# Light as a feather stiff as a board and levitation

**URL:** <https://boards.straightdope.com/t/light-as-a-feather-stiff-as-a-board-and-levitation/390763>\
**Category:** Factual Questions\
**Created:** [February 4, 2007, 7:34am UTC](https://boards.straightdope.com/t/light-as-a-feather-stiff-as-a-board-and-levitation/390763 "2007-02-04T07:34:42Z")\
**Posts on this page:** 4\
**Page:** 3

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**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\
**Post date:** [February 7, 2007, 1:06am UTC](https://boards.straightdope.com/t/light-as-a-feather-stiff-as-a-board-and-levitation/390763/41 "2007-02-07T01:06:48Z")

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[QUOTE=Chronos]  
In order to lift a person a certain height, you need a total energy at least equal to the person’s weight times the height you want to lift them. And while that energy could in principle be delivered in a single brief impact, it’s likely to hurt.  
[/QUOTE]  
Doesn’t weight times height lifted give you \*work \* (force x distance)?

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**Author:** ![Bill\_Door](https://avatars.discourse-cdn.com/v4/letter/b/50afbb/32.png) [@Bill\_Door](https://boards.straightdope.com/u/Bill_Door)\
**Post date:** [February 7, 2007, 3:33am UTC](https://boards.straightdope.com/t/light-as-a-feather-stiff-as-a-board-and-levitation/390763/42 "2007-02-07T03:33:51Z")

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[QUOTE=glee]  
(snip)In fact, a concrete suspension bridge, the Tacoma Narrows Bridge, was destroyed by resonance vibrations set up by winds acting on the bridge. Today’s bridges are constructed to prevent or minimize this type of wind resonance effects.’

[QUOTE]

Sorry, this is an example of bad science propagated by lower level textbooks. It was wind, but NOT resonance. The actual mechanism of collapse of the Tacoma Narrows Bridge, (Galloping Gertie) was a good deal more complex. At the 42 mile per hour wind speed directly observed during the catastrophic failure of the bridge the frequency of the vibrations recorded were completely unsychronized with any natural resonance in the structure.

[Here](http://www.ketchum.org/billah/Billah-Scanlan.pdf) and [here](http://www.vibrationdata.com/Tacoma.htm) are a couple of links to more recent ideas about the bridge collapse.

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**Author:** ![bouv](https://avatars.discourse-cdn.com/v4/letter/b/bc8723/32.png) [@bouv](https://boards.straightdope.com/u/bouv)\
**Post date:** [February 7, 2007, 3:40am UTC](https://boards.straightdope.com/t/light-as-a-feather-stiff-as-a-board-and-levitation/390763/43 "2007-02-07T03:40:52Z")

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[QUOTE=FRDE]  
Doing some highly scientific tests with two fingers of each hand pushing up under the desk, I get different results if I apply upwards pressure gradually, from what happens when I apply it rapidly.  
[/QUOTE]

Well, I tried this a bit myself, and it seems that by doing it rapidly, I’m more likely to accidentally use my wrist and arm muscles in the process.

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**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\
**Post date:** [February 7, 2007, 3:50am UTC](https://boards.straightdope.com/t/light-as-a-feather-stiff-as-a-board-and-levitation/390763/44 "2007-02-07T03:50:45Z")

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> [@](#):
>
> Doesn’t weight times height lifted give you work (force x distance)?

Yes, but work is just another word for mechanically-transfered energy. You need energy to do work.

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