alleryStart learning →Under what condition does an ellipse become a circle?
AWhen its two foci lie far apart
BWhen one focus leaves the curve
CWhen it is viewed from an angle
DWhen its two foci coincide
Answer & Solution
Correct answer: D. When its two foci coincide
1. An ellipse is drawn about two fixed points called foci.
2. Bring those two foci together at a single point and the curve becomes a circle.
3. Every point on that circle is then the same distance from the shared centre.
4. So a circular orbit is simply the special case of Kepler's elliptical orbit.
_Source: OpenStax College Physics (CC BY 4.0), Ch 6 "Uniform Circular Motion and Gravitation", section Kepler's Laws of Planetary Motion_
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