posted on Oct, 8 2010 @ 12:25 PM
reply to post by tauristercus
You are observing that the gravitational force on a freely moving body (with no other force acting on it) is exactly balanced by the force with which
its inertia resists acceleration (change in direction or magnitude of velocity.) This force is called the centrifugal force when discussing rotating
objects. It is balanced by the centripetal force of gravity in the case of a freely orbiting object in a vacuum.
I am confident that your results would work fine for elliptical orbits or even for complex multi-body orbits (though we don't know how to write
simple equations for the multi-body problem.)
It even works to compute the partial component of the total forces on a body due to centrifugal force of objects subject to other forces, such as the
force of my chair on my backside as I sit here, or the force of a rocket engine firing.
Every force is balanced by an equal and opposite force. After netting out any other forces (the chair pressure or rocket engine firing) then the
force of gravity is balanced by the equal and opposite force that is an objects inertia ... its mass times whatever acceleration it is undergoing.
BUT you still need to consider gravity. Let's say that the earth suddenly became much lighter. Say the aliens come along in an enormous starship
and shoot a massive laser beam right at earth, causing HALF of the entire earth's mass to shoot out the other side in a plasma beam, creating a
gigantic hole in our planet. We would still have our nice planet; it just has this little problem -- a BIG HOLE in it.
What would happen next?
Earth's gravitational pull would weaken by half. Orbiting satellites would rise to higher orbits. The atmosphere would rise higher and become less
dense. I would weigh what I weighed in my youth, long ago.
Other things would occur as well, such as earthquakes, volcanoes, and a spike in posts on ATS announcing the sighting of aliens, with replies
But the force of earth's gravity cannot be ignored when computing the orbit of a satellite. So long as earth's mass (hence it's gravitational
pull) remains constant (no alien laser beams) then the force of gravity BALANCES the centrifugal force of a satellite constantly accelerating (moving
out of a straight line) in orbit. But as soon as the earth's mass changes (that big alien laser zap) then the earth's mass changes, hence its
gravitational field changes, hence that satellite's orbit changes.