The eight planets of the solar system travel in nearly circular orbits around the Sun at different distances and speeds. The inner planets have smaller orbits and travel at faster speeds. The outer planets have larger orbits and travel at slower speeds. Orbits result from a combination of gravity and motion.
Gravity is an attractive force between any objects with mass. The force of gravity between a planet and the Sun, which is by far the most massive object in the solar system, pulls the planet toward the Sun. But because of the way the solar system formed, the planet is also trying to move perpendicular to the gravitational pull of the Sun. As a result, instead of falling into the Sun, the planet travels in an orbit around the Sun. This is the same reason that moons orbit around planets.
The shape of an orbit is actually an ellipse—a shape similar to an oval. The “eccentricity” of an ellipse describes its form, which can be long and thin or very round. The orbital eccentricities of the planets are very small and their orbits look like circles. Other objects, such as comets, have orbits with high eccentricities and travel paths around the Sun that look like stretched out ovals.
Video: Why Doesn't the Moon Fall Down
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Watch this video about how the balance of gravity and motion creates orbits.
Then think about this question: Why don't planets crash into the Sun from the pull of gravity?
Write your anwer in the notes box below.