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Mechanical Resonance

Posted by Gale Bernhardt Dec 7, 2007

I have to admit that I snuck out on Wednesday for a mountain bike ride. I knew snow was heading our way Friday and through the weekend. With temperatures in the 40s and the trail in great condition, I was a happy camper.

 

The particular trail I rode has some significant sections of rock gardens. It has been just recently, in the past two months, that I am able to ride all the way through the rock gardens.

 

I was reminded on Wednesday, that successful rock garden riding is never a guarantee and that getting ever so slightly off of my preferred route can bring about disaster.

 

 

On one of the downhill sections, I was carrying some speed. I missed my preferred turn, which put me into an area where the rocks happen to throw me into oscillations. These oscillations are not a problem unless they match the natural frequency of the system (me and my bike).

 

 

First, let me describe how this feels. I am bouncing along and traveling through the rock garden, and slightly gaining speed. The bouncing up and down begins to take a rhythmic feel. At first the rhythm is somewhat relaxing and I think "No problem it is good for me to ride non-preferred routes to increase my skills."

 

 

But, within a short amount of time I realized that I was gaining more altitude with each bounce and the rhythm was increasing. As I feel this oscillation beginning to become a problem, I can't help but think of the Tacoma Bridge disaster. (I know, I know, strange thing to think about, but that is what popped into my head.)

 

 

I'm thinking, "If I reach mechanical resonance, I'm going to go flying off of this bike and the result will surely require Band-Aids."

 

 

The entire scene seemed to go on forever, but probably only took about five seconds to unfold.

 

 

Luckily, I managed to avoid mechanical resonance and kept riding without putting a foot down. I can't tell you how I did it, only that it happened.

 

 

If you have not seen the disastrous results of mechanical resonance, you can see footage of the Tacoma Bridge disaster below the header "Film of collapse" at this link: http://en.wikipedia.org/wiki/Tacoma_Bridge#Galloping_Gertie . A longer, and color, video is here.

 

 

Have a good weekend and may you never reach mechanical resonance.

 

 

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