# What does “relatively uniform resonant frequency” mean?

In the book What If? from Randall Munroe, the author writes:

Q: Assuming a relatively uniform resonant frequency in a passenger jet, how many cats, meowing at what resonant frequency of said jet, would be required to "bring it down"?

I'm unable to google out any usage of "uniform resonant frequency" or even "relatively uniform resonant frequency" at all. I do meet "uniform resonance", but the results are all papers, which assuming that I have understood the word already. From my understanding, for every object there is only one resonance.

I think for a resembled object like a jet, each part has a different resonance, and if all of them is plotted, we can see if they are relatively uniform or not. The mechanical resonance does mention about airplanes, but I'm not sure this is the case.

So what does it mean?

• A related issue in aircraft is "flutter", where a control surface may flap in the breeze so forcefully as to damage the structure. Believe me, they've engineered vibration problems to death. There is no frequency you can blast a plane with to make it resonate to breakup. – Mike Dunlavey Feb 28 '17 at 21:06
• -1. This is not a difficulty with a concept of physics, it is a difficulty with communication and language because of a poorly-described situation. – sammy gerbil Mar 1 '17 at 3:52

It's exactly what you postulate it is -- a jet is composed of thousands (probably millions) of different parts, each of which would have its own frequency that induces the largest vibrations.

In order to make the problem tractable, the author had to make an assumption. The assumption made is that all of the parts have a roughly equivalent natural frequency, which the author chose to call "relatively uniform." The uniform means all equal, relatively means to within a close enough approximation. This means there is only one resonant frequency for the aircraft.

It is not a technical term. It's a plain-English term. And that's likely why you aren't able to search for precise meanings. But, the plain-English definitions are what makes the What-If series so charming and approachable.

• @Countto10 Without reading the book, I'd say it is. I mean, there's a lot of ways vibration could make an airplane fall apart right? Although usually it is related to wings falling off. At the end of the day, this isn't really a physics/science question and is just an English question so I wouldn't get too worked up about it. We're both saying the same thing (assuming one frequency despite there being many parts) in different ways. I don't say what one does with that frequency, while you offer a possible use. – tpg2114 Feb 28 '17 at 18:34
• it's hard to know if he's using plain English or not. I'm not a native English speaker – Ooker Feb 28 '17 at 18:38
• @Ooker In Munroe's work, it's pretty safe to assume he is always using plain-English unless there is a citation or definition immediately following the term. At least from what I've read from the online series -- I don't have the books. But that is generally his approach to technical content -- don't use technical words. – tpg2114 Feb 28 '17 at 18:43
• Do you think this question off-topic here? Maybe it should be migrated to English Language & Usage. Anyway, in many cases I see that the word in doubt is actually a term. – Ooker Feb 28 '17 at 18:54
• @Ooker Nah, I think it's okay here. I wouldn't worry about it unless people start voting to close/migrate. – tpg2114 Feb 28 '17 at 18:59

It means, AFAIK, you assign an overall frequency that causes the fuselage of the plane to suffer from stresses high enough to start a crack and lead to decompression. You base it around something you do know, the frequency of a cat's mewing, which I am sure is on the net. Then find how out how aluminium resonates as a tube.

That's how I would deal with it