Most elementary particles (like electrons and
quarks) have an intrinsic property called
spin which, when on charged particles
(again like electrons and quarks) produces a
magnetic field. However, this field is usually
very weak, since the orientations of many such
particles cancel each-other out. The earth has a
magnetic field created by convection currents in
the outer core, which is made of molten iron (plus
a few other elements as well). Any particle in
this field will experience its very slight
magnetic field, but it is so weak that it is
difficult to notice without a fairly sophisticated
measuring device like a compass made out of
material that is easily magnetized (like iron).
For example, you do not notice when you are
facing North, South, East, or West, because the
effect of the earth's magnetic field on the
particles that make up your body is minuscule. You
are not made up of easily magnetizable material.
There are animals that do have sense organs
that are magnetized and can sense magnetic
fields, such as some whales, but humans are
not among them.
There are some neutron stars (called
magnetars) that do have magnetic fields so
powerful they would tear you apart if you got
close due to the diamagnetic effects of the fields
on the water in your body. However, the earth's
effects are so minor that it doesn't matter.
The only meaningful force you experience from
the earth is gravity.
Not every atom is affected by the earth's magnetic
field. Whether or not an atom is affected depends
on how its "electron configuration (how
many electrons is has, and how they are
distributed in the atom). Let's take an element
whose atoms are affected by the magnetic field,
for example, iron (Fe). No matter where on
Earth you put an atom of iron, it will be vaguely
affected by the earth's magnetic field. This is
because the earth's magnetic field is equally
strong all over the globe. We take advantage of
this when we use a compass to navigate -- you can
use a compass anywhere on the earth and it will
always point North.
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