Question about Natural Frequency and Resonance

In summary, the conversation discusses the concept of resonance and how it can potentially lead to destruction of objects. The example of Nikola Tesla's claim of being able to split the Earth in two with resonance is mentioned, as well as the idea of using a variable frequency oscillator to create standing waves and potentially destroy objects. The conversation also touches on the factors that determine the amplitude of a standing wave, such as the quality factor and the driving source. The Tacoma Narrows Bridge is brought up as an example, with the discussion focusing on whether it was the wind or the standing wave that caused its collapse. Ultimately, it is concluded that the wind caused the bridge to hit its natural frequency and be destroyed. The conversation also delves into the concept of Q
  • #1
Thundagere
159
0
So, I was reading a book on Nikola Tesla the other day, and it said that he said that he could theoretically split the Earth in two with resonance.
If I had a variable frequency oscillator, and I knew the natural frequency of an object, obviously I could create a standing wave. But, could I, as Tesla states, actually destroy it? Just clamp on the generator, and come back later to find it destroyde?
Secondly, what determines the amplitude of a standing wave set up by natural frequency. When you have a metal piece or a length of string it's the length that determines the wavelength, but what determines the amplitude?
Thanks for any help!

EDIT: Something else that's been bugging me...the Tacoma Narrows Bridge. The book said it was destroyed by winds hitting the natural frequency, which I presumed set up a standing wave. However, this seems...off, to me.. How could the winds hit and more importantly HOLD that frequency? Was it mere lack of structural integrity that destroyed this bridge,or was it the standing wave?
 
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  • #3
So the winds did cause it to hit the natural frequency and be destroyed? But how was it that the winds maintained that frequency for so long without changing?
 
  • #4
Thundagere said:
So the winds did cause it to hit the natural frequency and be destroyed? But how was it that the winds maintained that frequency for so long without changing?

I'm not sure the wind needs to have a frequency.
 
  • #5
Flutter is a self-feeding and potentially destructive vibration where aerodynamic forces on an object couple with a structure's natural mode of vibration to produce rapid periodic motion.
I took this to mean it matches the natural frequency, especially since "natural" is linked to natural frequency. Or am I missing something here?
 
  • #6
The winds were steady, not periodic. However, a steady wind blowing across a surface will produce wind vortices at a periodic rate, and it is this period that was in resonance with the Tacoma Narrows Bridge.

Think of a flag fluttering back and forth while a steady wind is blowing.
 
  • #7
So essentially the ripples caused by the wind matched the frequency, which destroyed it...
Falling back to the original question, does that mean that, if I had a variable frequency oscillator, I could theoretically destroy anything, provided it was the same substance throughout?
 
  • #8
Thundagere said:
So, I was reading a book on Nikola Tesla the other day, and it said that he said that he could theoretically split the Earth in two with resonance.
If I had a variable frequency oscillator, and I knew the natural frequency of an object, obviously I could create a standing wave. But, could I, as Tesla states, actually destroy it? Just clamp on the generator, and come back later to find it destroyde?
Secondly, what determines the amplitude of a standing wave set up by natural frequency. When you have a metal piece or a length of string it's the length that determines the wavelength, but what determines the amplitude?
Thanks for any help!

EDIT: Something else that's been bugging me...the Tacoma Narrows Bridge. The book said it was destroyed by winds hitting the natural frequency, which I presumed set up a standing wave. However, this seems...off, to me.. How could the winds hit and more importantly HOLD that frequency? Was it mere lack of structural integrity that destroyed this bridge,or was it the standing wave?

Thundagere said:
So essentially the ripples caused by the wind matched the frequency, which destroyed it...
Falling back to the original question, does that mean that, if I had a variable frequency oscillator, I could theoretically destroy anything, provided it was the same substance throughout?

The amplitude of the oscillation at resonance depends on the "Q" or quality factor, and the amplitude of the driving source. The Q factor depends on how much damping there is in the structure. Thin crystal wine glasses can have a high Q factor, due to their thinness and hardness. You may have seen demonstrations of breaking wine glasses with and adjacent speaker, but you won't see the same demonstrations with a standard glass (unless the sound levels are crazy high).


EDIT -- here's a link for more reading:

http://en.wikipedia.org/wiki/Q_factor

.
 

1. What is natural frequency?

Natural frequency is the frequency at which an object or system naturally vibrates or oscillates when it is disturbed. It is determined by the physical properties of the object or system, such as its mass, stiffness, and damping.

2. How is natural frequency related to resonance?

Natural frequency and resonance are closely related. When a force is applied to an object or system at its natural frequency, it will cause the object to vibrate with a large amplitude. This is known as resonance and can lead to destructive effects if not controlled.

3. Can natural frequency be changed?

Yes, natural frequency can be changed by altering the physical properties of the object or system. For example, the stiffness of a spring can be changed by adjusting its material or length, which will affect its natural frequency.

4. What are some real-world examples of natural frequency and resonance?

Examples of natural frequency and resonance can be found in many everyday objects and systems. Some common examples include a child on a swing, a guitar string, and a tuning fork. In engineering, natural frequency and resonance are important considerations in building and bridge design.

5. How can resonance be prevented or controlled?

Resonance can be prevented or controlled in various ways, depending on the specific situation. Some common methods include using damping materials to dissipate vibrational energy, changing the physical properties of the object or system, or using vibration isolation techniques. In engineering, resonance is often avoided by designing structures with a natural frequency outside of the operating frequency range.

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