I know that gravity keeps us on the earth, but what prevents us from being pushed or pulled through the floor, earth, etc. (besides concrete, wood, and soil)? Does it have something to do with opposite forces?
Asked by: Karen
In a nut shell, the answer is the electromagnetic field.
Until the beginning of this century, there were only two known force fields -- gravity and
the electromagnetic (EM) field. The strong and weak nuclear fields were not known. The
electromagnetic field manifests itself in many different ways. The force between magnets
is a manifestation of the magnetic aspect of the EM field. The force that attracts your
hair when you comb it in winter is a manifestation of the electric aspect of the EM field.
Light, radio waves, gamma rays, etc. are manifestations of the simultaneous combination of
alternating magnetic and electric fields. James Clerk Maxwell, in his famous 'Maxwell's
equations' provided a proper mathematical basis for understanding the unification of the
magnetic and electric aspects of the EM field.
When two ordinary objects, such as your shoes and the floor on which you stand, come close
enough together, the electrons that surround the atoms of the floor and of your shoes
repel each other strongly through the electic force (the so-called Coulomb force).
Specifically, electrons in your shoes and in the floor strongly repel each other because they
carry like (by convention, 'negative') electric charges, which are responsible for creating
similar electric fields around each electron. The force of repulsion is mediated by the
electric fields established by the charges on the electrons.
The magnitude of this force increases inversely as the distance between the sources of the
field, the electrons. Hence, the electric forces can quickly become very great, even great
enough to support the weight of your body against the attractive force of the other
significant field -- gravity.
Because of the repulsive force of the electic field of the electrons, the nuclei of atoms
do not come close enough to each other under ordinary circumstances for the effects of the
two nuclear forces to be observable. Exceptions are in the interior of a star, a
thermonuclear (H-bomb) explosion, and in the plasma in a Tokomak used to generate energy by
As you suggest, opposite forces are involved. But, not a force opposite to gravity. Rather,
it is the opposite, or repulsive, force between like electric charges that reside in concrete,
wood, soil, etc. that supports you against gravity, and, indeed, that enables us to interact
with all ordinary objects in our environment.
Answered by: Warren Davis, Ph.D., President, Davis Associates, Inc., Newton, MA USA
'I believe there is no philosophical high-road in science, with epistemological signposts. No, we are in a jungle and find our way by trial and error, building our road behind us as we proceed.'