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#AAPTSM18 Recap #1 – “Can We Have a Group Test?”

Saturday July 28

“Can We Have a Group Test?” Designing Collaborative, Active, Alternative Assessments for Physics Classes (Kelly O’Shea, Danny Doucette)

On Saturday, I attended Kelly O’Shea’s and Danny Doucette’s all-day workshop on lab practicums. All of their slides and handouts are here: AAPT Collaborative Group Practicum Exams Workshop.

For the first half of the day, Kelly and Danny had us in “student mode” as we performed several of the practicums in groups and then shared our experiences with the rest of the participants.

There were two rounds of practicums. Round 1 had practicums on friction, kinematics, and energy.  Round 2 had practicums on calorimetry, internal resistance, two-slit diffraction, and rolling projectiles.

After lunch was dedicated “work time” where we had time to work on developing new practicums of our own, either alone or with others. One group of participants, led by Val Monticue, developed a generalized grading rubric for practicums. I worked on two things: (1) designing a new practicum with several other teachers that ties together energy, momentum, and friction; (2) designing “leveled practicums” with Jenn Broekman.

The set-up for the new practicum is an adjustable pendulum with a 100-gram bob that swings down and strikes a 100-gram tissue box (mostly empty), which causes the tissue box to slide across the table. The practicum has 2 parts: (1) Vary the release height of the pendulum so that the pendulum comes to rest upon impact with the tissue box. (2) Using the data from the first part, predict the necessary release point of the pendulum so that the tissue box slides a given distance (preferably so the the box reaches the edge of the table, but does not slide off).

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A lot of time was spent figuring out what size/mass the pendulum and box had to be so that the box slid a decent distance when struck by the pendulum. At first, we tried a small block several centimeters thick. The block had tendency to spin when struck, and sometimes the pendulum swung over the block. Then we tried a larger wood block. While it was tall enough that the pendulum didn’t swing over the block after impact, it didn’t slide very far due to its increased mass. Finally, we discovered that a tissue box worked really well — tall and light. Coincidentally, the mass of the mostly empty tissue box and the pendulum bob were the same (100 grams).

Once we got the set-up working, we put the practicum to the test to see if it would actually work. First we found the “sweet spot” when the pendulum comes to rest after striking the tissue box. Based on the release height of the pendulum and the distance the tissue box slides after impact, would could calculate (1) the speed of the pendulum right before hitting the box; (2) the speed of the box immediately after being hit; (3) the coefficient of friction between the box and the table; (4) the percentage of kinetic energy lost in the collision. Assuming the percentage of kinetic energy lost is the same in all collisions between the pendulum and the box, we calculated the pendulum release height needed for the box to slide 1 meter. Our predicted height (~40 cm, if I recall correctly), was much larger than the actual height needed (~80 cm). So while it didn’t work, we think that the practicum was still fun and challenging and tied together lots of different topics. Having students reflect on their assumptions and explain why the actual height is larger than the predicted height would be good, too.

For the remainder of the work time, Jenn Broekman and I turned the traditional constant velocity lab practicum into a “leveled” practicum. We got the idea from Kelly O’Shea that day, who suggested redesigning practicums so that all students could feel successful. Jenn and I broke the buggy practicum into 3 levels (easier, regular, more challenging). Here’s what we came up with:

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We think these could be deployed in several ways. One option is for all students to start with Level 1 and work through as many as they can in the time allotted. Hopefully by the end of class, all groups will have completed at least the Level 1 task. One drawback to this deployment is that it’s possible that some groups that would be successful with Level 3 would never get a chance to try it because they spent most of class time working on Levels 1 and 2.  So another deployment possibility is for students to chose the level of task they feel most comfortable with first. In this case, a group could start with Level 3 and spend all class period working on it and be successful in the end, while another group might need all period for Level 1, and another group might start with Level 1 and then move on to Level 2.

After work time, everyone shared what they worked on. Here’s a practicum developed by another group. It’s about electromagnetic induction:

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After the workshop, I walked back to my hotel, which took me past the White House. There were several protesters there, and a person dancing and wearing a Trump mask.

