• Lucid Dreaming - Dream Views




    Page 1 of 2 1 2 LastLast
    Results 1 to 25 of 30
    Like Tree7Likes

    Thread: Gravity in The Core of The Planet

    1. #1
      Ex Tech Admin Achievements:
      Created Dream Journal Tagger First Class Veteran First Class 10000 Hall Points Populated Wall Referrer Gold Made lots of Friends on DV
      slash112's Avatar
      Join Date
      Nov 2008
      Gender
      Location
      Sunny Scotland
      Posts
      5,113
      Likes
      1563
      DJ Entries
      29

      Gravity in The Core of The Planet

      So uhh, yea, earlier on today, I was wondering about what happens to the size of the force of gravity as you get closer to the core.

      Apparently it is accepted that the force grows stronger as you get closer to the core.

      But, is it not true that gravitational force is dependant on the size of mass?

      If that is the case, then how come as you get to the core, the gravitational field increases?


      Take this for example (Hypothetically, of course):
      You make an elevator which brings you right down to the core.
      As you near the bottom, there will be less mass beneath you, therefore the gravitational force pulling from below will be weaker, and the force pulling from above will get stronger (Which means of course, the total force will be weaker).

      Now, if you were to be right in the very middle of the planet, wouldn't you be sort of being pulled out the way in every direction? This would equal a total force of zero. Even though going by the whole "stronger as you get closer" theory, it should be stronger than it is on the surface.


      So... is this not true, then?
      If not, then care to explain why?

      I have always been fascinated by gravity, I just haven't looked into it as much as this. I also googled for a little while and didn't really find anything about this.
      So either I never googled very well, or it is just bullshit enough to not have been talked about before. I dunno. But I am very curious.

    2. #2
      Banned
      Join Date
      Apr 2007
      Location
      Out Chasing Rabbits
      Posts
      15,193
      Likes
      929
      No, mathematically, gravity is 0 in the centre of a sphere, where did you get the idea that the centre of the earth would have stronger gravity?

    3. #3
      Flailing chicken barnacle Achievements:
      Created Dream Journal Made lots of Friends on DV Populated Wall Tagger First Class 1000 Hall Points Veteran First Class
      Indeed's Avatar
      Join Date
      Mar 2010
      LD Count
      10
      Gender
      Location
      Earth
      Posts
      567
      Likes
      118
      DJ Entries
      15
      Perhaps there would be slight gravity facing outwards.
      Alex is greatest. He <i>is</i> the Master Flan.

    4. #4
      Retired Post Whore-73PPD jarrhead's Avatar
      Join Date
      Jan 2010
      LD Count
      82
      Gender
      Location
      Tijeras/Albuquerque
      Posts
      1,938
      Likes
      122
      DJ Entries
      24
      The gravity does get lighter if I remember correctly, BUT, you will have the pressure of hundreds of miles of rock above you.

    5. #5
      Ex Tech Admin Achievements:
      Created Dream Journal Tagger First Class Veteran First Class 10000 Hall Points Populated Wall Referrer Gold Made lots of Friends on DV
      slash112's Avatar
      Join Date
      Nov 2008
      Gender
      Location
      Sunny Scotland
      Posts
      5,113
      Likes
      1563
      DJ Entries
      29
      Quote Originally Posted by ninja9578 View Post
      No, mathematically, gravity is 0 in the centre of a sphere, where did you get the idea that the centre of the earth would have stronger gravity?
      Cause when I googled it, it said "It is accepted that as you go closer to the core of the earth, the gravitational force increases" or something along those lines.

    6. #6
      Banned
      Join Date
      Apr 2007
      Location
      Out Chasing Rabbits
      Posts
      15,193
      Likes
      929
      No, because the more rock you have above you, the more it cancels out the rock below you. Gravity at the centre of a ring or a sphere is 0, always.

