Q: Can resonance be used to destroy anything? Is the “brown note” possible?

Physicist: Nope!

“Resonance” is a “driven harmonic oscillation“, where the driving force pushes and pulls at, or near, the “resonant frequency” of whatever it is that doing the resonating.  There are two big issues involved with destroying stuff using sound, or gentle taps, or whatever you’re using to drive the motion.  The first is that nothing in the world “rings” perfectly, and the second is that every example of harmonic motion you’re likely to come across is actually an example of “damped harmonic motion”.

Here’s what “not ringing perfectly” means.  You can make anything bounce around and shake, but “harmonic motion” is something very specific.  Harmonic motion is a vibration that takes place at just one frequency.

Harmonic motion

Something that moves harmonically moves back and forth in a sine wave.  Maybe more or less spread out or taller than this, but always in exactly this shape.

When something is oscillating back and forth there has to be a “restoring force” to bring it back to center.  For a swinging pendulum that force is gravity, for a spring or a wine glass it’s the springiness of the material.  The one requirement for harmonic motion is that the restoring force is linear, and proportional to how much the object has been pushed from center.  For example, if you pull on a spring by a distance X and it pulls with a force F, then if you pull it twice as far, 2X, it will pull with twice the force, 2F.  This is the famous “Hooke’s law“: F = -kX.  The negative here means that the force points in the opposite direction of the displacement, so if a pendulum has swung to the right, then gravity is pulling it to the left.

When you change things by just a tiny bit the response is almost always linear.  Or at least very nearly linear.  If this weren’t the case, then physicists would barely be capable of doing any calculations at all.  This is called a “first order approximation” or “linearization”, and it’s really just the statement that things (in a mathematical sense) are smooth.


A typical force response for a spring.  If you don’t stretch it too far it reacts linearly (straight line), but if you stretch it too far then it doesn’t (and eventually gets turned into a straight wire or breaks).

Most physical systems have the “linear on a small scale” property.  It’s just a question of when it breaks down.  This is why clock pendulums don’t swing very far, for example.

So this is the first big problem; if you push something hard enough, or if the oscillation gets too large, then the restoring force won’t be linear.  As a result the system starts to lose all of the nice properties that make it a harmonic oscillator.  One way for this to happen is for the object to break (huzzah!), but most of the time the oscillation frequency starts getting wonky, the wave stops being pretty (not just one frequency), and trying to induce resonance just sorta stops working.

The second big problem is dampening.  Nothing’s perfect so over time every oscillator loses energy.  Pluck a guitar string, and it’ll eventually go mute.  Stop pushing a kid on a swing, and they’ll eventually just sit there.  And maybe get hungry.

Damped harmonic oscillation looks like this.

Damped harmonic oscillation looks like this.

When you try to make something resonate you’re adding up a bunch of these waves (one for every time you “push the swing”), but because of dampening the waves from earlier don’t add as much as the waves from later.  Even if the system is still pretty linear, this puts a cap on how big an oscillation you can get for a given amount of pushing.

So, just to make sure the point on this is too fine, even if the frequency is dialed in perfectly, most things can not be destroyed by resonance.

If the dampening is bad enough, then instead of resonating at all the object will just “ooze” back to where it started.  When things are “over-damped” patience completely stops being a virtue and you really need to get all of the energy in place all at once.  For example, if you’re using sound you’d need to replace the speaker or your voice with a bomb or a hammer.

The “brown note” is a sound that supposedly resonates intestines and makes a mess.  However, there are issues.  Entrails don’t ring like bells, they flop like meat.  Even if you’re careful to stay in the “linear regime” (very, very small forces and oscillations), you’ll find that meat is usually critically damped, although not always.

There are better ways to induce trou dropping: laxatives, roller-coasters, away-toilet situations, etc.

While it is true that the (American) military has spent some money looking into the brown note (lots of people have), it’s also true that they’ve spent some money looking into almost everything.  Statistically speaking, you can’t spend $680,000,000,000 without buying something useless.

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30 Responses to Q: Can resonance be used to destroy anything? Is the “brown note” possible?

  1. Scott says:

    This is a case of asking the wrong person. Ask a Physicist how to solve constipation, and you get a long and convoluted answer involving harmonics, the military’s budget and “brown notes”. On the other hand, if you ask a Mathematician to solve constipation, he quickly works it out with a pencil.

  2. george d conger says:

    Just read Can Resonance destroy………
    Then, can you tell me why a photon from a far off galaxy doesn’t lose frequency (energy) while on it’s way to our telescopes and become red-shifted naturally.
    I am not, obviously, a Big Banger.

