                        Astronomy Picture of the Day

    Discover the cosmos! Each day a different image or photograph of our
      fascinating universe is featured, along with a brief explanation
                    written by a professional astronomer.

                               2021 August 25

                           Solar System Ball Drop
   Video Credit & Copyright: James O'Donoghue (JAXA) & Rami Mandow (Space
                     Australia); Text: James O'Donoghue

   Explanation: Does a ball drop faster on Earth, Jupiter, or Uranus? The
   featured animation shows a ball dropping from one kilometer high toward
   the surfaces of famous solar system bodies, assuming no air resistance.
   The force of gravity depends on the mass of the attracting object, with
   higher masses pulling down with greater forces. But gravitational force
   also depends on distance from the center of gravity, with shorter
   distances causing the ball to drop faster. Combining both mass and
   distance, it might be surprising to see that Uranus pulls the ball down
   slightly slower than Earth, despite containing over 14 times more mass.
   This happens because Uranus has a much lower density, which puts its
   cloud tops further away from its center of mass. Although the falling
   ball always speeds up, if you were on the ball you would not feel this
   acceleration because you would be in free-fall. Of the three planets
   mentioned, the video demonstrates a ball drops even faster on Jupiter
   than either Earth and Uranus.

                       Tomorrow's picture: open space
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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Phillip Newman Specific rights apply.
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                             & Michigan Tech. U.


