IIT JEE , AIEEE Forum - Physics , Mechanics

anil_kapoor

Every thing has its natural frequency...

wat does this mean by?

a pen, a buk, a pair of spectacles, the calculator......etc has got their natural frequency? they r'nt goin 2 oscillate if u push them in air/space...

what does this natural frequency mean by.......

sankydreams

The freq here means the frequency with which the atoms or constituent particles oscillate in them considering u know that atoms oscillate in all states of matter, dont ask me the reason :-)
Correct if o m wrong
rate if this helps u...

master_purav

All things have their natural frequency. As explained by sankydreams all things oscillate due to oscillations of atoms and the resulatnat oscillation is called natural frequency. That means all things around you are actually oscillating!!

When requency due to some external periodic force matches this, the object may break. This fact is taken in consideration while contrusting huge structures and the best example of it is bridge.

The bridge has a shape such that the centre part of it undergoes maximum 'bending' due to its owm weight and the restoring force pushes it upwards and thus bridges tend to oscillate with some 'natural' frequency. You might have experienced that when a heavy vehicle passes from the bridge, bridge oscillates with a slightly larger amplitude. Due to air (during storms) if the frequency due to force exerted by air on the bridge matches the natural frequency then the bridge may collapse. There are many examples of this fact in history. That is the reason that soldiers do not march on bridges.

parismulye

the frequency of the buildings is related to the frequencies formed due to earthquake once it happened in a country thatapp all the buidings having floors 6-12 remain unaffected but others fell due to the impact of earthquake i have seen this in a discovery show

master_purav

Actually whenever there is an earthquake, the freqeuncy of the earthquake matches the natural frequency of building and so it collapses.

Normally taller buildings are more earthquake-prone because they have higher natural frequency closer to the normal one of an average earthquake. When the condition of resonance develops, the amplitude increses so much that the nirmal structure of building and its cement-concrete skeleton cannot withstand it. And so it collapses. But during some unusual earthquakes, like the one that took place in Mexico city once, the frequency was lower than normal (close to naturaql frequency of small buildings). During that earthquake small buildings collapses and taller ones were saved.

One of the modern ways of building earthquake proof buildings is that the natural frequency of the building can be changed by hanging a heavy ball or something like that like a tall pendulum from top of bldg. So that during earthquake the frequency of bldg increases but does not become equal or near to the one of the earthquake and so condition of resonance does not take place and so bldg is saved.

anil_kapoor

hi, well wat i think is tat as every thing is placed on earth....(case-I)
as the earth has small vibrations due 2 certain tectonic plate movements+rotation /revolution i know thats almost negligible..... which must causes induced sort of vibrations on the body placed.
so is'nt tat its natural freq. (ext disturbance)
4 bridges the movement of air might adds up it the vibration to it...(ext disturbance)
now ...if v talk abt atomic levels the vibration dont u think tat must cancell out each others effect ?
of if u c the army marching on a bridge hav got a gud mag of freq ...does tat sounds u perfect tat virations at atomic level matches the vibrations of d feets frm army men?

now(case -II)
in vaccum sound can not travel so no natural ferq and no forced oscillation concept(coz forced oscillation concept is only applicable when desipative forces r their ...)
also no buk /site discribes tat natural freq is in vaccu....
if anybody find any source do tell me.....pls.
pls think abt it.....

spideyunlimited

1) regarding the part about marching army
in China some years ago as an experiment 50,000 people got together and started thumping their feet synchronously to a rhythm . the frequency of the oscillations developed in the ground matched with 2 buildings nearby and they collapsed!

2) a medium is not required for resonance due to matching of natural frequency.. radio transmissitors work on the frequency fundamentals too.

master_purav

Actually, all materials are elastic to less or more extent. That means that when any body is acted upon by any force a restoring force quickly develops. Now the surface of that material never remains in equilibrium because of its momentum. Thus it sways to and fro. This is due to inter-atomic attractive forces. so i think that the natural frequency must be related to inter-atomic attraction more than atomic vibrations. But one thing is sure that all things have natural frequency with which they are oscillating. The frequency can be very small to large, just its amplitude is small. That means that the soldiers can match the natural frequency of the bridge.

I dont know about vaccuum.

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