  3. kopernik says:

    On Resonance –
    An example of a standing wave can be found in the jets of some galactic nuclei. See M87. ‘Globes and clots’ that do not seem to move very fast within the jets are resonant waves (my opinion).
    These probably have an acoustic component. K

  4. The Physicist The Physicist says:

    Photons aren’t “mechanical” the way springs are. While they do have frequencies, they aren’t harmonic oscillators. That said, over large enough time scales they do slowly red shift, however the cause is different from friction (which is how most oscillators loss energy).

  5. Steve says:

    Tacoma Narrows Bridge Collapse
    Your “Nope” is contradicted by your “huzzah!” When the response becomes nonlinear it can mean that the proper function of what is vibrating has been lost, and that amounts to destruction. (Chattering windshield wiper blades do a bad job of clearing the windshield, and such chatter is a tame destruction that has a lot in common with what caused the bridge collapse.)

    The Tacoma Narrows Bridge was not set in motion by a rotating eccentric mass, or a dog that mistook it for the Brooklyn bridge, but vortices shed by the structure in the wind were in tune with one or more of it’s natural frequencies. This kind of self-excited vibration is a problem recognized by engineers, if not by physicists.

  6. Flavian Popa says:

    Amazing..A myth states that’s how Atlantis was submerged, they got so technologically advanced they really started creating an Earton, a wave that in their not so humble opinion would have “created” a planet..the result, Atlantis got underwater pretty bad…well, just a myth..or maybe not

  7. Elaine Puricelli says:

    Hmmm…. I always wondered if one could place a tuning fork (o.k. a very large one) at a hillside and strike the tuning fork to it’s perfect frequency or tone.
    Just to see if it makes any difference in the hillside (collapse or even just a wobble).
    The same would apply to a bridge or overpass or road crossing a hilltop.
    With the perfect resonant tone imparted……could there be damage?
    Always wanted to try this.

  8. The Physicist The Physicist says:

    I should have made a bigger distinction between “anything” and “everything”. There are things that can be destroyed through some form of resonance (including the ill-fated Tacoma Narrows). So there are some things that can be broken, but not every thing.
    The point of the post was that the vast majority of physical objects that you’re likely to come across can’t maintain a nice resonant frequency up to the scale at which that object would break.

  9. Elaine Puricelli says:

    Are you referring to the coefficient of friction exerting it’s “stopping force” on objects
    when you say “…can’t maintain a nice resonant frequency…”
    There’s of course the example of the shattering crystal wine glass when a
    certain pitch (frequency) is achieved.
    I would like to conduct an experiment where a hillside overpass (road is paved over
    a hillside) could be monitored to see what frequency or amount of resonance is
    achieved by vehicles driving across. I still like my “big tuning fork” idea on
    a hillside to see is physical changes can occur when increasing a frequency.

  10. Zlatko Bolterstein says:

    Bridges can be destroyed by resonance, for example.

    Something that is known by the military for quite some time – it is standard procedure with military marches should the unit come across a bridge it will be ordered not to cross it in marching step but in unsynchronized step (out of cadence).


  11. Elaine Puricelli says:

    I knew about “breaking cadence” from my Army days.
    So what about effecting damage to mountains by resonant frequency?

  12. The Physicist The Physicist says:

    Our mountains are safe from this particular threat. You were in the army, Elaine?

  13. Elaine Puricelli says:

    Yes, I was a reservist (back in the day) called up to active
    duty during Desert Storm. I went inactive after I returned to
    reserve status. Army nurse corps. I left as a 1st lieutenant.
    I probably would’ve stayed in reserve status after I returned
    but I wanted to move on. Weird timing. I joined the reserves
    in ’89 and the call-up was Dec. 1990. I was allowed to go to
    inactive ready reserve status because after Desert Storm my unit
    was dissolved. So anyone wishing to remain a reservist from that
    unit had to drive 100 miles to join another reserve unit. I didn’t
    want to be career Army anyway.

  14. george says:

    Photons ARE mechanical in the sense that they follow natural physical laws.
    They are dependable in that way.
    Photons from far space are red shifted because they have lost energy in route to us. unless of course, you are one of those Big Bangers.

  15. eric says:

    And and one point of that frequencies life it has had the potential to destroy.

  16. Johan says:

    There is a grain of truth about the “brown note” that is slightly more boring than the narrative presented by A and J, and it has nothing to do with resonance. infrasound can cause emotional distress, even if they’re not perceived as sound. For example, a house that was perceived by somebody to be haunted, ceased to be perceived as such after an old fan spewing out subsonic waves was disposed. Another consequence of this is that it’s a bad idea to live next to a busy road, even if leaded gas has been banned.

