Home › AP Physics 1 › Physics › Uniform Circular Motion and Gravitation › Kepler's first law describes the shape of a plan…
Kepler's first law describes the shape of a planet's orbit around the Sun. What shape does it state, and where does the Sun sit within it?
AA perfect circle, with the Sun at its exact center
BA parabola, with the Sun at its vertex
CAn ellipse, with the Sun at one focus
DA spiral, with the Sun at its innermost point
Answer & Solution
Correct answer: C. An ellipse, with the Sun at one focus
1. Kepler's first law states that the orbit of each planet about the Sun is an ellipse.
2. Within that ellipse, the Sun sits at one focus rather than at the geometric center.
3. A circle is only a special case of an ellipse where the two foci coincide, so stating the orbit as a perfect circle is too restrictive in general.
4. A parabola or a spiral does not describe a closed, repeating planetary orbit at all, so neither matches Kepler's first law.
_Source: OpenStax College Physics (CC BY 4.0), Ch 6 "Uniform Circular Motion and Gravitation", section 6.6 Satellites and Kepler's Laws: An Argument for Simplicity_
Related questions
The Moon stays in orbit around the Earth. Which force provides its centripetal force?Why does a centripetal force change a body's direction but never its speed?A stone is whirled on a string in a horizontal circle. What supplies the centripetal forceUnder what condition does an ellipse become a circle?Kepler's third law relates the squares of the periods to which quantity?What does the line from the Sun to a planet sweep out in equal times?What shape does each planet's orbit about the Sun take, and where does the Sun sit?Besides muscle wasting, what else do astronauts lose in microgravity?