The 'natural frequency' of an object. What does this mean?

[Couperin]

What does it mean to say that something, for example a bridge, has a natural frequency? Does this have anything to do with how long it is?

 

[Chi Meson]

Like a swing in a playground, if you push anything, it will oscillate; that is, it will swing back and forth at a certain rate. This rate is called the natural frequency. All things that are not completely inelastic (like warm clay) will do this. buildings and bridges, bricks, rocks, trees, planets, everything.

 

[turdferguson]

Its what Tesla supposedly used to build his earthquake machine. Its also the reason why soldiers have to break their march when going across bridges

 

[Astronuc]

Does this have anything to do with how long it is?

Yes, length is one factor. Other factors include mass and rigidity or stiffness. Structures have natural frequencies, and members or components have their own natural frequencies, and then there are couplings or coupled interactions between components.

Nearly all objects, when hit or struck or plucked or strummed or somehow disturbed, will vibrate. If you drop a meter stick or pencil on the floor, it will begin to vibrate. If you pluck a guitar string, it will begin to vibrate. If you blow over the top of a pop bottle, the air inside will vibrate. When each of these objects vibrate, they tend to vibrate at a particular frequency or a set of frequencies. The frequency or frequencies at which an object tends to vibrate with when hit, struck, plucked, strummed or somehow disturbed is known as the natural frequency of the object.

from http://www.glenbrook.k12.il.us/GBSSCI/PHYS/CLASS/sound/u11l4a.html

Frequency at which a mechanical system will vibrate freely. A pendulum, for example, always oscillates at the same frequency when set in motion. More complicated systems, such as bridges, also vibrate with a fixed natural frequency. If a varying force with a frequency equal to the natural frequency is applied to such an object the vibrations can become violent, a phenomenon known as resonance.

http://www.tiscali.co.uk/reference/encyclopaedia/hutchinson/m0025332.html

 

[Feldoh]

Its what Tesla supposedly used to build his earthquake machine. Its also the reason why soldiers have to break their march when going across bridges

Somebody watches mythbusters

 

[Couperin]

Thank you all very much.