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Author Topic: Gravity At The Center Of The Earth  (Read 28407 times)

Offline neilep

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Gravity At The Center Of The Earth
« on: 06/05/2007 16:41:41 »
Hmmm..perhaps this should be in the Physics section !!

I think it should but will allow someone else to move it because I'm lethargic right now.



Say for instance there was conditions at the center of the Earth that could sustain Human life from an environmental pint of view (Very unlikely I know)......but it it were possible.

What would the conditions be like ?..would I float about in a a gravity-less state ? or would I be pulled apart or squashed ?....or something else ?


 

paul.fr

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Gravity At The Center Of The Earth
« Reply #1 on: 06/05/2007 17:00:45 »
that depends on what you mean by centre of the earth! if you were to drill a hole/tunnel from one point on the earth to another, at the very centre of that hole/tunnel you would not feel the pull one way or the other. if you were slightly off centre then thats another question.
 

Offline neilep

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« Reply #2 on: 06/05/2007 17:09:39 »
that depends on what you mean by centre of the earth! if you were to drill a hole/tunnel from one point on the earth to another, at the very centre of that hole/tunnel you would not feel the pull one way or the other. if you were slightly off centre then thats another question.


Yep..I mean right at the center....so If I don't feel any pull...does  that mean the pressure inside my body will explode me ?

I imagine there would be a large enough area where the gravity is slight either way to enjoy flying fun !!
 

Offline Seany

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« Reply #3 on: 06/05/2007 17:18:51 »
Neily... If you go underwater that deep.. Our lungs explode and all our internal organs, because of the pressure. Imagine under all that water, and near the core of the earth?
 

Offline neilep

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« Reply #4 on: 06/05/2007 17:25:05 »
Hmmm..Thanks Seany !!..what happens if we dismiss the pressure thingy ?...will it be ok to have fun at the center of the earth ?
 

Offline Seany

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« Reply #5 on: 06/05/2007 17:26:59 »
Err.. Apart from the intense heat........ Err.. Maybe?

Oh.. Also the gravity would be stronger there, so we might still get squashed.. Like, so that we're the size of a pen.. So we'll still probably die. ;)
 

Offline neilep

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« Reply #6 on: 06/05/2007 17:52:41 »
Err.. Apart from the intense heat........ Err.. Maybe?

Oh.. Also the gravity would be stronger there, so we might still get squashed.. Like, so that we're the size of a pen.. So we'll still probably die. ;)

That's not nice !!..me does not want to die at the center of the Earth.... ;)


Ok....lets change the 'object ' of the question.

Say I had a football made out of something which is impervious to heat, pressure and anything else that has a tendency to make conditions intolerable.....and that there was a cavity the size of football pitch (cubed) in the center of the Earth.....what would happen to the ball ?
 

another_someone

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Gravity At The Center Of The Earth
« Reply #7 on: 06/05/2007 18:15:26 »
Neily... If you go underwater that deep.. Our lungs explode and all our internal organs, because of the pressure. Imagine under all that water, and near the core of the earth?

Actually, if anything, your lungs will implode rather than explode, but that is only if you do not equalise air pressure within them.  The bigger problem you have is the effect of gasses dissolving into the blood at high pressure having all sorts of physiological effects.
 

Offline that mad man

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« Reply #8 on: 06/05/2007 18:18:15 »
If you were able to be at the very centre then I think the gravity would be zero so the ball would be weightless and float.

Bee



 

another_someone

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« Reply #9 on: 06/05/2007 18:24:19 »
The gravitational pull at the centre of the Earth cannot be greater than at the surface of the Earth, since the amount of matter around you is no greater than the amount of matter beneath your feet when you are at the centre of the Earth.

In fact, as Paul has suggested, at the very centre of the Earth, the gravity from all sides will cancel out, making a nett zero gravity.  Away from the centre, there will be a gravitational pull (upwards, since all the mass of the Earth is now above you), but it will only be a very slight pull, since it is still the case that most of the gravity will be cancelled out by gravitational pull elsewhere.