      Perhaps they are getting confused by the fact that you get closer to the centre of gravity, the strength of it increases, but that doesn't apply if you are inside of the object

      And jarhead is correct, the reason the centre of the earth is molten is because of pressure, not gravity.

    7. #7
      Ex Tech Admin Achievements:
      Created Dream Journal Tagger First Class Veteran First Class 10000 Hall Points Populated Wall Referrer Gold Made lots of Friends on DV
      slash112's Avatar
      Join Date
      Nov 2008
      Gender
      Location
      Sunny Scotland
      Posts
      5,113
      Likes
      1563
      DJ Entries
      29
      Everything you said there is what I assumed was true before I googled it.

      Thanks. *shakes fist at google*

      ...ok I probably read it wrong.

    8. #8
      Xei
      UnitedKingdom Xei is offline
      Banned
      Join Date
      Aug 2005
      Posts
      9,984
      Likes
      3082
      Take this for example (Hypothetically, of course):
      You make an elevator which brings you right down to the core.
      As you near the bottom, there will be less mass beneath you, therefore the gravitational force pulling from below will be weaker, and the force pulling from above will get stronger (Which means of course, the total force will be weaker).

      Now, if you were to be right in the very middle of the planet, wouldn't you be sort of being pulled out the way in every direction? This would equal a total force of zero. Even though going by the whole "stronger as you get closer" theory, it should be stronger than it is on the surface.
      You are exactly right Slash.

      At any point above the surface of the Earth, you can model the gravity using a single point at the centre of the planet, with the mass of the planet (i.e. the inverse square law applies).

      However below the surface it gets a lot more complicated and you have to use various integrals to work it out (except at the centre where it's clearly 0 and you would float about as if in outer space). The best way to think about it, as you have done, is to consider in which direction each individual atom is pulling you.
      And jarhead is correct, the reason the centre of the earth is molten is because of pressure, not gravity.
      Well, gravity is what causes the pressure... also, pressure actually raises the melting point of the rock. The centre of the Earth is molten because the centre of the Earth is very hot. I think this is partly due to the residual energy from the huge amount of energy created in the formation of the Earth, and also I think uranium decay is involved.
      JoshNtrepid likes this.

    9. #9
      Retired Post Whore-73PPD jarrhead's Avatar
      Join Date
      Jan 2010
      LD Count
      82
      Gender
      Location
      Tijeras/Albuquerque
      Posts
      1,938
      Likes
      122
      DJ Entries
      24
      The centre of the earth is solid. The outer core, however is molten, but the inner core is still solid.
      JoshNtrepid likes this.

    10. #10
      Xei
      UnitedKingdom Xei is offline
      Banned
      Join Date
      Aug 2005
      Posts
      9,984
      Likes
      3082
      True, true. I was being sloppy, by centre I meant core.
      JoshNtrepid likes this.

    11. #11
      Retired Post Whore-73PPD jarrhead's Avatar
      Join Date
      Jan 2010
      LD Count
      82
      Gender
      Location
      Tijeras/Albuquerque
      Posts
      1,938
      Likes
      122
      DJ Entries
      24
      Inner core's still solid and if I remember correctly, 10,000 - 15,000 degrees. I don't remember if that's Celsius of Fahrenheit -- probably Fahrenheit

    12. #12
      Member
      Join Date
      Feb 2004
      Posts
      5,165
      Likes
      709
      Can't believe everything you read on the internet. You probably read it correctly, and it was just wrong. Luckily you were thinking about what you were reading, instead of just accepting everything as fact.

    13. #13
      Member
      Join Date
      Jul 2007
      Posts
      528
      Likes
      16
      Because the material is denser near the centre of the earth, as you approach the core gravity does get stronger, until about 1/2 the way the core, there the gravity is strongest, but from there gravity gets weaker until it eventually becomes 0 at the core.

      This diagram illustrates
      http://en.wikipedia.org/wiki/File:Earth-G-force.png
      JoshNtrepid likes this.

