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Mathematician Calculates Rotational Speed of Fidget Spinner in Fidgets Per Second

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How fast does a fidget spinner spin? It's a simple question with a simple answer, but a complex path to that answer. The issue lies in analyzing an extremely fast-moving object with simple tools, like a smartphone.

In the video below, mathematician Matt Parker turns to a spectrogram sound-analyzing app to solve this problem. Spectrograms are visual representations of sound, allowing the viewer to pick out certain frequencies within an audio clip and measure their intensity. By figuring out the sound the fidget spinner makes, Parker can sort out how many Hertz (cycles per second) the spinner is rotating at.

The first task is making the spinner itself stable, so it's easy to spin and becomes a reliable target for audio recording. Parker attaches the device to a drinking glass, and mounts the smartphone above it, with the microphone pointed at the edge of the spinner. Then by blowing the fidget spinner with compressed air, the mathemagic happens.

Parker calculates the absolute speed of the tips of the fidget spinner, as well as the speed of the spinner in revolutions per minute—the latter is roughly 3750 rpm! (For comparison, a typical car engine runs around 2000-3000 rpm when cruising.) The video is full of further analysis and methodology.

Tune in for some delightful applied mathematics...and be sure to wear your safety gear!

Incidentally, Parker used the SpectrumView app, though there are others like it. He also posted a screenshot of the spectrogram, as seen in the video, in case you want to test your own spinner.

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Watch This Robot Crack a Safe in 15 Minutes
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Wired, YouTube

When Nathan Seidle was gifted a locked safe with no combination from his wife, he did what any puzzlemaster—or, rather, what any engineer with a specific set of expertise in locks and robotics—would do: He built a robot to crack the safe. Seidle is the founder of SparkFun, an electronics manufacturer based in Denver, and this gift seemed like the perfect opportunity to put his professional knowledge to the test.

The process of building a safecracking robot involved a lot of coding and electronics, but it was the 3D printing, he said, that became the most important piece. Seidle estimated that it would take four months to have the robot test out different combinations, but with one major insight, he was able to shave off the bulk of this time: While taking a closer look at the combination dial indents, he realized that he could figure out the third digit of the combination by locating the skinniest indent. Thanks to this realization, he was soon able to trim down the number of possible combinations from a million to a thousand.

Watch the video from WIRED below to see Seidle's robot in action, which effectively whittled a four-month safecracking project down to an impressive 15-minute job.

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This Puzzling Math Brain Teaser Has a Simple Solution
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Fans of number-based brainteasers might find themselves pleasantly stumped by the following question, posed by TED-Ed’s Alex Gendler: Which sequence of integers comes next?

1, 11, 21, 1211, 111221, ?

Mathematicians may recognize this pattern as a specific type of number sequence—called a “look-and-say sequence"—that yields a distinct pattern. As for those who aren't number enthusiasts, they should try reading the numbers they see aloud (so that 1 becomes "one one," 11 is "two ones," 21 is "one two, one one,” and so on) to figure the answer.

Still can’t crack the code? Learn the surprisingly simple secret to solving the sequence by watching the video below.

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