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Swinging an umbrella while walking has same force as a piano, Tokyo government claims

Master Blaster Mar 28, 2025
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Watch where you’re pointing that thing!

When it rains it pours in Japan, so you’d be hard-pressed to find anyone not walking around with an umbrella when rain clouds gather. However, when the rain doesn’t fall these things can be a real pain to haul around due to their awkwardly elongated shape. A lot of people find that holding them sideways is the least burdensome, but the Tokyo Metropolitan Government is warning against that for the sake of public safety.

▼ By sideways, they mean in such a way that the pointy end juts straight out behind or in front of the carrier. Note that his photo was taken in a controlled environment with no risk to the public.

Photo ©SoraNews24

Just how dangerous is walking with a sideways umbrella? Well, according to the government’s own study, the impact of an umbrella swung this way is equivalent to getting hit with a baby grand piano.

▼ Imagine you were hit by one of these, it’s easy if you try.

Image: Wikipedia / Lisa

They determined this by fixing an umbrella sideways to a pendulum and letting it swing down from a 45-degree angle. This was measured to have a 240-kilogram-force impact. Government officials added that this piano-equivalent force was also concentrated in the small tip of parasols, making them even more dangerous.

It’s a startling declaration, and readers of the news online left comments of awe and fear at these once seemingly harmless rain-blockers.

“Umbrellas are deadly weapons.”
“I wish people would stop swinging them while walking.”
“This is way more important than wearing backpacks on your front.”
“I hope this will reduce the number of people holding umbrellas sideways.”
“It’s scary to think of someone running up the stairs with an umbrella like that and hitting the person behind them.”
“Now, that’s what I call a street piano!”
“Umbrellas should be banned.”

I agree that I never knew an umbrella could be so powerful, especially since I don’t think I could even intentionally attack someone with one and hit them as hard as a piano. I guess the best fighting tactic is to just power walk away from my opponent and swing my arms a lot.

But before you start carrying around an umbrella for self-defense as well as staying dry, these results are a little misleading. First, it uses a unit known as “kilogram-force” rather than the standard Newtons to measure force. “Kilogram-force” just refers to the force an object applies under gravity, i.e. its stationary weight.

This means that if I were hit in the hand by an umbrella swung with the force reported by the Tokyo government, it would be like having a piano gently placed on top of my hand, but only for that fraction of a second when the impact occurred. Granted, that’d still probably hurt quite a bit and could even break a bone when such a force is delivered through the small tip of an umbrella, but it’s still a far cry from actually being hit by a piano. That would require a lot more force.

To put it into more universal units, the government claims the swing of an umbrella would be in the neighborhood of 2,300 Newtons, roughly equivalent to a punch by a low-level but skilled boxer, a soccer ball kicked by a pro at full force, or a bump by a car going about 10 kilometers per hour (6 miles per hour). Honestly, I would not want to be on the receiving end of any of those things, so I’m not sure why they didn’t just go with those instead of the piano analogy.

▼ A blow from our amateur kickboxer Go Hatori might register in that range.

Photo ©SoraNews24

The other problem is that the research used a pendulum, which means the umbrella was fixed to a completely rigid arm and mercilessly followed a perfect arc to its target. That would maximize the force of impact for a worst-case scenario which is technically possible but very unlikely in real-life situations.

It’s hard to estimate the real-life force of such an impact given all the variables, but we can give it a rough shot. To do that we can take an average adult arm weight of around 3.5 kilograms and average umbrella weight of 0.7 kilograms, and estimate a normal walking arm swing to be about half the speed of an intentional punch by an average person, or about 2.5 meters per second. I’ll also assume an impact time of 0.1 seconds, which I think is too slow but I’ll use it just to err on the side of a harder hit. Putting that all together…

You probably can expect a jab from someone’s umbrella while walking to be realistically in the ballpark of 100 Newtons, which is like getting hit by a soccer ball kicked by a grade-schooler at full force or dropping a 1-liter (34-ounce) bottle of Grape Fanta on your foot. Those certainly suck too, but we’re way out of getting-hit-by-a-piano territory.

I don’t mean to diminish the core message of the Tokyo government. It just bothers me when misleading logic is used like that, even when well-intentioned, because it lowers the messenger’s credibility overall. I agree that umbrellas sticking out are annoying and personally, I think everyone should use their umbrellas like classy little canes when walking around. I love pretending I’m Mr. Peanut and you will too.

Source: TBS News Dig, Hachima Kiko
Featured image: Pakutaso
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