Sharon Cohen, the brand manager at Orbeez, checks in on the last post:

The disparity (150/100) is based on the fact that growth depends on ionic content of the water–the purer the water the larger they grow. The very same Orbeez wll grow to a different size depending on the water purity. The number we chose ended up being a marketing decision (100 is a powerful figure) but we should have been consistent. It’s impossible to choose one accurate number.

BTW: Sharon Cohen sent along Orbeez’ internal measurements of expansion given different water sources.

This one is about a year old. It’s short and simple. As I recall, I used it for an opener problem and nothing more. In my development as a math teacher and curriculum developer, though, it has a lot of sentimental significance. In Leslie Knope’s Love Life, I wrote about my goal to draw inspiration closer to action through practice, practice, practice, and this is the result.

I was driving along, checking Maps on my iPhone for directions, and found it interesting how the blue tracking orb moves faster when you’re zoomed in close to the map and slower when you’re zoomed out. Reflexively, I turned it into a question: “how fast is the car going, given this particular orb?” Then I tweaked it: “Do we arrest this person for speeding?” (Crime doesn’t pay, but it’s more interesting to my students.) Then, just as reflexively, I knew the image I needed to create.

iPad – No Timer from Dan Meyer on Vimeo.

Such a simple thing, but it was one of the most satisfying moments of my professional life.

The Goods

The problem archive, including:

1. the video with the timer,
2. the video without the timer,
3. a photo of a speed sign at that intersection in Compton,

Just to be totally clear, I wouldn’t bring this video inside fifty feet of a classroom. I’m not recommending you use this video in a classroom. I’m recommending that when you see math in the world around you that you get in the practice of doing something about it – especially, that you turn it into a question.

Don’t know how to do the black box and the censor beep? Just pause the video right before she answers her own question. Point being, the more you habituate this practice – even on lessons like this one that won’t go anywhere – the more often you’ll catch these moments.

Here’s the answer:

The Goods

The problem archive, including:

1. the question video,
2. the answer video,

Don’t do it, seriously.

Sorry to be all post-y today but reader Ryan Bavetta sent in a hot tip and I had to jump on it before Drudge did. Here’s Obama delivering his State of the Union address. Ryan says, “I don’t think they got the sizes of the circles right.”

So I go all Woodward and Bernstein with my compass and protractor. I measure off the diameters.

The ratio of the diameters is 2.45, which means the ratio of the areas is going to be (2.45)^2 or 6.00. But the ratio of America’s GDP to China’s GDP (14.6T/5.7T) is only 2.56! The US circle is too big! What’s the progressive propaganda machine trying to sell us here?!

Here’s how it should have looked:

For Classroom Use

I think you have to get rid of one of the quantities, ask the students to determine it, show them the full SOTU screenshot, and then encourage them to marvel at the difference. You can give them Obama’s circle and ask them to tell you what that should make the GDP.

Or you can give them the GDP and ask what that should make the circle.

I don’t know how to get excited about the difference when Jon Stewart’s probably trying to call my booking agent right now.

The Goods

The problem archive, including:

1. the original image,
2. the image without the GDP,
3. the image without the circle,
4. video from the speech itself,
5. an extension problem.

2011 Feb 16: Updated to add higher-resolution images, video from the speech itself, and an extension problem.

Also: I Need To Get A Collection Of These Going