What will be an issue is not the nett gravitational pull, but the gravitational tidal forces (although I doubt these will be enough to cause genuine harm to you).  What I mean by the tidal forces is that on the surface of the Earth, the gravitation pull at any point, and at a point about 1 centimetre away from that point, will be very similar, so although gravity will effect all parts of your body, it will effect it equally.  At the centre of the Earth, the gravitational pull at one point may be very different from the gravitational pull at another point close by; so although the actual gravitational pull will only be small, it could nonetheless be pulling your head in one direction, your feet in another, and your arms elsewhere.  Our bodies were not designed to be pulled apart like that, although because of the very small forces actually doing the pulling apart, it may not actually do any more harm than maybe cause motion sickness.
 

Offline JimBob

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« Reply #10 on: 06/05/2007 19:31:23 »
I believe what everyone is missing is that the null point for gravitational forces at the center of the earth is just that - a point. Around that null point is molten metal under enormous pressure - millions of PSI - and since nature abhors a vacuum that single pint will already be occupied. The pressure at that depth would overcome any tidal forces as would the compounded angular momentum of all the material above you. I doubt your chances of survival are not good. No, not good at all. Bye, bye, my friend.  [:0]
 

Offline neilep

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« Reply #11 on: 06/05/2007 20:27:45 »
Jimmy Boy....my question allows for the facility for it to be of a hospitable nature !!

So, it would not be " bye bye my friend "..it would  " come on over and have some fun friend"...YAYYYYYYYYY !!!
 

Offline JimBob

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« Reply #12 on: 06/05/2007 22:16:11 »
Ok, science fiction time, huh?
 

another_someone

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« Reply #13 on: 07/05/2007 01:03:42 »
Ok, science fiction time, huh?

A more charitable description would be a Gedankenexperiment :)
 

jolly

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Gravity At The Center Of The Earth
« Reply #14 on: 07/05/2007 10:03:28 »

That's not nice !!..me does not want to die at the center of the Earth.... ;)


Ok....lets change the 'object ' of the question.

Say I had a football made out of something which is impervious to heat, pressure and anything else that has a tendency to make conditions intolerable.....and that there was a cavity the size of football pitch (cubed) in the center of the Earth.....what would happen to the ball ?

It would sit on the central spot- in the middle of the pitch and not move anywhere!
 

jolly

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Gravity At The Center Of The Earth
« Reply #15 on: 07/05/2007 10:14:03 »
The gravitational pull at the centre of the Earth cannot be greater than at the surface of the Earth,

May I ask how you know that?

since the amount of matter around you is no greater than the amount of matter beneath your feet when you are at the centre of the Earth.

This explaination is about the center of the earth not the crust!


In fact, as Paul has suggested, at the very centre of the Earth, the gravity from all sides will cancel out, making a nett zero gravity.  Away from the centre, there will be a gravitational pull (upwards, since all the mass of the Earth is now above you), but it will only be a very slight pull, since it is still the case that most of the gravity will be cancelled out by gravitational pull elsewhere.

I do not agree with this statement! As I feel the Earths gravity is created by more than just mass!

What will be an issue is not the nett gravitational pull, but the gravitational tidal forces (although I doubt these will be enough to cause genuine harm to you).  What I mean by the tidal forces is that on the surface of the Earth, the gravitation pull at any point, and at a point about 1 centimetre away from that point, will be very similar, so although gravity will effect all parts of your body, it will effect it equally.  At the centre of the Earth, the gravitational pull at one point may be very different from the gravitational pull at another point close by; so although the actual gravitational pull will only be small,

I feel that this is incorrect as the gravitational pull from the earth will increase the closer you get to the center realitive to your mass!

it could nonetheless be pulling your head in one direction, your feet in another, and your arms elsewhere.  Our bodies were not designed to be pulled apart like that, although because of the very small forces actually doing the pulling apart, it may not actually do any more harm than maybe cause motion sickness.

