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Slide 1

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By Rachel Exact…read more

Slide 2

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What is natural frequency?
· When you hit an object it will vibrate, creating
sound waves.
· It will tend to vibrate at a single frequency or
set of frequencies.
· This frequency is known as that objects
natural frequency
· If the sound wave produced has a large
amplitude and a frequency within the range of
the human ear the sound will be audible…read more

Slide 3

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Forced vibrations
· You can force an object to oscillate at any
· Forced vibrations happen when there is an
periodic external driving force.
· The frequency of this is called the driving
frequency. If this is equal to the natural frequency
the amplitude will grow. This is RESONANCE.
· Resonance can be dangerous and destructive, if
the amplitude grows too much glass etc. can
shatter.…read more

Slide 4

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· Damping occurs when energy is lost to its
surroundings. It absorbs energy and reduces the
effect of resonance
· Damping forces include frictional forces like air
· Systems can be deliberately dampened to stop
oscillation and minimize the effects of resonance.
· It is often used to earthquake proof buildings.
· As damping increases: Amplitude decreases and
the resonant frequency gets lower.…read more

Slide 5

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Tacoma Narrows Bridge
· In 1940 in Tacoma, WA, USA, the Tacoma Narrows
suspension bridge collapsed 3months after its
· A steady cross wind created swirling air causing
the bridge to vibrate. Unfortunately these
vibration matched the natural frequency.
· Although many measures were taken, the bridge
continued to resonate and oscillate more and
more violently eventually becoming too much for
the structure, causing the bridge to collapse.…read more

Slide 6

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Tacoma bridge continued
· This event is well known among bridge engineers
and has allowed further technology in bridge
dampening to be developed.
· Other bridge disasters include 200 french soldiers
died as they were marching across a bridge,
collapsing it due to their marching over resonating.
Soldiers now have to break march when crossing a
bridge.…read more

Slide 7

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Slide 8

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