problem. Essentially, they will solve for the Energy dissipated by taking the difference between the initial gravitational energy and the final kinetic energy. The velocity is measured at the bottom of the track/ramp with a photogate.
The follow-up will be to have the students use the values from this part of the activity to predict the velocity of the car at some spot along the ramp that I place the photogate.