Considering the fact that we hav'nt been there and the idea of going there is far to risky considering we could damage the earths. This is assumption but I like it.X
« Last Edit: 07/05/2007 10:19:59 by jolly »
 

another_someone

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« Reply #16 on: 07/05/2007 11:19:16 »
The gravitational pull at the centre of the Earth cannot be greater than at the surface of the Earth,

May I ask how you know that?

The same way that I know the Sun will rise tomorrow - I extrapolate from what I do know into what I do not know.  I may be wrong, maybe the Sun will not rise tomorrow, despite my experience of every previous morning when I have observed the Sun to rise, it may yet prove that my extrapolation of existing knowledge will prove to be false; but if we do not extrapolate based upon what we do know, then we are simply left with a total absence in our ability to predict anything - which serves us no good whatsoever.

I feel that this is incorrect as the gravitational pull from the earth will increase the closer you get to the center realitive to your mass!

We have drilled holes into the surface of the Earth, and nobody has reported anything that contravenes expectations with regard to gravity as we dig beneath the surface.  It is true that we have not dug very deep into the Earth, but we have some very sensitive instruments that can easily detect even the small changes of gravity that one would expect to occur as we dig a few kilometres beneath the Earth.

Furthermore, we can, on the surface of the Earth, actually detect the gravitational fields emitted by individual mountains - if all of the Earth's gravity was emanating from its centre, then we should not be able to sense any gravity emanating from surface features such as mountains.

In one respect, there might be one effect in which you have some validity, in that as you get closer to the centre of the Earth, because of the hight pressures, one would expect the density of the matter around you to increase (although the pressure will also be offset by higher temperatures, which will limit any increase in density).  More dense rock will have a greater gravitational pull, but this has to be offset by the fact that you still have more of that rock above you than below you.

In fact, as Paul has suggested, at the very centre of the Earth, the gravity from all sides will cancel out, making a nett zero gravity.  Away from the centre, there will be a gravitational pull (upwards, since all the mass of the Earth is now above you), but it will only be a very slight pull, since it is still the case that most of the gravity will be cancelled out by gravitational pull elsewhere.

I do not agree with this statement! As I feel the Earths gravity is created by more than just mass!

Would you like to provide some more detail as to what you think, aside from mass, is creating this gravity; and provide some mathematical model as to how this force would behave throughout the universe (something that can actually be tested against observation)?
 

jolly

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Gravity At The Center Of The Earth
« Reply #17 on: 07/05/2007 14:15:40 »

The gravitational pull at the centre of the Earth cannot be greater than at the surface of the Earth,

May I ask how you know that?

The same way that I know the Sun will rise tomorrow - I extrapolate from what I do know into what I do not know.  I may be wrong, maybe the Sun will not rise tomorrow, despite my experience of every previous morning when I have observed the Sun to rise, it may yet prove that my extrapolation of existing knowledge will prove to be false; but if we do not extrapolate based upon what we do know, then we are simply left with a total absence in our ability to predict anything - which serves us no good whatsoever.

Yeah what do you actually believe?


I feel that this is incorrect as the gravitational pull from the earth will increase the closer you get to the center realitive to your mass!

We have drilled holes into the surface of the Earth, and nobody has reported anything that contravenes expectations with regard to gravity as we dig beneath the surface.  It is true that we have not dug very deep into the Earth, but we have some very sensitive instruments that can easily detect even the small changes of gravity that one would expect to occur as we dig a few kilometres beneath the Earth.

My I ask how your instruments check for gravities effect?

Furthermore, we can, on the surface of the Earth, actually detect the gravitational fields emitted by individual mountains - if all of the Earth's gravity was emanating from its centre, then we should not be able to sense any gravity emanating from surface features such as mountains.

well thats a huge assumption!
Afterall mountains and volcanos are attached to the earth and esspecally in the case of volcanos- they have a direct line connection to the core and magma.


