I Was Wrong About #BottleFlipping

I didn’t think there was a useful K12 math objective in bottle flipping. My commenters served their usual function of setting me straight.

I was asking the question, “Can you predict whether or not a bottle will land?” A modeling problem.

Commenters like Meaghan asked the question, “What conditions will set yourself up for success in bottle flipping?”

How much water in the bottle? What kind of angle on the toss? Clockwise or counterclockwise? These are statistical questions.

Paul Jorgens followed that angle with his class:

It started with an argument in class last week about the optimal amount of water in the bottle. Should it be 1/4 filled? 1/3? Just below 1/2? I told the group that we could use our extra period to try to answer the question. We met and designed an experiment. We thought about problems like skill of tosser, variation in bottles, etc. We started with 32 bottles filled to varying levels. During 20 minutes of class, 32 students flipped bottles 4,220 times. We the all filled in our data on a Google Sheet.


I meet again next week with the small group that had the idea. I think they want to produce something for school news. Did we answer the question about how much water to put in the bottle?

Check out the graph of their data.


The Paper Helicopter is a similar exercise in experimental design. These activities come from the same template. If we understand that template, we can swap lots of different questions into the experiment, including those that seem most interesting to students in this moment.

We can teach students how to use mathematical tools to answer questions that interest them. We can also assign detentions. If there’s any middle ground, I’m not seeing it on Twitter right now.

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BTW. Here’s a Desmos activity you can use to facilitate data collection in your class. Your students add their data on the first screen. Then they see the sum of their class’s data on the second screen.

#BottleFlipping & the Lessons You Throw Back

I’m sorry. I went looking for a lesson and couldn’t find it.

Relevant background information:

Last spring, 18-year-old Mike Senatore, in a display of infinite swagger, flipped a bottle and landed it perfectly on its end. In front of his whole school. In one try.


That thirty-second video has six million views at the time of this writing. Bottle flipping now has the sort of cultural ubiquity that can drive even the most stoic teacher a little bit insane.

Some of my favorite math educators suggested that we turn those water bottles into a math lesson instead of confiscating them.

I was game. Coming up with a math task about bottle flipping should be easy, right? Watch:

Marta flipped x2 + 6x + 8 bottles in x + 4 minutes. At what rate is she flipping bottles?

Obviously unsatisfactory, right? But what would satisfy you. Try to define it. Denis Sheeran sees relevance in the bottle flipping but “relevance” is a term that’s really hard to define and even harder to design lessons around. If you turn your back on relevance for a second, it’ll turn into pseudocontext.

For me, at the end of this hypothetical lesson, I want students to feel more powerful, able to complete some task more efficiently or more accurately.

Ideally, that task would be bottle flipping. Ideally, students who had studied the math of bottle flipping would dazzle their friends who hadn’t. I don’t think that’s going to happen here.

But what if the task wasn’t bottle flipping (where math won’t help) rather predicting the outcome of bottle flipping (where math might). You can see this same approach in Will It Hit the Hoop?

The quadratic formula grants you no extra power when you’re in mid-air with the basketball. But when you’re trying to predict whether or not a ball will go in, that’s where math gives you power.


Act One

So in the same vein as that basketball task, here are four bottle flips from yours truly. At least one lands. At least one doesn’t. Each flip cuts off early and invites students to predict how will it land?

Act Two

Okay. Here’s a coordinate plane on top of each flip.

If you’ve been around this blog for even a day, you know what’s coming up: we’re going to show which flips landed and which flips didn’t. Ideally, the math students learn in the second act will enable them to make more confident and more accurate predictions than they made in the first act.

But what is that math?

I asked that question of Jason Merrill, one of the many smart people I work with at Desmos. I won’t quote his full response, but I’ll say that it included phrases like “cycloid type thing” and “contact angle parameter space,” none of which fit neatly in any K-12 scope and sequence that I know. He was nice enough to create this simulator, which has been well-received online, though even the simulator had to be simplified. It illustrates baton flipping, not bottle flipping

Act Three

Here is the result of those bottle flips. For good measure, here’s a bottle flip from the perspective of the bottle.


I’m obviously lost.

Here’s a link to the entire multimedia package. Have at it. If you have a great idea for how we can resurrect this, let me know. I’m game to do some video editing on your behalf.

But when it comes to bottle flipping, if “math” is the answer, I’m not sure what the question is. Please help me out. What is the lesson plan? How will students experience math as power, rather than punishment.

Sure, it’s probably a bad idea to destroy the bottles. But it’s possible we shouldn’t turn them into a math lesson either. Maybe bottle flipping is the kind of silly fun that should stay silly.

2016 Oct 7. Okay: I was wrong about #bottleflipping. A bunch of commenters came up with a great idea.

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Elizabeth Raskin:

I see a couple students playing the game during some down time and my immediate reaction is, “There’s gotta be some great math in there!” One of the boys who was playing sees my eyes light up. He looks at me in fear and says, “Mrs. Raskin. Please. I know what you’re thinking. Please don’t mathify our game. Let us just have this one thing we don’t have to math.”