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More updates about the rest of the conference in future posts!

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Day 65: Hour of Physics Code

This gallery contains 4 photos.

Originally posted on Noschese 180:
College-Prep Physics: I’ve been coding with my AP Physics classes for years. But in honor of this week’s Hour of Code, I tried VPython programming for the first time with my College-Prep class. We used the GlowScript version…

Day 26: What Causes Gravity?

Readers of Action-Reaction may be interested in this recent post on my 180 blog.

Noschese 180

College-Prep Physics: Even though we now have a mathematical relationship between mass and weight, we still don’t know what causes Earth’s gravitational pull. So first, we took a short survey:
GravitySurvey
Download a copy here: GRAVITY Survey 2015

Then we went through each of the four claims in survey question 4 and did a testing experiment for each claim.

CLAIM #1: Earth’s Magnetism

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CLAIM #2: Earth ‘s Rotation

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CLAIM #3: Air Pressure

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CLAIM #4: Earth’s Mass

We also compared characteristics of different planets using a table of planetary data.

This sequence of claims and questioning is based off one found in Preconceptions in Mechanics. On Tuesday, we’ll discuss the relative strengths of the gravitational pulls that 2 masses exert on each other.

##BFPM

NGSS Science and Engineering Practice #6. Constructing Explanations 

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Day 16: Relative Motion

Readers of Action-Reaction might be interested in today’s post from my 180 blog.

Noschese 180

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College-Prep Physics: This year I decided to bring relative motion into my curriculum. It’s a unit in Preconceptions in Mechanics, a book I used a lot last year for introducing different types of forces. My hope is that vector addition of velocities (which can be easily demonstrated, see below) will help some kids understand that vector addition of forces act the same way.

I modified the lesson cycle from the Preconceptions in Mechanics, Unit 2Day 1 Lesson.

I started off the lesson showing the first 15 seconds of of this Japanese video in which a baseball is shot at 100 km/hr out of the back of a truck moving in the opposite direction at 100 km/hr (you could even do the first 3 minutes if you’re evil):

They’re hooked. “What happens?”

Next, I handed out the voting sheets. Here are the slides with my questions for each stage of…

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Day 13: A New Approach to Colliding Buggies

Today’s 180 blog post that Action-Reaction readers might be interested in….

Noschese 180

College-Prep Physics: Modeling Instruction’s standard lab practicum for the constant velocity unit is colliding buggies. Lab groups take data to determine the speed of their buggy, then the buggies are quarantined and groups are paired up. Each group pair is then given an initial separation distance for their buggies and are asked to predict the point were the buggies will collide. Once they calculate the answer, they are given their buggies back to test their prediction.

It’s fun, but there are some frustrations. Groups that have poor experimental design or data collection techniques won’t calculate the correct buggy speed, which means they won’t accurately predict the collision point. Also, since only the separation distance is given, there isn’t much focus on the position of the buggy and students are less likely to use a graphical method to find the collision point. They try all sorts of equations instead. In the end, one person in…

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Flappy Bird Physics Is Real Life?

If you don’t already know, Flappy Bird is the hot new mobile game right now. The premise is simple: navigate the bird through the gaps between the green pipes. Tapping the screen gives a slight upward impulse to the bird. Stop tapping and the bird plummets to the ground. Timing and reflexes are the key to Flappy Bird success.

This game is HARD. It took me at least 10 minutes before I even made it past the first pair of pipes. And it’s not just me who finds the game difficult. Other folks have taken to Twitter to complain about Flappy Bird. They say the game is so difficult, that the physics must be WRONG.

https://twitter.com/ThatPuckBeaut/status/428781313433149440

https://twitter.com/maaddawwg/status/427833802140815361

 

So, is the physics unrealistic in Flappy Bird?

Sounds like a job for Logger Pro video analysis! I used my phone to take a video of Flappy Bird on my iPad. To keep the phone steady, I placed it on top of a ring stand with the iPad underneath.

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(I’ve uploaded several of the videos here if you’d like to use them yourself or with students: Flappy Bird Videos.)

