Archive for category Physics

Free Fall and Assessment

The bulk of this week was spent wrapping up acceleration by doing some problems with free fall.  It took some time, but my students are getting comfortable with graphical solutions instead of more traditional approaches.  Students continue to talk about what’s happening in the problem, rather than the formulas, which is great to see.  A few kids are trying to memorize formulas, but watching their peers who use the graphs apply what they know to new situations with relative ease has helped convert the memorizers.

Whiteboarding a free fall problem

Student work on a free fall problem

This week was also the first test in physics, and a lot of kids “took the bet and lost.”  Based on the reading and thinking I’ve been doing about assessment and grades, I’m grading a lot less than in previous years.  The trick is, students used to the way most teachers grade translate not graded as not worth doing.  Not surprisingly, these students were not prepared for the test.  That said, even when I’ve graded almost everything, I’ve had students find ways to copy or otherwise get out of doing the daily work, then have the first test hit them like a truck.

To try and address this problem, I stole an idea from Frank Noschese and have been giving my students weekly, self-graded quizzes.  In addition to all the other benefits of frequent, low-stakes assessments, I hoped my students would figure out the benefits of engaging in the daily work early on.  It worked for most of my students, and I saw more students digging into their work after the first quiz, but the stakes were too low for others to catch on.

I’m doing a two-stage collaborative exam for this test, so students will have a chance to recover come Monday.  I’m looking forward to seeing how that goes.  In the future, however, I’d like to work on strategies to get students away from the idea that not graded means not worth doing a lot earlier.  I may make those early quizzes worth more points (at least on paper) or split our 1D motion into separate tests over constant velocity and uniform acceleration so that students will be taking the first test a lot sooner.

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Graphical Solutions

This week, students started using graphical solutions to solve problems for an accelerating object.  I was introduced to this approach by Kelly O’Shea and Casey Rutherford at a workshop this summer.  Rather than showing my students the usual assortment of kinematic equations, I’ve been hammering what has physical meaning on a graph, especially when on velocity vs. time graphs.  When given a word problem, students sketch the motion graphs that describe the problem (especially the velocity vs. time graph) and use it as a tool to solve for the unknown information.  I didn’t get a chance to snap a picture of a student sample, but here’s a problem I did.

graphical_solution_example

I really like this approach so far.  When I’ve listened in while students were working problems, I hear very different conversations than in the past.  I used to hear a lot of talk about the formulas with students focused on either formula hunting or trying to figure out hard and fast rules for when to use each formula.  This week, I heard discussions about what the objects in the problem were doing, and what were the implications of that.  It was great to see.

Another aspect I really like about this approach is how clearly students see the connections to calculus.  I’ve had several students who took calculus last year say they are gaining an appreciation for why calculus is useful, adding a layer of richness to their knowledge.  Even better, the students who are currently taking calculus feel like they are taking what they’re learning in calculus straight into physics class.

The big challenge I encountered this week is some of my students are struggling with the demands I’m placing on them.  The graphical solutions require them to pay more attention to what is actually happening in the problem than approaches I used in the past.  Students also completed some labs and open-ended worksheets that required them to determine an appropriate approach to the problem at hand.  As a result, students spend at least some time each class period dealing with confusion or struggling with a concept.  I think this is a good thing, but a lot of students find this uncomfortable and wish the class had more direct instruction and traditional worksheets.  Students are consistently getting to where I want them to be by the end of the class period, so I think I’m on the right track  with the scaffolding I’ve been providing.  What’s lacking is a growth mindset a’la Carol Dweck.  Its time for me to re-read her book and work on explicitly incorporating strategies in my classroom to help students develop a growth mindset.

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Motion Graph Mania

This week in physics was all about making sense of position vs. time and velocity vs. time graphs.  Since I’m planning to have my students use the graphical solutions approach I learned form Kelly O’Shea and Casey Rutherford this summer, motion graphs will need to be second nature to my students.  To make sure my students have motion graphs down, I’ve dedicated a lot more time to them than the previous physics teacher did.  Based on the progress I saw this week, the time was well spent for most of my students.