Mr K:

I suspect I should put as much effort into making this teachable as I would for dabbing.

Meaghan found a nice angle in on bottle flipping, along with several other commenters:

It would be neat if you could spend a, for example, physics class period talking about experimental design (for fill ratio questions or probability questions) and collecting the data, and then troop right over to math class with your data to figure out how to interpret it.

Paul Jorgens has the data:

It started with an argument in class last week with the optimal amount of water in the bottle. Should it be 1/4 filled? 1/3? Just below 1/2? I told the group that we could use our extra period to try to answer the question. We met and designed an experiment. Thought about problems like skill of tosser, variation in bottles, etc. We started with 32 bottles filled to varying levels. During class over 20 minutes 32 students flipped bottles 4,220 times.

Ten Lessons from Ten Years of Blogging

One final indulgence for my blog’s tenth birthday: a list of ten lessons I’ve learned from ten years of blogging.

Figure out why you’re blogging. I started blogging ten years ago because writing helps me think and I needed some public pressure to think through my lessons at the end of the school day. Nowadays I blog because blogging makes me curiouser and wiser. I don’t want to say there are bad reasons to blog, but if you’re blogging first and foremost for fame, fortune, or readers, you’re going to feel very fried very quickly.

Find your cohort. Then encourage each other relentlessly. Ten years ago, my cohort probably included more administrators and English teachers than math teachers. The pool of edubloggers was so small we all followed each other, encouraged each other, and griped at each other. Find people who started blogging around the same time you did. For many people, your blogging and tweeting cohort will be the faculty lounge you’ve always needed and never had.

Be careful with auto-generated #content. For a long time people used plugins that would algorithmically attach a stock photo or a set of related links to your posts. Those have fallen somewhat out of favor, which is a positive development. If your goal for blogging is to develop your ideas or create a community, there just aren’t many shortcuts. Do the work.

Be the blogger you’d want to read. Figure out what you like about writers you read. As you work to develop your own style and voice, borrow theirs for awhile. Me, I like short sentences and clippy paragraphs. I like a mix of confidence and humility – someone who has strong opinions but holds them loosely. I like people who don’t take themselves too seriously. I try to write a blog I’d like to read.

Be nice. No nicer. No, dude, you think you’re being nice but you’re still really crabby. It took me awhile to realize there were, like, actual people behind the screen names and web addresses. I still struggle to criticize ideas online in ways that don’t bum people out. Related: punch up or don’t punch at all.

Figure out what blogging measures in your life. If you find yourself not blogging after a good run of blogging, that may just mean you don’t have the time for it. But in my case I figured out that it meant I wasn’t learning enough. Lately it means I need to get into a classroom or I need to do some math. That’s valuable self-knowledge.

Tend your comments. I delete spam quickly. I delete abusive comments. Occasionally, I email people privately to let them know they need to be nicer. If someone has a typo or an unclosed HTML tag or a link that didn’t get formatted properly, I’ll often fix those. Delete comments that don’t add value or propel conversation – even complimentary ones! If someone posts something positive but unconstructive like “Agreed!” I’ll often email a quick thanks and then delete the comment. People will rise to whatever bar you set, so set a high one.

Learn from your readers. A healthy comments section is like a really smart extra brain you carry around all the time and can consult whenever you want. Also, when people care about you and know what you care about, they’ll send you articles and ideas and links they think will interest you. That’s crazy. It’s better than any existing recommendation engine. The brain you carry around with you spontaneously generates knowledge for the brain you keep in your head.

Amplify your readers. I pull interesting comments up into the body of the post itself and let people know I’ve done that. I try to do that quickly, before the post gets emailed the next day, so email readers understand how much I value my commenters and can benefit from their thoughts too. This process creates a bunch of interesting and virtuous cycles. One is that I get more (and more useful) comments the more people know I’m paying attention to them. Another is that the next generation of interesting math education bloggers is in your comments right now. So amplify them. Embolden them to set up their own project. (See also: Ten Years of Blog Comments.)

Turn learning into more learning. If you do all of this and you do it regularly, my guess is you’re going to get offered some interesting opportunities. For me, I was offered chances to study with great researchers, to design curriculum with great designers, and to work with great teachers all around the world. I went into all of those opportunities thinking, “What will I find here that I can share with the folks back at the blog?” Again, not for fame, fortune, or readers. But because I knew you’d all make me curious and wiser.

Related, but not algorithmically generated:

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Michael Pershan:

The advice I’d give others about comments is simply to ask for comments when you want them. The way blogs work in 2016, you probably don’t have very many people reading you via RSS and not so many people regularly checking your comments sections. You are probably connected to other educators on social media, though these people might not know that you want feedback on your ideas. If you invite feedback, though, you’ll get more of it. That’s my advice.

Ten Years of Blog Comments

My blog turned ten years old this month so you’ll have to allow me a couple of indulgences.

First, I set myself up with a new blog theme. (If you’re reading this via email or an RSS reader, you’ll have to click through to check it out.)

Second, rather than reflect on ten years of my posts, I wanted to reflect on ten years of your comments. Over the last ten years, 4,600 people have written 20,000 comments on this blog, spanning two million words, the very first of which was written by Chris Lehmann.

