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.
As mentioned last week, today was a data gathering day for the radial acceleration experiment. The purpose was to determine the relationship between radial acceleration and tangential velocity. They used a single photo gate (One Gate Timing) to measure the tangential velocity and a Vernier WDSS to measure the radial acceleration. They set it up to measure only the x-axis acceleration. The radius was held constant, but the experiment was completed at a second radius. Here are a few clips of the data being gathered.
Tomorrow will be all WB’ing.
Today we reviewed a bit about drawing force diagrams with components. So far, we had only worked on tension forces that had components. Today we extended this to when we have an object on an incline. Years ago at a Phox Share meeting, Dale Basler shared a demo using the Vernier WDSS to show the force diagram for an object on an incline. The file is set-up with animated vectors to show the gravitational force, the normal force and a tension force, but they are really the accelerations in those directions. It is really slick and does an excellent job of showing the kids how the forces (size and magnitude) change (or not in the case of the gravitational force) as the incline is increased. Here is a clip of it in action.
As I explained on Thursday, the students completed a short circular motion force diagram assessment:
Today, after we discussed the possible solutions (depending on how the system was defined) we talked about how nice it would be if we really ha such a thing… like a giant merry-go-round-of physics instead of the mini-merry-go-rounds (ie record players we have been using with our experiments). Well…. we do:
SIDEBAR: I apologize for the video quality, I tried to use the ‘blur faces’ feature of YouTube, but it’s a bit difficult to blur as they ride the circular path.
The original idea and design details were shared at one of our Phox Valley Physics and Physical Science Share Meeting (many years ago) by a former member who no longer teaches in the region. As you can see in the clip, we also use a Vernier Lab Quest 2 to measure the radial acceleration. It is configured to measure on the x-axis acceleration. We also have the student play catch as the ride (shown in the second part of the clip) and shoot some baskets. This was all we had time for today; you guessed it, another early release day with only 30 minute classes.
Today the students took an assessment on drawing circular motion force diagrams. Here is what I gave them:
You’ll see why tomorrow.
We also had a pre-lab discussion to develop and experiment that will allow us to quantify radial acceleration. Through discussion, we arrived at looking at the relationship between radial acceleration and tangential velocity for a given radius. Most kids decided that the radial acceleration would be affected by the angular velocity, the radius and the tangential velocity. I asked if we could do an experiment where we varied the radius. A few realized that it was not possible because varying the radius will also change the tangential velocity *if the angular velocity is not changed)… so simply moving out on the circular to change the radius also changes the tangential velocity.
Here is the experimental set-up being used:
That’s a Vernier WDSS zip-tied to a meter stick on our record players. The tangential velocity will be measured using a Vernier Photo gate and One-Gate timing. The students will do the experiment twice… a small radius and a larger one. We did not get finished, so more data collection later. Here is a screen shot on my own data:
Today we discussed the rotational kinematics assessment the kids took on Friday. It continues to amaze me that even after a full semester with me, most of my students still reach for the equations….Here is problem I gave them on the assessment
It is REALLY easy to solve with an angular velocity-time graph, but tougher and longer with the equations… sigh.
We also looked at sample tangential velocity problem I asked the students work on over the weekend.
That’s a picture of some wind turbines all my students have seen many, many times. I asked them to determine the speed in miles/hour for the tip of the blade. I provided them with the pdf of the design specs. The blade length is 134 ft and the operational rate is 14.4 rev/min….. the answer surprises most 138mi/hr.
After that we developed the concept of radial (or centripetal) acceleration. I prefer radial because they are less likely to confuse it with centrifugal AND we hit a vertical circle we can discuss a tangential acceleration more easily.
We WB’ed the same set of motion pillars we used with the Advanced class. I had 3 groups CYOP (create your own problem). One I used as an exit formative assessment, the other twoI will use as additional formative assessments. We also just briefly started discussing how to draw force diagrams. More on this tomorrow.