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The Orbit of the Planets (continued).
If the forces acting on the Earth were balanced,
then the Earth would move through
space in a straight line
at a constant velocity (see forces and motion).
The Earth is trying to move past the Sun.
The Sun's gravity is pulling the Earth
sideways.
There are no
other forces acting on the
Earth,
no friction because the Earth is moving
through empty space.
The Earth moves in a direction between the
two arrows.
The attraction of gravity between
the two masses
(the Sun and the Earth)
stays the same
as long as the distance between them
stays the same.
The Earth must move in a circle
to
remain the same distance from the Sun.
The force that keeps an object moving in a
circle
is called the centripetal force (continued on the next page).
Links
Planets
The Solar System
Revision Questions
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