Mathematician Calculates Rotational Speed of Fidget Spinner in Fidgets Per Second

iStock // fullempty
iStock // fullempty

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.

Can You Solve the Arithmetic Problem That's Stumping the Internet?

iStock
iStock

How much do you remember about arithmetic? This math problem spotted by Pop Sugar will put your knowledge of high school-level math to the test.

According to YouTube channel MindYourDecisions, the problem (9 - 3 ÷ 1/3 + 1) went viral in Japan after a claim was made that only 60 percent of 20-year-olds could get the correct answer.

Inputting this problem into a calculator won’t work—it will interpret the division incorrectly—so you’ll have to solve it the old-fashioned way to get the right answer. The answer may seem obvious to those who remember to “Please Excuse My Dear Aunt Sally” (a mnemonic device for PEMDAS, the order of operations).

Since there are no parentheses, exponents, or multiplication signs in this equation, the first part you’d tackle is division (3 ÷ 1/3). You should end up with 9, which will bring you to 9-9+1. Next up in the order of operations are addition and subtraction, which are performed from left to right. That should bring you to 0+1, and finally, a grand total of 1.

Did you get it? Common mistakes may lead you to 3, 7, 9, or -1, but try it again with Aunt Sally in mind and you should get the right answer.

To see more math problems like these, check out MindYourDecisions’s YouTube channel.

[h/t Pop Sugar]

See the World's Only Edible Bioluminescent Species

Fishermen trawl a net containing a large number of glowing firefly squid in central Japan.
Fishermen trawl a net containing a large number of glowing firefly squid in central Japan.
NORIAKI SASAKI/AFP/Getty Images

The firefly squid, or Watasenia scintillans, is the only commonly edible bioluminescent creature in the world. In Japan, the species is famous for the light show it puts on along the coast when it spawns each spring. That's when the fishermen of Toyama Bay, in central Japan, go out in the dead of night to harvest the squid by the bucketful. The fruits of their labors end up salted, grilled, boiled, or served raw in restaurants around the country. You can learn more about the firefly squid, and their harvest, in the video from Great Big Story below:

SECTIONS

arrow
LIVE SMARTER
More from mental floss studios