In one respect, there might be one effect in which you have some validity, in that as you get closer to the centre of the Earth, because of the hight pressures, one would expect the density of the matter around you to increase (although the pressure will also be offset by higher temperatures, which will limit any increase in density).  More dense rock will have a greater gravitational pull, but this has to be offset by the fact that you still have more of that rock above you than below you.

Well again surely in liquid form an object of big mass fills a smallier space- as there for a start will not be any air within it for example!

In fact, as Paul has suggested, at the very centre of the Earth, the gravity from all sides will cancel out, making a nett zero gravity.  Away from the centre, there will be a gravitational pull (upwards, since all the mass of the Earth is now above you), but it will only be a very slight pull, since it is still the case that most of the gravity will be cancelled out by gravitational pull elsewhere.

I do not agree with this statement! As I feel the Earths gravity is created by more than just mass!

Would you like to provide some more detail as to what you think, aside from mass, is creating this gravity; and provide some mathematical model as to how this force would behave throughout the universe (something that can actually be tested against observation)?

Sorry to be a prude but I am not prepared to discuss what I feel is the reality- with regards to Gravity.
This may upset you... but I feel that we should talk in current scientific terms and not take a new theory line!   
« Last Edit: 07/05/2007 20:03:55 by jolly »
 

Offline Bored chemist

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« Reply #18 on: 07/05/2007 15:08:20 »
Jolly, since your last "theory" about gravity ended up in the "new theories" section I think it's a bit rich for you to say "but I feel that we should talk in current scientific terms and not take a new theory line! ".
Also, our statement "I do not agree with this statement! As I feel the Earths gravity is created by more than just mass!" is, in fact an indication that you have a new theory about gravity which differs significantly from the current one scientists have been using for centuries. You are the one taking up new theories.

Also re "My I ask how your instruments check for gravities effect?"
probably like this
http://en.wikipedia.org/wiki/Gravimeter

OK, enough of "Jolly world" and back to the question.
If you were to drill a big hole thought the earth and line the "tunnel" with some magic sort of bricks that would prevent a cave in  (or, more plausibly, get a very old planet that has cooled down enough so the job gets a lot easier and drill a hole in that) then you would get a gradual reduction in the effect of gravity as you went down the tunnel to the centre of the earth then a gradual increase the other way as you went back to the surface. The variation of the force of gravity is linear with distance from the centre This result was first calculated be Newton and assumes that the density of the earth is constant- unlikely in reality but probably close enough. It also means that, neglecting air resistance, if you dropped something down the "hole" it would bounce back an to exhibiting simple harmonic motion. More importantly (at least for the purposes of this discussion), because your height is only a tiny fraction of the distance from the centre of the earth to the surface you would be pulled apart by only a tiny fraction of 1 g. The force would be something like a hundredth of a gram (OK, that should be in Newtons, but what we are talking about is the weight of a postage stamp). Even in a big "flying cave" the forces would be small so, yes Neil, you could float about like a spaceman.
 

jolly

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« Reply #19 on: 07/05/2007 15:35:36 »
Sorry Chemist, but I am not engaging with you about anything other than chemistry.....
And as I dont really care if milk stablizes me coffee- There's no need to chat.... I mean have'nt you got some water to de-gas or something?
 

Offline Bored chemist

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« Reply #20 on: 07/05/2007 16:40:41 »
Does that mean other people only have to engage with you about jollity, seems like a good idea, or is it that when you engage with me about other things you come off looking like you don't know what you are talking about?
What does "And as I dont really care if milk stablizes me coffee" mean, or are you not going to answer because it's not chemistry?
« Last Edit: 07/05/2007 16:42:14 by Bored chemist »
 

jolly

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« Reply #21 on: 07/05/2007 17:53:31 »
Not It means I am tired of listening to your comments and links relating to things you, I dont think really understand!