    Now, if you, say, interrogate a prisoner of war, perhaps by restrain their movement and abusing them verbally and/or physically, it might be that the added distress from a little bit of distress from infrasound is what it takes to tip the balance from “functioning sphincter” to “OH GOD I CAN’T TAKE THIS ANY MORE!”

  17. Erik E says:

    “Harmonic rock” derailments were common when I worked on the railroad before the widespread use of continuous welded rail. Standard thirty nine ft. rails could not be staggered in track on center, and trains were ordered not to maintain ” critical speed”; around 19 mph. if I recall.

  18. The Physicist The Physicist says:

    Holy crap that’s interesting!

  19. Elaine Puricelli says:

    So…The Tacoma Narrows bridge disaster’s “driving force” was the wind?
    Or the sum total of winds blowing into the bridge , a bridge that had no
    allowance for air currents? I’m remembering 1993 in my town when a tornado
    “danced” on a large cantilever bridge then sliced through a WalMart store without
    destroying much of anything else (including the cantilevered bridge) in it’s wake.

  20. Obedaea says:

    I think Mr Rife would disagree.

  21. Elaine Puricelli says:

    So…back to resonance. I’m seeing the answer to my question about taking down
    a mountain with the use of a large tuning force – large enough to emit a resonant
    energy that will make the mountain as vulnerable as a crystal glass in an opera house,
    but what about earthquakes? The area in Virginia where I live was the target of a 5.8 quake in 2011. There have been more rumblings since then just not 5.8 scale.
    Can the earthquake produce a resonant energy large enough to literally move a mountain (reduce to rubble) with its destructive force? Doesn’t every example of matter (o.k., a mountain is a pretty big chunk of matter) have it’s limit in the game of targeted resonant energy? Look at what I see as the fragile Natural Bridge in Virginia.
    Sure, it’s a large rockish mountain wherein a large slice was removed to form a natural bridge. I’ll bet that’s a good starting point to observe resonant energy’s destructive nature (theoretically of course).

  22. Elaine Puricelli says:

    Hmmm…. I’m surprised there’s no response to this resonant energy question.
    Perhaps I’m confusing everyone by equating an earthquake to resonant energy.
    O.k……forget the earthquake. We could potentially take down a mountain…o.k.,
    hillside (let’s start small) with a large tuning fork. Right? Again paralleling the
    hillside/mountain with a crystal glass in an opera house.
    I guess if that were true developers wouldn’t be using dynamite.
    But I like my idea anyway.

  23. Matthew says:

    This phenomenon draws me to think that the recent collapse of prophet TB Joshua’s church in Nigeria was as a result .A jet flying round the building four times leading to the sudden collapse of the building.Is there a way that could result in the collapse?

  24. Mike says:

    I’m wondering why the simple concept of resonant frequency be used to destroy a cancer cell?

  25. Ekayon says:

    I took this concept of material resonation a bit further and built something that can use sound to break stuff! first tests show it is possible to break a brick wall with sound. i did that with 4 speakers facing a single point 8 meters in front of them. then i used 4 different pure tones at exactly the same time randomly alternating them between the 4 speakers 64 times a second and in 64 different frequencies. And voila! the wall started to crack after a few seconds where the mortar is.

    (Sorry for my bad English)

  26. Hadi Jalloul says:

    I always wonder about total distruction through sound waves, but never knew it is too effective. I thought if a plane can be surrounded by many heavy speakers, that may emit sounds higher than the engines and but with the same frequency to be take a benifit from the engine noise. The plane can go at the speed of sound, this is possible these days having many military planes, and then activate the speakers, the sound must stack with its self due to its fast regeneration in the path of the plane, and then head forward to the target. The sound will become heavier and more distructive this way, and before hitting the target the speakers turn of and the plane changes track. The waves that will reach the target will reach with the same frequency, which will be devastating, and the target will blow up. It is as sending a reusable heavy missle, but much higher technological and can’t be stopped. Please reply here or send me an email telling me if this is possible or not. [email protected]

  27. George D Conger says:

    “Sound” is used in medicine to destroy (vaporize) unwanted tissue.

  28. luisa says:

    Not a comment, but I would like, if you please, to see how is calculated the level of oceans rise from the melting of the polar ice caps and icebergs on mountains caused by global warming. Thanks in advance.

  29. HDhedhu says:

    Can loud enough sound make building fall?

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