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:
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.

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

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 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…

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…

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.

Somewhere Mr Bourne is telling some kid that the physics on Flappy Bird is all wrong

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.

(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.

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.

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.

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:

@fnoschese looks like those sorry folks need themselves some logger pro

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:

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:

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!

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.”

That type of rhetoric frequently appears in my Twitter stream. My gut reaction is hell yeah. But some recent quiz results have gotten me thinking ….

Take for example, this learning objective: The student understands the difference between mass and weight.

Here’s a student project (not mine) which clearly addresses the objective.

Here’s another project (also not mine). This one is very creative and totally adorable.

But those two projects are really just rehashes of the traditional explanation of the difference between mass and weight: “mass is the amount of stuff an object has and doesn’t change, while weight is the gravitational pull on an object and can change depending on location.” I wonder what would happen if those two students encountered quiz questions like the ones below. Would they make the same mistakes as several of my students did? I feel that even though my students can parrot back the difference between mass and weight (like in the above videos), they don’t really understand that difference if they miss these type of quiz questions:

I did find one project where a student (again, not mine) gives a thorough explanation and uses several examples. I predict that this student should be able to answer those quiz questions.

What I’m trying to say is that I feel that teacher-generated questions and experiences (quizzes, labs, whiteboard problems, etc.) are important because they challenge students to think and apply in ways they probably wouldn’t if we just left them to their own devices.

But I also get that projects let students be creative and allow them to demonstrate their understanding in ways that quizzes simply can’t.

Perhaps the answer is just “all things in moderation.” Or perhaps the project parameters need improvement so students aren’t simply reciting Wikipedia definitions from a Powerpoint? Or something else?

I’m not a PR guy. I’m just a teacher. But they say that if you want to be a disruptor, the best experience is no experience. So here goes…

1. It’s not about the technology. It’s about what students are empowered to do because of your technology. Show us how you take students beyond what they could do previously. Show student work (“Hey, look what this kid can do!”). Stop focusing on checkmarks, badges, data, dashboards, and slick UI.

2. Learning is social. Show students interacting with each other, questioning, helping, constructing — all as a result of using your technology. Don’t show kids glued to screens, headphones on, working en masse and in isolation. It’s creepy.

The Learning Lab at a Rocketship school, where students spend 2 hours each day.

6. Run controlled, peer-reviewed experiments that use conceptual diagnostic tests to measure growth. We know most anything works better than (or as well as) passive lecture instruction. But how does implementation of your technology stack up to other evidence-based teaching methods? And be sure to use conceptualdiagnostictests, not final exams or standardized tests or failure rates. CDTs have been painstakingly researched and designed to measure true conceptual understanding rather than algorithm memorization. Without strong evidence, we’re just skeptical of your claims.

Hake’s analysis of 62 different physics courses as determined by gain on a physics conceptual diagnostic test.

7. Don’t contradict yourself. Your words should match your actions.

8.Show feedback and testimonials from students. In particular, have students demonstrate their deeper understanding and expert thinking that has been enhanced by using your product. Or perhaps your technology has decreased student anxiety and contributed to a positive classroom climate. However, don’t have students talk about shallow things such as raising grades and doing well on tests.

Testimonials from Pearson/Knewton’s MyEconLab

9. There’s nothing revolutionary about old wine in new bottles. A digital textbook is still a textbook. A video lecture is still a lecture.