The one group that grumbled a bit were my students who took AP Calculus BC last year.  I already knew the teacher, Karen Hyers, works very hard to place math content in meaningful contexts and did some work with motion graphs in her calc classes, but I hadn’t really appreciated how thoroughly she covered motion graphs.  My students who took calc with her last year easily recalled how to do just about everything I put in front of them this week.  Around 1/3 to 1/2 of my students fall into this group, so next year I want to work on some strategies for differentiation to keep the calculus students challenged.  The upside is several students commented they didn’t realize how connected physics and calculus really are.

There was also some pretty cool peer instruction that happened thanks to the calculus students.  Most groups had at least one calc student, which means someone knew what the answer should be and I didn’t have to worry to much about whether groups would get there.  However, because that person was another student, the rest of the group wasn’t afraid to question them and argue a bit before agreeing on the correct answer in ways that don’t often happen when a student is talking to a teacher.  These discussions helped many of my students to actually understand the graphs, much preferable to simply memorizing what the graphs for certain cases should look like.

But the best part of the week?  A student told me what’s hard about physics so far isn’t the content, its the way I’m making them think about it.

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A New School Year Begins

This week was the first of a new school year.  I’m trying to shift my approach this year to make inquiry a central feature of my classroom, pulling ideas from a few different sources, including Modeling Instruction and the 5E model.  Whenever someone tries to change things, some aspects will be great and some will have room for improvement.

 In the past, the other physics teachers and I have introduced constant speed by measuring the time at set positions for a bowling ball rolled down the hallway.  The lab works fairly well, but the logistical issues (including the number of people and the space needed to collect the data) mean that the lab is done as an entire class.  I wanted to have each group collect their own data and played with various options using equipment we have.  I settled on using ticker tape and dynamics carts.  Since this would be their first exposure to ticker tapes, I knew students would need instruction over how to use them.  I started with a discussion (borrowing some ideas from Kelly O’Shea) to determine we’d need to measure position and time, then showed students how to use the ticker tape to measure each of those.  I wanted students to make some experimental design decisions, so all I added is that students should have a table of their cart’s position and time by the end of the period.

It did not work.  I underestimated how much mental effort using the ticker tape would require from my students, so they had a lot of trouble dealing with the other decisions I asked them to make.  I also wasn’t explicit that students should make a written note of what they were trying to produce, so a lot of students forgot what they were supposed to do by the time they managed to get a tape with a nice series of marks.  During my first hour, I ended up pausing the lab a couple times to give some extra direction when I saw multiple groups struggling with the same issues.  In later hours, I provided a lot more structure right from the start, including prompts for students to write down information they would need to reference later.  Fortunately, my first hour students were pretty forgiving; I think it helped that I’ve talked to them a bit about the shifts I’m trying to make and why, so they saw where I was coming from.

I was pleased with how the analysis of the lab went, however.  I’d hoped to have students try creating a few different types of graphs using Plotly to get at why a scatterplot is the best option for a position vs. time graph, but I wasn’t able to get my hands on a netbook cart, so stuck with a short discussion.  My students were able to agree pretty quickly that a scatterplot was the best option and were able to articulate why.  Each group then graphed their data and performed a linear regression using either Desmos or the TI graphing calculators most of them have.  Groups sketched their graphs on whiteboards, and we had a class discussion looking for similarities and differences in the graphs.  Thanks in part to how many students have already taken AP calculus, students were able to pretty easily identify and articulate what on the graphs had physical meaning, which meant I didn’t have to deliver any lecture on constant speed.

Moving forward, I’ll save tools unfamiliar to my students, such as the ticker tape, for labs where the data collection is pretty structured, rather than try and use them for open-ended labs introducing a new topic.  This year, that may mean some compromises, such as collecting data as a class or other large group and keeping items (like motorized constant speed buggies) in mind for this spring’s order.

I also want to keep working on how to have effective class discussions.  I had several students tell me how much they loved that I lectured less than 10 minutes in the first week and I have every intention of keeping that number as low as I can.  In order for students to continue to get the content out of discussions, I need to improve my skills at facilitating them.  That will mean lots of reading, lots of formative assessment (to see if my students know their stuff), and lots of reflecting on how discussions went.

All in all, I’m excited about the shifts I’m making.  I’ve loved seeing more of my students’ thinking on display this week and they’ve been very engaged so far.  There will definitely be more hiccups and missteps, but those are just opportunities to learn.

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