NOTES
Ringworld might at first seem like an ideal frictionless oscillator – it’s in a vacuum after all, and it’s made out of material that doesn’t distort (except under very extreme circumstances). However, the material on the Ring is not so ideal, so the solar tides that lead to the “hump” in the middle would result in forces that would tend to move the material on the Ring over the course of the seasonal oscillation, leading to friction, and dramatic effects like rivers that flow in different directions depending on the time of year.
The friction would tend to damp out the oscillation of the Ring, so Ringworld seasons would not be automatic – there would have to be a driving force continually adding energy to the oscillation to keep it going, and you’d have to be willing to tolerate the other strange effects, like oscillating rivers.