My post was to another someone not you!

But yet again you feel the need to come in and start posting rubbish as usual- and your probably gonna starting going on about how I'm trolling! blar blar blar!

No doubt ukmickey will be in, in a minute to close it!
« Last Edit: 07/05/2007 17:59:36 by jolly »
 

Offline Bored chemist

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« Reply #22 on: 07/05/2007 20:00:15 »
If you want to send a message to an individual like Another Someone then pm them. If you post stuff on an open forum it will be read by many and may be replied to by anyone who is logged in.
I'm sure others here will come to  their own conclusions about who is posting rubbish (like And as I dont really care if milk stablizes me coffee" and whether or not you are trolling.
BTW, why don't you think I understand gravity at least as well as you do? At least my understanding of it tallies with real life.
 

jolly

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« Reply #23 on: 07/05/2007 20:04:39 »
Whatever Bored   Anyway moving on.....


The gravitational pull at the centre of the Earth cannot be greater than at the surface of the Earth,

May I ask how you know that?

The same way that I know the Sun will rise tomorrow - I extrapolate from what I do know into what I do not know.  I may be wrong, maybe the Sun will not rise tomorrow, despite my experience of every previous morning when I have observed the Sun to rise, it may yet prove that my extrapolation of existing knowledge will prove to be false; but if we do not extrapolate based upon what we do know, then we are simply left with a total absence in our ability to predict anything - which serves us no good whatsoever.

Yeah what do you actually believe?


I feel that this is incorrect as the gravitational pull from the earth will increase the closer you get to the center realitive to your mass!

We have drilled holes into the surface of the Earth, and nobody has reported anything that contravenes expectations with regard to gravity as we dig beneath the surface.  It is true that we have not dug very deep into the Earth, but we have some very sensitive instruments that can easily detect even the small changes of gravity that one would expect to occur as we dig a few kilometres beneath the Earth.

My I ask how your instruments check for gravities effect?

Furthermore, we can, on the surface of the Earth, actually detect the gravitational fields emitted by individual mountains - if all of the Earth's gravity was emanating from its centre, then we should not be able to sense any gravity emanating from surface features such as mountains.

well thats a huge assumption!
Afterall mountains and volcanos are attached to the earth and esspecally in the case of volcanos- they have a direct line connection to the core and magma.


In one respect, there might be one effect in which you have some validity, in that as you get closer to the centre of the Earth, because of the hight pressures, one would expect the density of the matter around you to increase (although the pressure will also be offset by higher temperatures, which will limit any increase in density).  More dense rock will have a greater gravitational pull, but this has to be offset by the fact that you still have more of that rock above you than below you.

Well again surely in liquid form an object of big mass fills a smallier space- as there for a start will not be any air within it for example!

In fact, as Paul has suggested, at the very centre of the Earth, the gravity from all sides will cancel out, making a nett zero gravity.  Away from the centre, there will be a gravitational pull (upwards, since all the mass of the Earth is now above you), but it will only be a very slight pull, since it is still the case that most of the gravity will be cancelled out by gravitational pull elsewhere.

I do not agree with this statement! As I feel the Earths gravity is created by more than just mass!

Would you like to provide some more detail as to what you think, aside from mass, is creating this gravity; and provide some mathematical model as to how this force would behave throughout the universe (something that can actually be tested against observation)?

Sorry to be a prude but I am not prepared to discuss what I feel is the reality- with regards to Gravity.
This may upset you... but I feel that we should talk in current scientific terms and not take a new theory line!   
« Last Edit: 08/05/2007 13:21:49 by jolly »
 

Offline JimBob

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« Reply #24 on: 08/05/2007 02:42:43 »
Ignore this person when he/she/it starts "trolling."
 

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« Reply #24 on: 08/05/2007 02:42:43 »

 

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