Forces

Day 25: Redesign & Free-Body Diagrams

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Physical Science: Redesign

Now that groups have a plan for how they will test the second iteration of their design, they worked on actually planning that design. Compared the first time around, there was a lot more conversation about the different ways designs could fail. There was also a lot of talk about what had and hadn’t worked in the first iteration. At the end of the hour, each group paired up with another to share their testing plan, their design, and a justification for their design.

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Physics: Free-Body Diagrams

After a quiz, students took their first shot at drawing free body diagrams. A lot of conversations went back to yesterday’s bowling ball lab to try and decide what kinds motion did or did not require a force.

Day 24: Planning Tests & Bowling Ball Lab

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Physical Science: Planning Tests

We did some debrief on last week’s testing of the engineering design challenge. Students agreed that the single ramp test was pretty limited, so, after getting new groups, students began planning new tests that would simulate a wider variety of real-world situations. The main constraints are that the tests must be reasonable to conduct in the classroom and they will need to provide evidence on the effectiveness of the design.

Physics: Bowling Ball Lab

We began building the balanced force model today. Students hit bowling balls with rubber mallets in a lab based on Frank Noschese’s 180 blog. Some groups were debating whether the bowling ball rolled at a constant speed when it wasn’t being tapped, so we fired up Motion Shot to check.

Bowling ball in Motion Shot

Bowling ball in Motion Shot

Students looked for a pattern in their motion maps and put a statement of that pattern onto whiteboards. The statements most groups started with had some exceptions or ambiguities, but by discussing these, we were able to generate a single statement the whole class could agree on.

One group's statement of the pattern

One group’s statement of the pattern

Day 23: Design Testing & Free Fall Practical

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Physical Science: Design Testing

Today, all of my students were early and anxious for class to start. They knew that we’d be loading up their designs with eggs, then sending them down ramps to see how they did. At the end of the hour, we had a brief, but good, discussion about what it could mean to have the “best” design and the limits of the single test we used. This discussion will provide some good groundwork for our second round of designing and building.

Physics: Free Fall Practical

Students had two tasks today. For both tasks, I assigned students roles from the University of Minnesota’s cooperative group problem-solving process. First, they did a practical on free fall. Each group was given a time, and had to place tape on a strip of acrylic so that a photogate would measure the time they drew when they dropped their acrylic.

One group's solution to the practical

One group’s solution to the practical

Once groups had tested their result, they worked on XKCD’s Substitute Problem. While most groups decided to chug through the algebra, there was one that used Desmos to find the intersection of the position vs. time graphs.

One group's solution to the sub problem

One group’s solution to the sub problem

Day 22: Building & Speed Dating

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Physical Science: Building

Students worked on constructing their prototypes for the design challenge. As they worked, I visited each group to ask a random student to explain their design, especially the reasoning in their decisions. Students did a nice job of connecting their decisions to their knowledge of Newton’s Laws and energy. They also did a nice job of trying to anticipate the needs of our imaginary customer.


Physics: Speed Dating

I gave students use Kelly O’Shea’s whiteboard speed dating to tackle a goalless free fall problem. My PLC is working on how to develop our students’ mathematical communication, so I was thrilled to see the strides my students made once they knew a peer would have to follow their work. Students were also very positive and left class much more confident.

Day 21: Designing & Free Fall

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Physical Science: Initial Designs

Now that students have a basic knowledge of Newton’s 1st and 2nd Laws, they went to the drawing board to develop ideas for a design challenge where they’ll need to keep an egg safe in a head-on collision. Students had to include a justification, based on Newton’s Laws, for why they think their design will work, which lead to some good debate and physics talk within groups.


Physics: Free Fall

Students worked on some free fall calculations in groups. They are gradually getting better at using velocity vs. time graphs as problem solving tools. One of my favorite moments was when a student, who had just spent around 30 minutes working through the first problem, read the second and declared it exactly the same, in spite of some superficial differences that usually confuse students.  When I asked what she meant, the student explained how she knew the same model would apply and proceeded to point out all the underlying physics that stayed the same as a result. She was thinking like a scientist and didn’t even realize it!

Day 20: Board Meeting & Free Fall

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Physical Science: Newton’s Laws Board Meeting

Students finished collecting data, then we had a short board meeting to agree on the qualitative relationships in Newton’s 2nd Law.

