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Donut Shaped Planet
Name: Unknown
Status: N/A
Age: N/A
Location: N/A
Country: N/A
Date: Around 1993
Question:
What would the gravity be like on a donut shaped planet and could
such a planet exist?
Replies:
That is an interesting question. The problem can be done the
hard way, by integrating the gravitational potential for such a system... but
a rough answer can be obtained just by looking at the way gravity works. If
you were standing on the planet, then each little piece of the planet is
putting a little bit of force on you, attracting you towards it. If you were
standing on the outside, with the center of the donut hole exactly beneath
your feet, then you would feel a strong gravitational force straight down,
because all the parts of the donut are on the same side of you, and the
average direction is straight down. If you were standing on the inside, with
your head pointing to the donut hole center, then you would feel a somewhat
weaker gravitational force keeping your feet on the donut. The near parts of
the donut are exerting the stronger force, and so keeping you attached, but
the other side of the donut is above your head, and is exerting a weak force
in that direction so that the force keeping your feet down is partially
counteracted. If you stand at any other point on the rim, then the force on
you is not quite vertical - the net force does not point through your feet,
but there will be a small amount due to the other side of the donut pulling
you towards it. Such a planet certainly could exist. However, if it were the
size of the earth it would quickly collapse into something like a sphere, due
to the gravitational action of one side of the donut on the other -for a
really big mass (like the earth) the force is so strong that no material would
be strong enough to oppose it.
A. Smith
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Update: June 2012
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