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## Summary:

- Using Newton's Universal Law of Gravity to prove an elliptical orbit.

## Main Question or Discussion Point

When proving that Newton's Universal Law of Gravity will produce an elliptical orbit, the radial acceleration is confusing to me. Can someone please explain how the radial acceleration is equal to d^2/dt^2 - r(d x theta / dt)^2. Could someone please detail how that acceleration is derived? Thank you. Here is a link to the proof http://farside.ph.utexas.edu/teaching/301/lectures/node155.html