using principle of RESONANCE to break things

[SysBio]

Hi everyone,

Im learning about the basics of resonance, and I am just wondering why it is not observed more often in everyday objects.

 

For example, if one produces a frequency that is just the right frequency of a wine glass, it shatters.

So why dont common objects around us start visibly vibrating even though there are many different sound waves constantly produced around us? (For example, there could be music played loudly, someone shouting or banging a table loudly, and arn't there a lot of other waves circulating around us from wireless devices?)

 

I'll take a shot:

Most solid objects around us vibrate at a frequency that is relatively HIGH, and most sound waves we precieve have low frequency? The type of waves that would be required to shatter common solid objects could not be produced "accidently"?

 

 

Thanks in advance....I hope someone answers this question !

[Kyrisch]

Well, I think it has more to do with noise pollution. Remember that sound is a wave, and waves can occupy the same space at the same time (it's called interference). Because of this, the sheer amount of sound at any given time will not increase the chance, but actually prevent resonance from occurring because the sound will be less pure. (Imagine you and a friend swinging a jumprope at the same frequency and phase, and then at the same frequency and out-of-phase. No resonance will occur in the second case).

[Cap'n Refsmmat]

There are several reasons.

 

• Most sounds aren't pure tones sticking to one frequency. If something resonates at 414Hz and you start talking, you might hit 414Hz occasionally (if you have a rather high-pitch voice), but never for more than a split second.
  
• Damping. Some things, like wine glasses, have little to slow the vibration and absorb its energy. Other things -- like, say, something sitting on carpeting -- lose energy quickly. The carpet damps the vibrations.
  

 

But you can have cases of very interesting resonance. My dad once worked on an RV which had numerous internal parts (cabinet doors, a TV mounted on the wall, fixtures, anything) which coincidentally resonated at a frequency very close to the frequency the cylinders of the engine fired at at idle speed. When sitting at idle, nearly everything inside the RV would start vibrating -- cabinet doors would rattle, the TV would shake on its mount, and so on. They had the option of fixing every little component on the RV... but instead they just changed the engine idle speed.

 

There was also the case of mail trucks whose rearview mirrors started vibrating whenever the truck idled... they had to add bracing to the mirror mount so it wouldn't vibrate so much.

[SysBio]

ok....thanks for the replies...and cool example with the RV

 

yeah i didn't realize that you need a pure sound wave at a given frequeny, so that explains why even if the given frequency is produced in everyday noise, it would not cause resonance

 

But can someone comment on the resonating frequency of most common solid objects vs. the frequency of common sounds?

[JPGreco]

Well, define most common objects. Objects made of multiple materials would require multiple wave lengths of sound to resonate each material, but the multiple wave lengths would interfere with each other causing none of the material to vibrate or to barely vibrate.

The wine glass is one of the simplest examples because the material is very fragile and pure.

Resonance is like pushing a kid on a swing. You need to push at the right time to build energy so the kid swings farther and farther. If you push at the wrong time or with the wrong amount of energy, it doesn't work right and the swing (vibration) starts to lose energy. If you push right (correct frequency) you can get a swing really moving.

 

Aspects of resonance are all around us, but not at a destructive level.