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Hoofbeat
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Just been wondering :rolleyes: you know when a board-pen on a whiteboard screechs (sp?), or when you catch your fork on a plate and it makes that horrible sound how it literally hurts your head (I find my teeth feel funny?) is it because the frequency of that sound matches the natural frequency of say your teeth/ears and resonance is occuring?

I've been thinking about this for a while...any ideas?
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john !!
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Interesting! It would make sense if those noises (like scratching nails on a chalk board) had some resonance with sonething - lol I don't know how resonance with glass works, something to do with the frequency of the waves being the same length as the frequency of atomic vibrations so the atoms get pushed and pulled more and more until the bonds are broken and the glass smashes. Maybe the same happens with something in the body that makes it uncomfortable to listen to those noises...

I'll think about that more later, sounds like an interesting theory.
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elpaw
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you can get resonance in the body. i think the americans or soviets or someone were developing sound weapons to use in the cold war that would literraly smash someone to peices due to resonance, but it was too complicated because each person (let alone his individual body parts) has their own individual natural frequency
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Resonance
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Interesting thoughts, and since my name is Resonance I felt it was my duty to offer my own (though it's not your duty to read them!)

My little sister often shouts rather high-pitchedly, and when she reaches a certain pitch it hurts my head badly, and I thought that might be resonance.

In the same way, before my car was serviced, it used to make a horrible vibrating noise when it reached a certain number of revs. It would be most evident in first gear and really annoying. I think those revs were the natural frequency of some dodgy component.
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Hoofbeat
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(Original post by elpaw)
you can get resonance in the body. i think the americans or soviets or someone were developing sound weapons to use in the cold war that would literraly smash someone to pieces due to resonance, but it was too complicated because each person (let alone his individual body parts) has their own individual natural frequency
Yes, I too have heard about that. Just wondered whether these "horrible" noises were perhaps a slight example of resonance in the body. I'll see what my physics teacher thinks when I go back to school 2moz.
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JamesF
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(Original post by elpaw)
you can get resonance in the body. i think the americans or soviets or someone were developing sound weapons to use in the cold war that would literraly smash someone to peices due to resonance, but it was too complicated because each person (let alone his individual body parts) has their own individual natural frequency
Ive heard about that, I presumed they just used the resonant frequency of water since we are full of it. Geneva convention prevents it from being used anyway. Great idea tho, you dont have to worry about destroying buildings or anything.
I think that the whiteboard thing is like when you rub your finger around the top of a crystal glass, the atoms are pulled apart, then let go, so they vibrate.
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Jonatan
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(Original post by Hoofbeat)
Just been wondering :rolleyes: you know when a board-pen on a whiteboard screechs (sp?), or when you catch your fork on a plate and it makes that horrible sound how it literally hurts your head (I find my teeth feel funny?) is it because the frequency of that sound matches the natural frequency of say your teeth/ears and resonance is occuring?

I've been thinking about this for a while...any ideas?
No, the sound is uncomfortable because it is harmful to the ears. The sound you are reffering to is typically of high frequency containing lots of distortion and also has quite a great amplitude. This type of sound could damage your hearing (more specifically the cells to which teh flimmer hairs detecting the sound is atatched) if you were exposed to it for a long time.
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Hoofbeat
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(Original post by Jonatan)
No, the sound is uncomfortable because it is harmful to the ears. The sound you are reffering to is typically of high frequency containing lots of distortion and also has quite a great amplitude. This type of sound could damage your hearing (more specifically the cells to which teh flimmer hairs detecting the sound is atatched) if you were exposed to it for a long time.
Oh right. How come though sometimes it's by teeth that feel funny - especially when the fork makes a noise with the plate?
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davey_boy
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(Original post by elpaw)
you can get resonance in the body. i think the americans or soviets or someone were developing sound weapons to use in the cold war that would literraly smash someone to peices due to resonance, but it was too complicated because each person (let alone his individual body parts) has their own individual natural frequency

And interestingly someone showed some 'haunted' house had a corridoor where wind often blew down it at a certain velocity, creating standing waves at certain points in the corridoor and surrounding rooms. The wavelength of these standing waves was very close to the resonant frequency of the human eye. They concluded if your eyeball started resonating then you'd 'see' some very strange effects. Think it got published in nature about 3 years ago....
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JamesF
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(Original post by davey_boy)
And interestingly someone showed some 'haunted' house had a corridoor where wind often blew down it at a certain velocity, creating standing waves at certain points in the corridoor and surrounding rooms. The wavelength of these standing waves was very close to the resonant frequency of the human eye. They concluded if your eyeball started resonating then you'd 'see' some very strange effects. Think it got published in nature about 3 years ago....
Oh, yea, cars about 20 years ago used to vibrate at the same frequency, about 20 hz i think, and the effect is to make you seem drunk, or like u've taken some kind of drug. They had to fix it cos it was causing accidents.

Also, some ancient civilisations used this same idea in religious rituals. Caves have been found where the insides where shaped so that they had very good acoustics. Anyway, someone would blow a horn in the cave at the right frequency, and everyone else in the cave thought that the Gods where taking over their bodies, or something like that.
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ogs
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Mechanical resonance is used in MRI scans too, it is the frequency of the radioactive sample that they put in your body that shows your insides (oh and loads of technical equipment!)
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elpaw
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(Original post by ogs)
Mechanical resonance is used in MRI scans too, it is the frequency of the radioactive sample that they put in your body that shows your insides (oh and loads of technical equipment!)
no, no and no.

Magnetic resonance is used in MRI scans, which scans for a signature frequency of hydrogen nuclei changing from one spin state to the other in an external magnetic field.


the method involving radioactive samples is the PET scan. a radiactive sample is introduced into the body, causing positron (beta-plus) emission, which annihilates with a nearby electron, releasing gamma radiation which is picked up by sensors, and a 3d computer model made of the parts where the radiactive sample reached.
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davey_boy
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(Original post by ogs)
Mechanical resonance is used in MRI scans too, it is the frequency of the radioactive sample that they put in your body that shows your insides (oh and loads of technical equipment!)
Erm MRI - magnetic resonance imaging, not mechanical. As far as I'm aware you don't need to have radioactive dyes put into your body to use an MRI scanner - I'll let you know for certain next Tuesday cos I'm having one, but I certainly don't remember reading that on the info sheet.
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shiny
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(Original post by davey_boy)
Erm MRI - magnetic resonance imaging, not mechanical. As far as I'm aware you don't need to have radioactive dyes put into your body to use an MRI scanner - I'll let you know for certain next Tuesday cos I'm having one, but I certainly don't remember reading that on the info sheet.
They use sometimes use contrast dyes in MRI but they are not radioactive .
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Jonatan
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(Original post by shiny)
They use sometimes use contrast dyes in MRI but they are not radioactive .
I would suspect that these contrast fluids contain some chemical compound of silicon and hydrogen. Hydrogen atoms bound to silicon has a quite different resonance frequency than hydrocarbons. This is also why you use TMS as a reference.
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Hoofbeat
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(Original post by Jonatan)
I would suspect that these contrast fluids contain some chemical compound of silicon and hydrogen. Hydrogen atoms bound to silicon has a quite different resonance frequency than hydrocarbons. This is also why you use TMS as a reference.
I had an MRI scan on my injured wrist about 2years ago and there was no radioactive dye involved. It is mainly used to detect tumours, or as in my case severe muscle/tissue damage.

Btw, spoke to my teacher today and he says that he does believe that when a fork "scratches" a plate and it makes my teeth feel funny then it is most likely that my facial cavities are indeed resonanting.
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