 |
 |
Pressure and Gravitational Field at Earth's Center
Name: Bob
Status: student
Age: N/A
Location: N/A
Country: N/A
Date: N/A
Question:
Regarding pressure at the center of the earth,
http://www.newton.dep.anl.gov/askasci/env99/env002.htm
it seems that the comments by Argonne reviewers that gravity is zero
or near zero and that things would float contradicts statements that
the pressure is high. If you consider a spherical surface at the
center, all the material on the outside of the surface is under no
force, i.e., it is floating in a zero gravity field. Therefore the
force on any material at the surface is also near zero--in other
words no pressure. I would guess that at the maximum estimated
temperature at the center, even iron would be a solid, if the
pressure estimates of 380 Gpsl's were correct. From seismic surveys
it appears the center is in a liquid state which is consistent with
iron at 2000 degrees C at a relatively low pressure. What is the
model used to calculate the pressure at the center?
Replies:
The force due to gravity is definitely not zero at the center of the
earth. You would feel like you were floating because the forces of
gravity working on you body from every direction would be balanced.
Its a bit like those globes you see for sale in airline magazines and
elsewhere that are suspended in air by some magnets in the base and in
an overhead arm. The globe is experiencing magnetic force that cancels
out the effect gravity and is floating but surely gravity is still
around. Just remove the magnets..
As far as the condition of the center of the earth, there seem to be
two separate cores, quite creatively named the inner and outer. The
outer core is a material that "acts like a liquid in that it will not
transmit shear or transverse waves". As to what it looks like, the only
thing we can say is that you probably could not pour it. At those
temperatures and pressures the words solid and liquid really have a very
different meaning.
The inner core does support shear waves and so acts like a solid.
As we cannot generate nearly the temperatures and pressures of the inner
and outer core on earth's surface for more than a few milliseconds at a
time , the best we can do is some very sophisticated modeling of how
materials would react to those conditions.
Robert Avakian
Click here to return to the Physics Archives
| |
Update: June 2012
|
|
