Space Craft and Gravity
how can gravity be overcome?
By definition you must exceed the escape velocity in order to leave earth orbit
(if this is what you are interested in). The escape velocity is a function of
the distance from the earth so if you choose you can keep applying lift (always
just barely greater than the gravitational force) and you would eventually
escape from the earth without ever achieving a large velocity. However, you
have now applied a somewhat smaller force for a much longer period of time.
This would not be energy efficient.
To experience gravitational pull is equivalent to the facts of
having mass and being near another mass. Hence what you need to do is
remove one or the other fact. If you destroy the Earth, your
spacecraft will no longer be pulled toward it. But of course it will
be pulled toward other bodies, so, to be on the safe side, you should
destroy your spacecraft. It will then be free of any gravitational
Your question is not unlike the question of: how can I travel in
time so that I can become my own grandfather? in the sense that the
question itself, with all terms given their proper physical meaning,
is logically inconsistent. The existence of mass is proven by its
response to gravity. That is, when a region of space does not respond
to gravity, it contains no mass, by definition.
Actually, it isn't really necessary to achieve the escape velocity from the
surface of the earth. Escape velocity means that you have enough kinetic
energy to escape the earth's gravitational field; in a rocket flight, the
engine burns over a period of time, constantly applying kinetic energy to
the craft until it has enough to get where it needs to go. Once you are in
orbit, escape velocity is much less than from the surface. So, escape from
the earth CAN be done at any speed, but it takes a whole lot of energy no
matter how fast or slow you go.
As far as cheating gravity is concerned, we don't know of anyting that can
do this. The problem is that gravity is purely an attractive force;
everything with mass has a gravitational field that interacts with
everything else that has mass. We haven't found anything that screens or
neutralizes a gravitational field.
Richard Barrans Jr., Ph.D.
You cannot shield gravity. Under typical conditions in the universe the
force is always there between two or more objects.
Jules Verne suggests other ideas but that is pure fiction. Check out any
Conceptual Phyics textbook (Gravitational Force) by Paul Hewett
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Update: June 2012