New Centripetal Force Lab

The growing pains of collecting data by using the stopper lab for the circular motion unit is well known to a number of teachers. In the modeling workshop I attended at ASU, everyone was forewarned of how difficult it was to collect good data, and sure enough, it was messy. So I have been on the lookout for different approaches to introduce the circular motion (central forces) unit.

Central ForcesI was really happy when I came across Casey Rutherford’s great idea of collecting data by using an accelerometer (Labquest 2s) strapped to a spinning chair. Check out his blog post. He also has great ideas on how to introduce the topic, which I have borrowed as well. So I tried using the chair to collect data, but I was having trouble getting the smooth spinning motion. Then I decided to pay a quick visit to the art room, and there I found out I could use a low friction sculpting turntable instead of a chair as my set up. For measuring the acceleration, I used Vernier’s Wireless Dynamic Sensor System, and it worked better than I expected. Here is the whole thing doing its job:

To measure velocity, some students timed the period of rotation, while others used a photogate. I test drove this lab before trying it with the students, so here is the data I collected. I changed the velocity and measured its effect on the acceleration:

Acceleration Vs. Velocity

Then I squared the velocity for linearization. Then students were able to derive the equation for centripetal acceleration, with the slope being the inverse of the radius. The results were great.

Acceleration Vs. Velocity Square

I’m really satisfied with this new approach to the circular motion lab, and I no longer have to tell students that the data may or may not work. I am definitely using this method again next year.

On Learning and Assessment (Part II)

This is part two of a two part series on learning and assessment. My goal is to share a little bit what I have recently learned about grading/assessment (part I) and to reflect upon my own practices (part II).

Searching for Assessment’s Sweet Spot

We are products of our own experiences, so I assessed students mostly the same way I was assessed in school. Not good! I knew I needed to change, but like most teachers, I had/have fears too, so changes were slow. Here are some of the changes I have implemented in my classroom and some of my current views on grading and assessments:

  1. I do not grade homework. I also prefer to call it practice. Soon after I made that change I also stopped assigning grades for homework completion. I didn’t see the point. Most of the time I’m not even sure who actually did the work, if the student, a tutor, or a friend. Since then, I haven’t really noticed big changes in students’ attitude towards work outside of the classroom, it continues to be poor.
  2. I do not factor work habits grades into students’ academic grades. I did for the longest time, but not anymore. I don’t penalize students for not submitting assignments nor for late submission. I don’t give students extra-credit and/or bonus questions on assessments. I believe we should report students’ learning dispositions apart from their academic achievement.
  3. I do not count quizzes nor any other form of formative assessment against students’ grades. I don’t want to punish students as they navigate the learning process. I’m interested in the final outcome. Initially kids are confused about this, but in the end they wouldn’t have it any other way. Not counting doesn’t mean I don’t report; I still share their performance in the gradebook so parents and students can gauge progress. I want weekly quizzes to be about feedback, focused on the learning . . . not about grades. Students also “grade” their quizzes, because I want them to get in the habit of self-evaluation, and I want them to have immediate feedback. I find this approach very friendly to both students and teachers.
  4. End of unit exams (summative assessment) count, and are what I use to determine students’ grades. But I also give students multiple opportunities for reassessment, independent of the grade they have earned. They are all allowed to reassess if they so wish, but the latest evidence (for better or for worse) is what matters and the one that counts for their grade.

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On Learning and Assessment (Part I)

This is part one of a two part series on learning and assessment. My goal is to share a little bit what I have recently learned about grading/assessment (part I) and to reflect upon my own practices (part II). 

Learn. Learn. And Learn Some More.

I have been thinking a lot about assessment and learning these days. My current school is in the proto-stages of completely overhauling the assessment and reporting systems, and I find no better time to dig a little deeper into the subject and reflect honestly about my practices. It is a little embarrassing it has taken me so long to carefully read, study and reflect on my assessment practices, especially considering how vital assessment is to learning. Up until this year, I had not put in enough time and/or effort into learning about something so crucial to my profession, so I finally decided to change things and made the conscious decision to learn more about assessment. Right now I’m on this on-going learning quest trying to understand how assessment can support and improve student learning. So just this last month I read two books on the subject and I’ve got a third book already lined up, ready to be purchased. Continue reading

Desmos and Mathematical Modeling

I first heard about Desmos on Twitter. What an incredible graphing tool. I don’t think any teacher forgets the first time he/she introduces desmos to the classroom; you can feel the room buzzing with excitement. Just amazing. So every year I look forward to the day I introduce my students to graphs and Desmos.

Unlike a lot of physics modelers, I do take the time to go through “unit zero” (scientific reasoning) with my students in Introductory Physics. Perhaps the reason is because I like the development of the linearization concept in graphs (very useful for my IB students), perhaps it’s because I like to kick off the class with the spaghetti bridge lab, or possibly it’s a combination of both. The funny thing though, is that every year I introduce students to graphing in a different way, and I’m always uncertain of the best way to do it. While I have had students produce graphs by hand, I always questioned the validity of hand-drawn graphs in the digital age. I have also tried digital tools like: Continue reading

Drive. We Need Motivation.

Note: This is the first post in a series on professional books I’ve committed myself to read over the course of the year. Twelve books–one for each month of the year–that’s my goal. This post is a short account of my impressions of the book, from an educator’s perspective.

Book # 1:  Drive: The Surprising Truth About What Motivates Us by Daniel H. Pink.

DriveI can’t recommend this book enough. Does increased motivation sound good to you? I read this book this past January, but the topic is even more relevant now that we’re at the end of another academic year, a time educators are searching for any motivation that’s still left in them. My first exposure to the book was by means of RSA’s entertaining animation of Pink’s work. This short video addresses the main ideas covered in the book. If you haven’t seen it yet, you should. Right now.

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Blog. Why?

Have you heard yourself telling your students, “Don’t just sit there . . . do something!” I know I’m constantly asking my students to create/contribute, maybe because I believe in the learning inherent in the creation process. Whether creation means a blog post, video, spreadsheet, science fair project or something else, I want them to contribute to society. It’s not that I believe society will be the great beneficiary of what they produce (although this certainly can be true), but because they will be better students and more responsible citizens for having produced something. Continue reading