No force is necessary to cause orbital motion.
The planets orbit the sun (( roughly the center
of the effective mass (M-m) of the rest of the
universe )) at a special mean orbital radius to
conserve total energy
Every orbiting mass m has kinetic energy due
to its velocity v as mv^2 and potential energy
due to its radius of curvature L,
as G ( M-m) m / L , consistent with the first
law of thermodynamics, which states that the
total energy of the universe is a constant. The
sum of kinetic and potential energies of any
orbiting mass m is a constant.

SEE BOOK:
ONE WITH THE UNIVERSE-
THE MECHANICS OF
THE UNIVERSE
by Allen C. Goodrich

SEE: ISBN 0-595-41598-9


THE MECHANICS OF
THE UNIVERSE

Copyright 1984-2007 Allen C. Goodrich

SIR ISAAC NEWTON (1642 - 1727 )is best
known for his laws of motion and his
proposition of a universal gravitation theory,
which states that all bodies in space and on
the earth are affected by a force called
gravity.
However, we now know that orbital motion
has nothing to do with a force of gravity.
I have found that orbital motion obeys the
modified first law of thermodynamics. which
states that the total energy of the universe is a
constant. The total energy of a planet or moon
is a constant, because there is no known way
for its energy to be changed except by
radiation of energy or contact with another
mass.
Orbiting masses have kinetic and potential
energies that are nearly equal, because
orbital motion occurs at the only orbital radius
where a positive change of kinetic energy is
accompanied by an equal negative change of
potential energy, complying with the modified
first law of thermodynamics.
All of the planets and moons orbit in a
manner that is consistent with the modified
first law of thermodynamics.
Any orbiting mass, m , such as the earth,
has a kinetic energy m (2 pi L )^2 / t^2
because of its velocity ,v , as m v^2 , and
a potential energy G ( M-m ) m / L,
because of its orbital radius L and the product
of the masses m and the rest of the effective
mass of the universe M-m, where M is the
effective mass of the total universe. In the
solar system this mass M would effectively
be the sum of the masses of the sun and
the rest of the masses of the planets and
moons of the solar system.
The sum of kinetic and potential energies
would be a constant for any particular planet,
or moon , because , no force, as a source
of an energy change, is available to the
orbiting mass ( if it is not in contact with another
mass ) . As a result, it continues to orbit at
nearly the same radial distance from the
center of the mass of the rest of the effective
universe, complying with the modified first law
of thermodynamics, as the fundamental
equation of the universe.