[PDF Distribution] Tsukiyumi Note #008 Flying Squid | From the Edo Sky to a Journey of Science and History

Why were old kites called "squid"?
What is the difference between an octopus (8 legs) and a squid (10 legs)?
How can a kite catch the wind and float in the sky?

Happy New Year. A new year has begun.

Tsuki: "I don't really mind not going anywhere for New Year's, but I have to go out if I want to get my New Year's money."
Mom: "Obviously. For Halloween and New Year's, you have to go out to get things; that's the rule."
Tsuki: "It would be nice if they could just deposit it via LINE."
Mom: "You're a million years too early to be trying to earn money the easy way!"

Even though the calendar alignment is good this year, we are staying home. Did everyone have a fun end-of-year and New Year holiday?

The Tsukiyumi Note, which I started at the end of the year, has reached #008. I would like to continue at a pace of 1-2 posts per week this year as well.
And, while I usually introduce a digest version, since it is New Year's, I am leaving the full version PDF here as is. I would be happy if you could use it to kill some time during the holidays. (The PDF is at the end of the article.)

Let's have a healthy, cheerful, and good year in 2026 as well.
I look forward to your continued support this year.

Once upon a time, "squid" swam in the Japanese sky. This refers to the "kite" (tako), a seasonal tradition of the New Year. In the Edo period, this pastime was called "ikanobori" (squid climbing). With a square head and long legs, its appearance was exactly like a squid. However, it became so popular that adults started fighting and people were getting injured, so the shogunate actually issued a "ban on squid climbing." The commoners who still wanted to play thought, "This isn't a squid, it's an octopus (tako)!" This humorous bit of sophistry took hold, and it is said that it came to be called "tako" (octopus), especially in the Kanto region. The sound of "tako" also carries the wish for "takou" (much happiness).

Not the "octopus" in the sky, but the "octopus" in the sea, as well as the "squid." Biologically, they are members of the group called "cephalopods." Octopuses have 8 arms and squids have 10, and both possess high intelligence. In particular, the "mantle" (ear-like fins) that allows squids to glide through the sea has a shape that makes sense from a fluid dynamics perspective.

Now, why does a kite made of paper rise high into the sky against gravity? There is a scientific force at work called "lift." The key is the "angle." By tilting the kite slightly against the wind, the force of the wind is converted into an upward force. This is the same principle by which airplanes fly. People in the Edo period discovered this scientific law through experience and enjoyed it.

Let's try it
● Work 1: "Palm Airplane" Experiment
Hold your palm horizontally facing the wind from a fan or natural wind. From there, try raising the front part of your palm little by little to create an angle (angle of attack). Feel at what angle your hand is lifted upward most strongly. You can also experience how the force weakens if you tilt it too much. This is the sensation of "lift" that makes airplanes and kites float.

● Work 2: Seeing "Symmetry" with Paper Cutting
Prepare some origami paper. For the octopus shape, if you fold the paper into a square twice, then into a triangle, cut a pattern from the center, and unfold it, it becomes "rotationally symmetric" (the shape is the same even when rotated). For the squid shape, if you fold it in half vertically just once, cut out half the shape of a squid, and unfold it, it becomes "line symmetric" (the left and right sides are the same). Compare the shapes you made and think about which one looks more stable or seems easier to move.

● Work 3: Essay "On Invisible Threads"
A kite is connected by a string, but there are also "things that are invisible but connected" in our daily lives. It might be relatives living far away, old friends, or infrastructure like electricity or the internet. Write a short essay imagining when you felt that connection and what would happen if it were cut.

The above is an excerpt from the teaching materials I create for home study with my son.
[Teaching Material Content] Flying Squid
・Historical background of the names for kite (tako) and squid
・Mechanism of how lift is generated (angle of attack)
・Body structure of octopuses and squids (rotational symmetry and line symmetry)
・Relationship between Japanese ocean currents and the fishing industry
・How living creatures are perceived in different cultures
・Connection between oneself and society (essay)

▼ Download the PDF here (free)
(This is the full version of the teaching material I create for home study with my son.)