About DCML-talk and the center of the Earth

Daniel van Eijmeren dve at kabelfoon.nl
Sun Mar 21 12:55:32 CET 2004


CORD WILJES to SOREN KRARUP OLESEN, 20-03-2004:

>> If the gravity arises from mass only, you'd certainly be 
>> affected by those upper shells as well, in other words, 
>> you'd experience weightlessness long before you reach the 
>> middle of the Earth.

> Please find my reply here: 
> http://www.dcml-talk.org/read.php?f=1&i=226&t=226

Why do you put your reply elsewhere? The subject about the center of the 
Earth, is an exploration of matters in a Disney story. It's still related. 
If people for no reason would write about the center of the "new planet" 
Sedna, *then* it would be off-topic.

Please, I don't want to go to do different places to read about one 
subject. That will result in messages like: "If you want to know more, 
visit www.this-or-that-site.com!" 

Story-related subjects like these, are part of the reasons why I'm 
subscribed to DCML.

I hope you won't mind if I fully quote your message from the above 
mentioned URL. It makes it easier for me to archive your interesting 
message. 

And it makes it easier for me to reply to the subject. 
(See the end of this e-mail.)

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Center of the earth
Author: Cord (---.dip.t-dialin.net)
Date:   03-20-04 04:00

Theresa wrote: 

>> The further down you dig yourself, the smaller the earth-'ball' that
>> creates a gravity on you gets. THe mass that is above you, 
>> a 'shell' of earth, wouldn't affect you.
>> So the downwards pull of gravity gets less and less, until 
>> in the middle you'd be weightless.

If you were in space in the middle between two planets of equal mass then
both planets gravitational pull would cancel out. Essentially there would be
no net force at all. (I know that you know that better than me)

But in the case of digging to the earth's core you have to consider that
those layers of the earth you already digged through are (a little bit)
nearer to you than the mass in the equivalent layer on the other side of the
earth. As the gravitational pull decreases with the square of the distance
they do not exactly cancel out. There is little less net force pulling you to
the core than the imaginary "small earth ball" under you would extract
without the layers of earth above you.

Søren wrote:
> If the gravity arises from mass only, you'd certainly be affected by
> those upper shells as well, in other words, you'd experience
> weightlessness long before you reach the middle of the Earth.

The effect I described above decreases as you get nearer to the center of the
earth because the layers of earth above you (pulling you "up") get further
away and their equivalent mass on the other site of the earth's center
(pulling you "down") gets nearer. Only at the eath's center do you have zero
gravity because only there you have equal mass "above" and "below" you.

It would be quite interesting to experience the YoYo-effect of falling down a
tunnel through to the center of the earth (zero gravity) where the energy of
motion would carry you to the other side of the earth (losses by air friction
deducted) and then back again.

You would feel like falling all the time: execept in the middle of the earth
and at the two return points on each side. At all of theses three points you
would feel weightless.

Cord

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I want to note that there's a (Dutch?) story about Donald falling through the 
Earth, like a YoYo, going from one side to the other, and back. It must be a 
story from the early 1980s or the mid-1980s. At least that was when it must 
have been published in the Dutch weekly. It was about ten pages, I think. 

Are there people here who recognize this story? 

BTW. I remember the story as very funny. But I was still a kid back then, 
and kids are not capable to judge whether a Duck story is good or not. They 
have to re-read the story as adult collectors, before they can give a good 
judgement. Right? :-) I'm saying this, because this is often the feeling I 
get, after recommending a story from my youth without rereading it. People 
might jump on me and ask if I'm blind or crazy, for appreciating such a lousy 
story. And then I automatically start to defend myself by saying that I was 
only a kid back then... As if kids are not old and wise enough to fully enjoy 
children's stories! :-)

--- Daniël

"Stop! You don't know what you're doing to yourself"
(Which Barks story?) :-)
Hint #1: These words are spoken by Donald.
Hint #2: Donald is talking to an animal.
Hint #3: Loss of hair.




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