I don't understand why there is such a thing as a parabola or hyperbola. Halley's comet travels in an ellipse that isn't symmetrical (I think). Do any objects that travel in a parabola pass by the earth, using the earth to swing back out into space? Can you give me an example of when a parabola or hyperbola exists?

Well,
as far as I know

hypothetically

when a ball is thrown upwards
it moves with a certain velocity, horizontally aswell as vertically each.
The force acting on the ball vertically, i.e. gravitational force, is constant. Whereas, due to conservation of Energy
the horizontal motion lost initially
(till the time comes when v=0) is gained back at the same pace after this point.
Thus, resulting in a symmetrical path (in this case, a parabolla)

HOWEVER, this is 'hypoethetical' the friction and drag present don't allow the path to be exactly symmetrical.

Pin~Jinx /anarchist

If I understand the question correctly, whether the orbit of a satellite around the earth is an ellipse, parabola, or hyperbola depends on the velocity it has and the distance from the earth. A satellite orbits the earth in a nearly circular orbit if it has a velocity of about 5 miles per second. (18,000 mil;es per hour), and at an altitude of about 400 miles. The greater the velocity, the more elliptical the orbit. At a velocity equal to the escape velocity, the orbit becomes parabolic, and at a velocity greater than the escape velocity it assumes a hyperbolic orbit. I shouldn't say orbit, I guess because in either case it does not return to earth. It would, however, assume an orbit around the sun unless its velocity were sufficiently high as to exceed the escape velocity of the sun. I'm sure you know that either an hyperbola or a parabola is an open curve. So it would seem to me that an earth satellite that assumes a parabolic or hyperbolic flight path could acquire a circular or elliptical one about the sun, for instance. Now, I'll just wait until the astronomy experts shoot me down in flames.

I'm not an astronomer either, but I believe Frank's answer to be 100 percent correct. A satellite traveling above earth's escape velocity at a given altitude will take a hyperbolic 'orbit' around the earth, never to return, but , like the Helios satellite traveling at 160,000 mph, may go into elliptical orbit around the sun, as long as its speed is above the escape velocity of the sun at it's altitude. And while periodic comets such as Halley's are in elliptical orbit around the sun, other comets are in hyperbolic orbit around it, passing by the sun just once, then moving on forever away from it, heading perhaps for the nearest black hole.:).)

What is the difference between a parabola and a hyperbola? I love this ieSpell checker. I know Jerry why you don't know how to use a spell checker. YOU KNOW HOW TO SPELL!!! Also, I'm guessing that the minor axis of a comet is symmetrical. But that the major axis is not.

tv

I had an argument with my Physics teacher about the path taken by a thrown object. He'd used the textbook answer, that it was a parabola. I pointed out that the textbook proof had a flaw in it - it assumed that the lines of gravitational force were parallel, whereas in fact they meet at the earth's centre. We did a class exercise, and proved that the true answer really is an ellipse, though the deviation from a parabolic path is negligible. (I was an unbearable smartass in those days...)