Then I imported the videos into Logger Pro and did a typical video analysis by tracking Flappy’s vertical position in the video. Sure enough, the upside-down parabolic curves indicate Flappy is undergoing downward acceleration.

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But do the numerical values represent normal Earth-like gravity or insanely hard Jupiter gravity? In order to do this, we need to (1) set a scale in the video so that Logger Pro knows how big each pixel is in real life and (2) determine the slope of Flappy’s velocity-time graph while in free fall, which is equal to the gravitational acceleration.

The only thing we could realistically assume is the size of Flappy Bird. If we assume he’s as long as a robin (24 cm), then the slope of the velocity-time graph is 9.75 m/s/s, which is really close to Earth’s gravitational acceleration of 9.8 m/s/s. Flappy Bird is REAL LIFE.

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So then why is everyone complaining that the game is unrealistic when, in fact, it is very realistic? I blame Angry Birds and lots of other video games. Repeating the same video analysis on Angry Birds and assuming the red bird is the size of a robin (24 cm), we get a gravitational acceleration of 2.5 m/s/s, which only 25% of Earth’s gravitational pull.

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In order to make Angry Birds more fun to play, the programmers had to make the physics less realistic. People have gotten  used to it, and when a game like Flappy Bird comes along with realistic physics, people exclaim that it must be wrong. As one of my students notes:

 

UPDATE 31 Jan 2014:
Inspired by a tweet from John Burk,

we made a video showing Flappy Bird falling at the same rate as a basketball:

Here’s what I did: We determined from the analysis above that Flappy Bird is about 24 cm across. Conveniently, basketballs are also about 24 cm across. So I had my physics teacher colleague Dan Longhurst drop a basketball so I could video it with my iPad. Dan just needed to be the right distance away from the camera so that the size of the basketball on the iPad screen was the same size as Flappy Bird on the screen (1.5 cm). Next, I played the basketball drop video and Flappy Bird on side-by-side iPads and recorded that with my phone’s camera. Once I got the timing right, I uploaded the video to YouTube, trimmed it, made a slow motion version in YouTube editor, then stitched the real-time and slow motion videos together to create the final video you see above.

UPDATE 1 Feb 2014: While the gravitational acceleration in Flappy Bird is realistic, the impulse provided by the taps are NOT realistic. Here’s a velocity-time graph showing many taps. When a tap happens, the velocity graph rises upward:

FlappyBirdConstantPostTapVelocity

As you can see, no matter what the pre-tap velocity (the velocity right before the graph rises up), the post-tap velocity is always the same (a bit more than 2 m/s on this scale). This means that the impulses are not constant. In real life, the taps should produce equal impulses, which means that we would see that the differences between pre- and post-tap velocities are constant.

TL;DR: Is the physics in Flappy Bird realistic? Yes AND no.
YES: The gravitational pull is constant, producing a constant downward acceleration of 9.8 m/s/s (if we scale the bird to the size of a robin).
NO: The impulse provided by each tap is variable in order to produce the same post-tap velocity. In real life, the impulse from each tap would be constant and produce the same change in velocity.

UPDATE 1 Feb 2014 (2): Fellow physics teacher Jared Keester did his own independent analysis and shares his findings in this video:

 

What Happened When I Gave Them the Answers

Reblogging today’s 180 blog post to Action-Reaction in order to try to get more feedback from folks. Click through to read more and leave comments over there. Thanks!

Noschese 180

[TL;DR – Not as much as I had hoped.]

College-Prep Physics: Students came to class with the following question completed for homework:

You are on a sleigh ride in Central Park one brisk winter evening. The mass of the sleigh with everyone in it is 250 kg, and the horses are pulling the sled with a combined horizontal force of 500 N. The sled moves at a constant speed of 3.33 m/s.
(a) What is the force of kinetic friction on the sleigh?
(b) What is the coefficient of kinetic friction between the sleigh and the ground?

I asked everyone to whiteboard their answers. I heard some students say they didn’t get it. Several other students came up to me — worksheet in hand — to ask if their answer was right.

“I’m going to give you the answers,” I said. “Here they are.”

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“Now on your whiteboards, I want…

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