    14. #14
      A Natural The Invisible Man's Avatar
      Join Date
      Nov 2008
      Gender
      Posts
      365
      Likes
      8
      I can totally understand why someone would believe that the force of gravity increases as one approaches the center of the mass. We actually have a formula in Physics that describes the force of gravity between two objects. Better yet, it's dependent on the distance between the two masses as well, where the decreased distance actually increases the force.

      But, everyone else is quite right. When you're underneath the Earth, there's mass on top of you as well that pulls and cancels what pulls from below.


      Can you see me now?

    15. #15
      Moo nsi dem oons ide kookyinc's Avatar
      Join Date
      Jun 2010
      LD Count
      4
      Gender
      Location
      Moonside
      Posts
      529
      Likes
      118
      DJ Entries
      16
      Are we assuming that this planet is a perfect sphere with a consistent density? In that case, if teleported to the center of the planet, one would probably feel gravity pulling the person apart in all directions. However, few, if any, planets are perfect spheres with consistent densities, though.
      I don't usually think, therefore I mostly am not.
      Quote Originally Posted by abicus View Post
      You can not convince the one with faith who needs not look for fact that the facts "prove them wrong".
      Likewise, you cant teach some one who looks for facts to have faith in the absence of facts.

    16. #16
      Xei
      UnitedKingdom Xei is offline
      Banned
      Join Date
      Aug 2005
      Posts
      9,984
      Likes
      3082
      You wouldn't feel any force. Just consider each atom in your body. How can they be pulled apart in all directions? How would each individual atom move? The key point is that it's the sum of all the forces which counts, and at the centre of the Earth, they sum to the 0 vector. None of the atoms in your body would move anywhere, so you wouldn't feel anything. It'd just feel like falling, without the wind.
      JoshNtrepid likes this.

    17. #17
      Hungry Dannon Oneironaut's Avatar
      Join Date
      May 2008
      Gender
      Location
      Dreamtime, Bardos
      Posts
      2,288
      Likes
      808
      DJ Entries
      5
      So, with no gravity, there would be no pressure, right? If you fell down the elevator shaft would you fall all the way to the center? Or would you slow down until you started floating? Would you fall back up to the halfway point? Like bungee jumping? I always assumed that it was the center of the mass that was the center of gravity. But of course there couldn't be any gravity because there is no more 'down' to fall. Just like at the north pole you can't go in any other direction except south. At the center of the Earth all directions are up.
      JoshNtrepid likes this.

    18. #18
      Member Achievements:
      Made Friends on DV 1000 Hall Points Veteran First Class

      Join Date
      Jun 2010
      Gender
      Posts
      708
      Likes
      348
      Pressure, density, and gravity are all related on a deep level. This is inclusive of time as well. Basically, pressure can be seen as a scalar quantity dependent on the acting normal force maintained from the surface of the earth. With depth comes density comes an increase in gravity; thusly pressure, and in turn a change in the passage of time relative to an observer from some arbitrary distance with other conditions, but that's not very relevant. Anyway, the pressure one would experience at the center of the earth would be appreciable - about 3.5 megabar - however, gravity itself would diminish at some relation, as others have said, due to the surrounding mass in all directions causing a null, or zero, resultant vector. Even with a perfect cylindrical tube cut to the center of the earth, which could never happen, the air pressure alone would be enough to obliterate any human or human-made device long before it reached the center.
      Last edited by Phion; 06-22-2010 at 04:48 AM.

    19. #19
      Xei
      UnitedKingdom Xei is offline
      Banned
      Join Date
      Aug 2005
      Posts
      9,984
      Likes
      3082
      Interesting. It's weird to think such high pressures could exist at the centre of the Earth where there's no gravity. I suppose this is because the atmosphere above and below you is acting like a heavy cork, keeping the local atmosphere around you squashed in.
      Quote Originally Posted by Dannon Oneironaut View Post
      So, with no gravity, there would be no pressure, right? If you fell down the elevator shaft would you fall all the way to the center? Or would you slow down until you started floating? Would you fall back up to the halfway point? Like bungee jumping? I always assumed that it was the center of the mass that was the center of gravity. But of course there couldn't be any gravity because there is no more 'down' to fall. Just like at the north pole you can't go in any other direction except south. At the center of the Earth all directions are up.
      Yes, that's a good way to think about it ('by symmetry').

