Elliptical Orbits

Why revolving bodies have their orbits elliptical and not perfectly circular (please correct me if I am wrong)?

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A.T.
Why revolving bodies have their orbits elliptical and not perfectly circular (please correct me if I am wrong)?
Is there anything in nature that is perfectly circular? Perfect circles exist in math only.

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Because ellipses (technically, conic sections) are the trajectories of particles in a 1/r potential. If gravity had a different relation of force vs. distance, there would be different shaped orbits.

Because ellipses (technically, conic sections) are the trajectories of particles in a 1/r potential. If gravity had a different relation of force vs. distance, there would be different shaped orbits.
Just for a comparison, and I actually wonder about it: Celestial bodies revolve around other objects due to gravity, does the same apply to Saturn's rings too (or is it just like Saturn's atmosphere)?

I was looking for an example for a circular orbit. Saturn's rings are a set of large number of bodies and they together form a perfect circular orbit.

If a satellite were in a circular orbit, but then it gets knocked by a meteoroid so that the direction of its tangential velocity is no longer exactly perpendicular to the direction of the gravitational force, that would make the orbit become elliptical.

A.T.