As part of the Educator Effectiveness project, we are required to survey the same set of students, twice during the course in which we instruct them. So, today before WB’ing the results of the radial acceleration experiment, I ask the Advanced students to complete the second survey. It has to be the same set of questions we gave before. There are 10 or 12 questions we must ask and can not edit, and we are allowed to give more. I used a google form again because I really like how the results can be displayed. There are always some interesting stats that pop out at me. For example: 2 students (of 66) disagree or strongly disagree that I am knowledgeable about the subject I teach, a total of 6 students disagree or strongly disagree or don’t know if the lessons I plan are engaging. I did learn that I have something to really work on… allowing students to demonstrate knowledge in a variety of ways (21% disagree, strongly disagree or don’t know). This will be something I will try to work on throughout the rest of this year and into next year. Any ideas on alternative assessments would be appreciated.
We WB’ed the radial acceleration experiment. Next year I will alter how I do this… probably have the students pick a radius and monitor the radial acceleration as the angular velocity is varied. I have not done that in the past because I have always felt that if students look up the equation for radial (or centripetal acceleration) they will see ar=vt^2/r.
We also started a sample problem. Here is a clip of it.
The students will have the mass, the angle with the horizontal, and the length of the string. We are going to solve for the time it takes to complete 10 revolutions, then check it of course.
More force diagram whiteboarding. At the close of the hour I asked the student’s to provide me with their color. Most students in my 4th mod class were yellow (needing more practice) and in 7th most were green. So tomorrow, with Mod 4, we will do some small group work (groups based on color) and in7th, we might play the mistake game as described by Kelly O’Shea here.
The plan for today was to WB a WS that had 7 stack-o-graphs. For the first 5 problems, the given information was a ramp and tower set-up. Here is an example:
The students created the position, velocity, and acceleration graphs. I call them ‘stack-o-graphs’ because I like to stack them vertically like this:
For the last two problems, the students are given the velocity-time graph and asked for the other two graphs AND the ramp setup to produce the graphs.
I use this sheet to provide practice for the kids sketching the graphs and to develop the sign convention for velocity and acceleration. After each problem is presented, and we have answered any additional questions, we add a general statement about what is happening to the object (getting faster or getting slower) and the sign on the velocity (+ or -) and the sign on the acceleration. It does not take very long for the students to see a pattern: If the object gets faster, the signs on the velocity and acceleration are the same and if the object slows down they are opposite. We then extend this to the velocity and acceleration vectors point in the same direction or opposite direction. I still like to WB this type of practice because during the explanation, one or more students usually say something to the effect that the acceleration is negative because the object slows down (if when they it could, be slowing with a positive acceleration).
SIDEBAR: I was tempted to play the mistake game that Kelly O’Shea has developed (explained here) but was concerned that some of the students may not have understood the kinematic stack -o-graphs well enough to realize the mistakes… maybe that is the point though.
As promised, here is the set-up for the two-way mirror demo.
Last week we work with planar mirrors. Today started our transition to curved mirrors. I used a bridging activity similar to the one we did with curved refractive surfaces. Here is what it looks like:
To check the predictions (once the students have discussed it in pairs), we use our Craftsman laser levels magnetically attached to the big WB, with planar mirrors. This activity does a really nice job of building the concepts a converging mirror and diverging mirror, and showing where the focal point for each is. Tomorrow we extend it to predicting the image characteristics with ray diagrams, then checking them with the actual mirrors.