Winnipesaukee from space

[DickR]

Originally Posted by Slickcraft

Well sort of free falling but countered by centripetal force. In classical Newtonian physics when the speed related centripetal force equals the gravitation force then a stable circular orbit is achieved.

Well, not quite. There is gravitational attraction between earth and satellite. The centripetal force is the earth's pull on the satellite, and the centrifugal force is the satellite 's pull on the earth (equal and opposite). It's when the satellite has a velocity at right angles to that force such that F=M*V^2/R that the orbit is circular. With the velocity always at right angles to the gravitational pull, there is no component of that force along the direction of motion, so the satellite's speed is undiminished (except by by friction with the few molecules of air up that high).

Imagine a tower 100 miles tall. At the top you throw a rock sideways at modest speed. The rock falls in a curved arc, getting steeper as gravity pulls the rock down. If you fire the rock out from a cannon, the rock lands farther out from the base of the tower. With the arm of Superman pitching the rock faster and faster each time, the curved arc the rock follows gets closer and closer to matching the curvature of the earth, until finally that magic speed is applied at which the match is perfect and the orbit is circular. At that point, the rock essentially is "falling around the earth."

When the satellite is given a velocity greater than is needed for a circular orbit at that altitude, but less than "escape velocity," the orbit becomes elliptical. The speed decreases with distance from earth, then increases again as it returns to the closest point. If the initial velocity is less than needed for orbit at that altitude, the curved path is tighter than the curvature of the earth's surface, and the satellite never achieves orbit.

Ummm, more than you wanted to know, I guess, but I couldn't help it. Now help me here. In the photo I don't see the state lines. Are they too narrow to show from that height?