What could have brought down the wall
of
The Sunday Nation
Nairobi,
27 July 2014
Charles Githiomi refers to Philip Ochieng’s article in the
Saturday Nation of 5th July
2014, that mentioned “A biblical cock-and bull story that
First, let me explain what resonance is. Every object has a natural vibration frequency. When struck, it vibrates at this rate.
The natural frequency depends on the nature of the material (whether it is metal, plastic, glass etc) and on the shape of the object (is it flat, circular, square, spherical etc?)
If an object if vibrated at a rate equal to its natural frequency, it will respond with very high amplitude. Note: amplitude is the “size” of a vibration, while frequency is the rate.
Motorists know this all too well: when the wheels of a car are unbalanced, the whole vehicle vibrates violently at a certain speed and then settles down when driven faster. For most cars this happens anywhere between 60km/h and 100km/h. This violent shaking is a result of resonance.
An unbalanced wheel has more weight on one side so, as it turns round, the heavier part will be moving up and down. The rate of this up-down movement will depend on how fast wheel is rotating, in other words, on the speed of the car.
At a certain speed, the up-down motion of the heavier part of the wheel will be at exactly the same rate as the natural frequency of the car’s suspension and the whole vehicle will shake violently. Resonance
If you drive faster, the shaking dies off but as you begin to slow down, it comes back at the same speed. If you drove the car several minutes at this resonance-causing speed, there is a good chance that many pieces will come crumbling down!
After understanding the concept of resonance, we can now tackle Charles’s question: “could resonance created by the human and trumpet sounds have destabilized the atoms in the rocks to the point of crumbling?” I don’t think so. It can’t have been due to the sound of the trumpets.
The reason is that the frequency of audible sound is too high above the natural frequency of a stone wall. Therefore, it can’t cause resonance. I suspect that the wall could have collapsed due to the rhythmic stumping of feet as Joshua’s army marched round the city. This could have caused an earth tremor whose frequency matched that of the wall.
It is because of this kind of effect that soldiers have to break their march and walk normally when going over a bridge. The rhythmic stumping of feet has been known to bring down bridges.
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