      If there were no air in the tunnel, you would accelerate towards the centre (to a very large speed), then keep going whilst decelerating, until you came back outside the other side to ground level, and then you would fall back again.

      If there were air, air resistance would mean you would only overshoot the centre a tiny bit, and then pretty quickly come to rest at the centre.

    20. #20
      Hungry Dannon Oneironaut's Avatar
      Join Date
      May 2008
      Gender
      Location
      Dreamtime, Bardos
      Posts
      2,288
      Likes
      808
      DJ Entries
      5
      So there could be no Zion from the Matrix.

    21. #21
      Xei
      UnitedKingdom Xei is offline
      Banned
      Join Date
      Aug 2005
      Posts
      9,984
      Likes
      3082
      ...that was underground, in the sewers. Not the centre of the Earth.

    22. #22
      Member really's Avatar
      Join Date
      Sep 2006
      Gender
      Posts
      2,676
      Likes
      54
      Quote Originally Posted by Xei View Post
      ...that was underground, in the sewers. Not the centre of the Earth.
      Could there be a 'The Core'? Haha, probably not.

      What can you guys say about the core of the earth actually rotating at a different speed to the Earth?

    23. #23
      Member
      Join Date
      Mar 2010
      Location
      Where ever
      Posts
      365
      Likes
      27
      Maybe there is a mini-stabilized blackhole at the center of the Earth? dun dun dun...

    24. #24
      Hungry Dannon Oneironaut's Avatar
      Join Date
      May 2008
      Gender
      Location
      Dreamtime, Bardos
      Posts
      2,288
      Likes
      808
      DJ Entries
      5
      Quote Originally Posted by Xei View Post
      ...that was underground, in the sewers. Not the centre of the Earth.
      I just watched The Matrix again the other night and they said that Zion was near the core. And if I remember correctly, in the last movie the sentinels had to borrow for days through solid rock to reach it.

    25. #25
      Member
      Join Date
      Mar 2010
      Location
      Where ever
      Posts
      365
      Likes
      27
      Quote Originally Posted by really View Post
      Could there be a 'The Core'? Haha, probably not.

      What can you guys say about the core of the earth actually rotating at a different speed to the Earth?
      Actually, it may. Probably depends on how dense it is. If it isn't that dense, then is probably rotates faster than the rest of the Earth to make up for it, which it creates torque as a multiplier force.

    Page 1 of 2 1 2 LastLast

    Similar Threads

    1. Starting Everyman (4.5 hr core + 2 naps)
      By The Subatomic Level in forum Sleep and Health
      Replies: 14
      Last Post: 01-07-2015, 05:35 AM
    2. Movies Like Planet of the Apes 2: Beneth the Planet of the Apes
      By Reality_is_a_Dream in forum Entertainment
      Replies: 5
      Last Post: 10-16-2008, 10:37 PM
    3. The core.
      By Lucid_boy in forum Religion/Spirituality
      Replies: 7
      Last Post: 11-09-2007, 01:17 AM
    4. The imminent core-breach of my Gravity Drive
      By Izinyo in forum Dream Journal Archive
      Replies: 32
      Last Post: 12-04-2005, 07:19 PM
    5. Riddle me THIS! (philosophy at its core)
      By insanejester in forum Philosophy
      Replies: 22
      Last Post: 08-11-2004, 08:22 PM

    Bookmarks

    Posting Permissions

    • You may not post new threads
    • You may not post replies
    • You may not post attachments
    • You may not edit your posts
    •