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-   -   Action - reaction : earth and walk (http://www.cfd-online.com/Forums/main/10014-action-reaction-earth-walk.html)

 Kevin Rogers October 4, 2005 19:44

Action - reaction : earth and walk

Does the earth move/rotate when we walk? Action and reaction law says it should. If it does even a bit, how much we can be sure? What's happening?

Thanks.

-K. R.

 diaw October 4, 2005 20:11

Re: Action - reaction : earth and walk

Yes, I would say that the Earth surely responds by an infinitesimal amount to each & every perturbation... but, it has ways & means of damping them into oblivion...

Much like the fly-into-train impact, only on a larger scale.

Ever sat in your car on a flyover road & 'felt' each and every passing vehicle - through the tarmac? It happens.

Beware of the 'butterfly effect'... Chaos reigns supreme - apparently... :)

diaw...

 Lars Ola Liavåg October 5, 2005 01:20

Re: Action - reaction : earth and walk

Since, on average, everybody pretty much walks in different directions all the time, I suppose the net effect on Earth's rotation is zero anyway. If, on the other hand, every creature on the planet were to turn e.g. east at exactly the same time, there might be a possibility that it could be registered.

 matej October 5, 2005 03:00

Re: Action - reaction : earth and walk

You all forgot the movement of the continents! If all Britons would gone to shore and paddle, they might get better weather down south (no offence - I enjoy weather in UK :o). I think I actually read this idea in some story.

The question is what would happen to earth rotation, if we moved this way all continents to one side of the globe...

matej

 faber October 5, 2005 03:27

Re: Action - reaction : earth and walk

I think there's a book by j.verne(?), cann't remember the title, in which a physician has to solve the task how much explosive is needed and where to blow it up to divert earth axis a bit more such that a sea somewhere would recede by certain distance - in order to disclose a coal bed.

Unfortunately, a draught causes a curtain to wipe off some zeroes on the physician's chalkboard and the action fails - thus, we don't know the right answer :)))

well, seriously: there's no doubt earth responds to every step of every live being. and there's no doubt as well, that we are not able to calculate how much: there're 6mld peple on earth, does anyone have a idea on what are they doing even in single one instant of time? plus the animals, plus ships casting off, plus car crashes plus aircraft landings, plus building demolitions plus........ minus damping via sea tides, minus damping via atmosphere... maybe one day we'll be as good in statistics as able to ESTIMATE it

 Steve October 5, 2005 04:30

Re: Action - reaction : earth and walk

Think of Brownian Motion. Although the net effect is zero, the Earth should jiggle a (tiny) bit.

 Ford Prefect October 5, 2005 10:28

Re: Action - reaction : earth and walk

"well, seriously: there's no doubt earth responds to every step of every live being. and there's no doubt as well, that we are not able to calculate how much: there're 6mld peple on earth, does anyone have a idea on what are they doing even in single one instant of time? plus the animals, plus ships casting off, plus car crashes plus aircraft landings, plus building demolitions plus........ minus damping via sea tides, minus damping via atmosphere... maybe one day we'll be as good in statistics as able to ESTIMATE it"

Well, the same thing could be said about turbulent motion... I'm sure human motion is quite predictable in a statistical sense. And then we can use some RANS method :)

To put it simple; rush hour - lots of ppl going to work/home and night - lots of ppl Not going to work/home

 diaw October 6, 2005 04:39

Re: Action - reaction : earth and walk

"Well, the same thing could be said about turbulent motion... I'm sure human motion is quite predictable in a statistical sense. And then we can use some RANS method :)

To put it simple; rush hour - lots of ppl going to work/home and night - lots of ppl Not going to work/home "

I wonder what the units of this human transport should be? "heads/second"? "frustrations/minute"...

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