Physics: Free Fall

Students white boarded answers to a few qualitative questions about last week’s Direct Measurement Video. I emphasized having them provide evidence to support their answers, which lead to some good conversations, both in groups and in the whole class, about what makes “good” evidence. Different groups looked at different combinations of falling objects, which lead to some good disagreement about whether all objects fell at the same rate. My favorite moment was when I asked whether using the same acceleration for all objects is useful and a student quickly responded with “It depends” which lead to some good talk about uncertainty.

Day 19: Newton’s 2nd Law & Constant Acceleration Practical

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Physical Science: Newton’s 2nd Law

Students began collecting data for Newton’s 2nd Law using the classic modified Atwood’s machine. This is the first time students have done an open-ended lab with quantitative data, and I enjoyed watching groups tweak their experiment to get good data.

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This group added mass to slow their cart down, then added the golf ball to prevent it from sliding around in case that impacted the motion.

Physics: Constant Acceleration Practical

Students finished the practical started on Wednesday. After we collected data as a class to determine the speed of a tumble buggy and the acceleration of a marble on a ramp, each group got a starting position for either the marble or the buggy. Groups then had to figure out where to start the other so that, when released at the same time, the marble would land in a cup on top of the buggy.

Day 18: Intertia & Free Fall

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Physical Science: Inertia

After some brief notes on inertia, students did a lab where they played with some examples and practiced using inertia to explain their observations. At the end of the lab, students had a mini-design challenge to come up with a way to keep the passenger safe in a collision. Even though we don’t go into torque in the course, it did get students thinking about where the force is applied. I intentionally left the language in the question vague, and I was pleased with the conversations students had about what it meant to keep the passenger safe.

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This group debated about the efficacy of their “seat belt” since the passenger’s “feet” still swung forward in the crash

Physics: Introducing Free Fall

We went to the computer lab for students to use a Direct Measurement Video to begin exploring free fall. This one allows students to watch side by side high speed videos of a variety of objects in free fall. I asked students to find a value for the acceleration of a falling object and to identify any variables that affects that acceleration. While many students were quick to dismiss small differences in the time, one group had a great discussion. They saw that the bowling ball fell noticeably faster than a ping pong ball, so they not surprisingly decided that weight must matter. One person wasn’t satisfied; he played the video of a large steel ball side by side with a small steel ball to show they fell at the same rate in spite of different masses and radii. With some nudging, they were able to agree that density must be the key factor.

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Day 17: Weight & Acceleration Practical

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Physical Science: Weight

Today began with some talk about the engineering design process developed by EngrTEAMS. In particular, we placed ourselves in the “Learn” phase since students agreed they need some new science to understand crashes. I introduced forces as a tool for understanding crashes, and we dove in to a lab where students used spring scales to measure the weight of several hanging masses, then graphed the results. Tomorrow, we’ll get to the idea that the slope is the strength of gravity.

Since the lab is fairly straightforward, I had the chance to do one-on-one conferences with a few students who currently have low grades to make an action plan. I’m taking an “SBG-ish” approach in the course, which means I enter unit tests in the gradebook, rather than standards, but the tests are nearly all of the grade and I allow retakes to replace the initial score. I really liked that this freed me to talk with students about missing skills and understandings, rather than a long list of missing assignments. The students also seemed much more positive about these conferences than in the past.

Physics: Acceleration Practical

For most of the hour, students started working on a lab practical where they will roll a marble down a ramp so that it lands in a tumble buggy as it drives past. As a class, we collected the data students need to get the speed of the buggy and the acceleration of the marble, then students drew a random starting position for either the marble or buggy. I introduced the practical very clumsily in my first class, so I’ll need to do some clean up and clarification when we get back to the practical on Friday.

The first part of the lesson was finishing yesterday’s whiteboard presentations and produced one of my favorite moments of the day. When preparing their whiteboard yesterday, one group made the very common mistake of using v = d/t to find the final velocity of an accelerating object. In their quick conversation, they realized their answer didn’t make sense with the other values and were able to correct it. That group was brave enough to share that mistake, as well as how they caught it, when they presented the problem.

Day 16: Engineering Design Challenge & Communicating Solutions

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Physical Science: Engineering Design Challenge

We teach forces using a project-based unit centered on an engineering desig challenge. Today, I introduced the challenge: students must make a cargo carrier that attaches to a truck will keep an egg intact in a head on collision. We spent some time today brainstorming what the customer may be interested in and what kind of background knowledge will be necessary for the task.


Physics: Comminicating Solutions

We spent some time on the importance of communication in science and connected that to what it means to show your work clearly in physics. From there, students whiteboarded the problems they worked on yesterday with clear communication in mind. This lead students to bemoan the lack of color choices in my marker bin.