2025年12月2日 / Last updated : 2025年12月3日 桑子 研 Science

A Science Teacher’s Secret to Winning Daruma-Otoshi: Master It with Newtonian Physics!

I’m Ken Kuwako, your Science Trainer. Every day is an experiment.

The Daruma Otoshi is a traditional Japanese folk toy, beloved by many. But did you know that it’s also a surprisingly perfect teaching tool for demonstrating the Law of Inertia that you learn in science class?

While it’s often cited as a textbook example, surprisingly few students have actually played the game. Don’t underestimate this seemingly simple children’s game; the very essence of Newtonian mechanics is hidden within its structure. If you happen to have a Daruma Otoshi nearby, pick it up! Today, I’m going to reveal the “Daruma Otoshi Winning Strategy,” explained through the lens of physics.

Conquer the Physics! The Most Important Elements are “Speed” and “Friction”

First, stack them up neatly.

The most crucial thing for a successful Daruma Otoshi strike is to “swing through quickly and without hesitation.”

The key here is “frictional force.” The moment the hammer strikes the bottom piece, friction acts between that piece and the one stacked above it, trying to drag the upper piece down. However, the faster you strike, the less time friction has to act. As a result, the horizontal force applied to the upper pieces is minimized, and the force of “inertia”—the tendency to remain in place—wins out. The upper stack then falls cleanly straight down.

If you hesitate, or if the speed of your swing is too slow, the friction acts for too long, causing the upper pieces to tumble down with the one you struck. Gathering the courage to “strike hard and follow through” is physically the correct approach.

Is “Bigger” Easier? The Surprising Link Between Mass and Inertia

There is actually a surprising paradox in Daruma Otoshi: Larger and heavier sets are often easier to play than smaller, lighter ones. Conversely, tiny plastic sets can be difficult, requiring a professional level of precision.

Why is this? The rule at work here is that “greater mass means greater inertia (meaning it resists change in motion more).” Just as a heavy truck cannot stop suddenly, a heavy Daruma stack has a strong tendency to remain in its state of rest. Therefore, the greater weight (mass) compensates even for a slightly imperfect strike, making success more likely.

The Player Who Masters Balance Wins the Game

The next important factor is the direction of your strike. To prevent the overall balance (center of gravity) from collapsing, it’s generally best not to strike continuously from the same side. Instead, try alternating strikes from the left and right sides.

In a real game, the position of the center of gravity changes momentarily with every strike and shift. The advanced technique involves observing which way the stack is leaning and adjusting your strike direction to nudge the center of gravity back toward the middle.

The Biggest Challenge is the “Last Piece”

The most difficult phase of the game, from a physics perspective, actually occurs at the end. What happens when fewer pieces remain and there are fewer Daruma dolls stacked on top?

That’s right—the overall “mass” is reduced, which means the “inertia” becomes weaker. The upper section, which felt solid and stable due to its weight in the beginning, becomes very light toward the final piece, and even a slight impact can easily send it flying off. “The Daruma Otoshi is hardest at the end.” This is the fundamental truth taught by the laws of mass and inertia.

Even knowing the theory, putting it into practice can be tough! Watch me attempt the challenge in this video:

If you watch the video, you can see how the difficulty gradually increases (and the behavior becomes less stable) from the initial full stack to the final few pieces. I hope you all try this and feel the Law of Inertia with your fingertips.

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