"Donald G. Shead" wrote in message m...
An orbit is the balance between two compensating motions: Impetus, or
momentum, and centripetal free fall. That is, the earth is continually
falling toward the sun, but its impetus keeps it moving in an ellipse. When
these two motions are at a sufficiently oblique angle to each other a stable
orbit results.

........
This is an extremely simplistic view which does not lead to an
understanding of orbital motion.
An object in orbit is only falling for half of the orbit. In the other
half of the ellipse it's velocity is above the acceleration of
gravity. A person can jump, momentarily exceeding the acceleration of
gravity.

An orbit with momentum that equals the acceleration of gravity is a
parabola.
Consider a comet from beyond the solar system. If the velocity of the
comet is too great, it turns at the sun and has escape velocity. It's
curve is a hyperbola and it does not return to the sun. The
theoretical amount of energy that defines the difference of orbits
from hyperbola and ellipse is the parabola. A parabola is x=y squared.
Momentum is a single vector. Gravity is an acceleration or seconds
squared. Gravity continually increases velocity of a falling object.

In an orbit the single vector of the momentum can never equal the
acceleration of gravity to form a circular orbit. The velocity is
always decreasing or increasing. The force of gravity changes as an
inverse square to distance. Escape velocity is the speed required so
that with gravity acting on the object through time, with the distance
increasing and diminshing the force of gravity, the object has
velocity away from the scource of the gravity remaining. The energy of
an orbit can be defined as a unit. Orbits with equal energy have equal
area despite eccentricity.

http://home.earthlink.net/~kdthrge

"kdthrge" wrote in message
om...
"Donald G. Shead" wrote in message
m...
An orbit is the balance between two compensating motions: Impetus, or
momentum, and centripetal free fall. That is, the earth is continually
falling toward the sun, but its impetus keeps it moving in an ellipse.
When
these two motions are at a sufficiently oblique angle to each other a
stable
orbit results.

.......
This is an extremely simplistic view which does not lead to an
understanding of orbital motion.

Yes it is; but what can be better than a simple view to illustrate orbital
motion: Certainly what you say below does not make it more understanding.

An object in orbit is only falling for half of the orbit. In the other
half of the ellipse it's velocity is above the acceleration of
gravity. A person can jump, momentarily exceeding the acceleration of
gravity.

An orbit with momentum that equals the acceleration of gravity is a
parabola.
Consider a comet from beyond the solar system. If the velocity of the
comet is too great, it turns at the sun and has escape velocity. It's
curve is a hyperbola and it does not return to the sun. The
theoretical amount of energy that defines the difference of orbits
from hyperbola and ellipse is the parabola. A parabola is x=y squared.
Momentum is a single vector. Gravity is an acceleration or seconds
squared. Gravity continually increases velocity of a falling object.

In an orbit the single vector of the momentum can never equal the
acceleration of gravity to form a circular orbit. The velocity is
always decreasing or increasing. The force of gravity changes as an
inverse square to distance. Escape velocity is the speed required so
that with gravity acting on the object through time, with the distance
increasing and diminshing the force of gravity, the object has
velocity away from the scource of the gravity remaining. The energy of
an orbit can be defined as a unit. Orbits with equal energy have equal
area despite eccentricity.

http://home.earthlink.net/~kdthrge

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