My goal in blogging is to become curiouser and wiser with every post. Some of that happens in the post itself – through research, analysis, writing, etc – but so much of it happens in the comments.

To offer one current example, I posted Cathy Yenca’s method for teaching zero exponents last week. Forty comments later, my commenters offered two more methods for teaching them and helped me see how all three methods are related. I’m curiouser and wiser now than I was forty comments ago. That happened because of all of you and I wanted to thank a few you of you personally.

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For example, here are the ten people who commented most often in every year that I’ve blogged.

1Todd Seal84
3Jason Dyer74
4Jason Dyer53
5Bowen Kerins50
6l hodge72
7Kevin Hall46
8Kevin Hall39
9Ken Tilton49
10Paul Hartzer42

Longest Investment in My Work

And these are the ten people whose comments have helped shape my work for the longest span of time – from their first comment to their last.

1Karl Fisch9.2
2Tom Hoffman8.5
3Kate Nowak8.5
4Ian H.8.2
5Sam Shah8.2
7John Pederson7.8
8Michael Paul Goldenberg7.8
10Michael Serra7.6

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In 2011, I started to understand the gift of an active comments section, and how that gift needed encouragement and tending. So I began to add particularly helpful comments to the body of the post itself in a “Featured Comments” section. I made sure my commenters knew they had been promoted, hoping the endorsement would encourage them to continue bringing that kind of value.

These are the twenty people whose comments have been featured two or more times since 2011.

NameFeatured Comments
Bowen Kerins6
Dan Anderson3
Michael Pershan3
Barry Smith2
Bruce James2
William Carey2
Tom Woodward2
l hodge2
Larry Copes2
David Wees2
Laura Hawkins2
Jason Dyer2
Jason Buell2
Kate Nowak2
Michael Serra2
Nathan Kraft2
Ryan Brown2
Scott Farrar2

I sent a personal note of thanks to everybody mentioned in this post. Each person has made a significant donation of time, words, and insight to the project of making me curiouser and wiser.

Whenever people ask me how I got wherever it is I am right now, I always tell them about you, about how my ideas and thinking developed twice as fast as they had any right to. And I attribute that difference entirely to your time, words, and insight.

Wherever it is I’m going, I intend to get there exactly the same way.

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Congrats and well done! I think I remember that day back in 2007. I got to work, threw in a Nelly CD, fired up my Netscape browser and made my comment. Incidentally I drove the same Toyota Camry that I still drive to work. Later on I think I went home and watched Lost and then read about #hashtags

Collective Effervescence Is the Cost of Personalized Learning

Cross-posted from the Desmos blog. I’m happy enough with this post to re-broadcast it here. The Desmos blog doesn’t have comments, also, which makes this a better forum for you to tell me if I’m wrong.


We’re proud to debut our free Classroom Conversation Toolset, which has been the labor of our last three months. You can pause your students’ work. You can anonymize your students’ names. You can restrict the pace of your students through the activity. We believe there are productive and counterproductive ways to use these tools, so let us explain why we built them.

First, the edtech community is extremely excited about personalized learning – students learning at their own pace, uninhibited by their teacher or classmates. Our Activity Builder shares some of that enthusiasm but not all. Until last week, students could click through an activity from the first screen to the last, inhibited by nothing and nobody.

But the cost of personalized learning is often a silent classroom. In the worst-case scenario, you’ll walk into a classroom and see students wearing headphones, plugged into computers, watching videos or clicking multiple choice questions with just enough interest to keep their eyes open. But even when the activities are more interesting and cognitively demanding than video-watching and multiple choice question-clicking, there is still an important cost. You lose collective effervescence.

Collective effervescence is a term that calls to mind the bubbles in fizzy liquid. It’s a term from Émile Durkheim used to describe a particular force that knits social groups together. Collective effervescence explains why you still attend church even though the sermons are online, why you still attend sporting events even though they’re broadcast in much higher quality with much more comfortable seats from your living room. Collective effervescence explains why we still go to movie theaters; laughing, crying, or screaming in a room full of people is more satisfying than laughing, crying, or screaming alone.

An illustrative anecdote. We were testing these features in classes last week. We watched a teacher – Lieva Whitbeck in San Francisco – elicit a manic cheer from a class of ninth-graders simply by revealing the graph of a line. She brought her class together and asked them to predict what they’d see when she turned on the graph. They buzzed for a moment together, predicted a line, and then she gave the crowd what they came for.

She brought them together. She brought back the kids who were a bit ahead and she brought forward the kids who were a bit behind. She de-personalized the learning so she could socialize it. Because arguments are best with other people. Because the negotiation of ideas is most effective when you’re negotiating with somebody. And because collective effervescence is impossible to experience alone.

So these tools could very easily have been called our Classroom Management Toolset. They are useful for managing a class, for pausing the work so you can issue a new prompt or so you can redirect your class. But we didn’t build them for those purposes. We built them to restore what we feel the personalized-learning moment has missed. We built them for conversation and collective effervescence.

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