AboutKevin Johnson Expertise I will try to answer any question in physics, but I do not provide homework solutions or project ideas. I have some teaching experience at university level but I am also skilled at explaining things in simple terms.
My specialty areas are granular materials, computational physics, particle physics, quantum physics, econophysics and general physics.
Questions in GERMAN are welcome, too.
Experience I have graduated in physics, specialized in theoretical particle physics and quantum field theory, worked in the area of econophysics and am currently working on my PhD in granular materials and computational physics. I have some tutoring and teaching experience at University level.
Education/Credentials German Diploma in Physics (equivalent to M.Sc)
Question I once saw the people at Myth Busters shatter a wine glass by finding its resonance frequency.
I understand that all things have a resonance frequency. Can anything be destroyed (i.e. shaken apart) by emitting its resonance frequency at it at high enough volume?
Also, are all resonance frequencies as simple as it is for a wine glass or do some have very complex one involving a multitude of frequencies?
Answer Hello Spencer,
I will answer all your questions in one answer here.
Your questions were:
I once saw the people at Myth Busters shatter a wine glass by finding its resonance frequency.
I understand that all things have a resonance frequency. Can anything be destroyed (i.e. shaken apart) by emitting its resonance frequency at it at high enough volume?
Also, are all resonance frequencies as simple as it is for a wine glass or do some have very complex one involving a multitude of frequencies?
If you find the resonance frequency of a wine glass, you can make it shatter by emitting it back at it with enough force.
How does this frequency change when it is in different mediums: water, for example?
Also, dwhat effect does this have on the volume required to break a glass (or any item for that matter)?
My answer:
You can find the resonance frequency of a glass by rubbing a wet finger along the top of the glass. This effect is used in musical performances of a "glass harmonica". The glasses are filled with water to different levels in order to produce the different frequencies for a musical melody.
The reason for the difference in pitch for glasses filled to different heights is that the speed of sound is different in different media (e.g. air versus water). The speed of sound is higher in water and so the pitch of a water filled glass is also higher.
The exact mechanisms of resonance in a wine glass are too complex to discuss here, but the principal effect is that there is a so called "standing wave" that builds up in the glass. This is a vibration where the nodes of the waves (the parts that do not move) are stationary, and so are the arcs of the wave. This leads to relatively large displacements of those parts of the glass that are at an arc of the wave. If these displacements are large enough, the glass breaks there and shatters.
In order to destroy something by resonance you need to feed it enough energy to break the structure. This energy only depends on the structure to be destoyed and is independent of the medium by which the sound energy is transferred. But different media conduct sound energy with different efficiencies. Water for example conducts sound much better than air, and solids usually conduct sound even better.
Different objects have different resonance frequencies, but one only speaks of resonance if there is one frequency at which the vibration is not damped. The non-resonance frequencies are damped and only the resonance frequency (and possibly integer multitudes of it) remain in the object.
Most objects don't have such a single resonance frequency and thus don't exhibit the phenomenon of resonance. All frequencies are damped.
More complex structures may exhibit several resonance frequencies, but this is due to different parts of the structure exhibiting different resonance frequencies at different modes of vibration. This is used in musical instruments, like violins or pianos, where wooden casings resonate at all musical notes (but by different vibration patterns).
So you cannot destroy most things by resonance, since most things do not exhibit resonance to a degree useful for this purpose. You would need extreme sound intensities that could only be achieved by a nearby explosion, and I would not call that a resonance destruction any more.
In engineering, one must take care that buildings and structures do not exhibit resonance frequencies. The most famous bad example is the Tacoma Narrows Bridge, where resonances were excited by winds and the bridge began swaying and twisting uncontrollably, until it collapsed under the stress, because the resonance frequency was not damped. The pedestrian Millenium Bridge over the Thames river in London also initially suffered from resonances until dampers were installed.
