Earth stays in orbit primarily due to the Sun's gravity. Here’s how it works:
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Gravitational Pull: The Sun, being a massive object, exerts a strong gravitational force on Earth. This gravitational attraction pulls Earth toward the Sun.
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Inertia: At the same time, Earth has a certain amount of inertia due to its motion. Inertia is the tendency of an object to maintain its current state of motion (in this case, moving in a straight line).
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Balance of Forces: The combination of the Sun's gravitational pull and Earth's inertia leads to a stable orbit. While the Sun's gravity pulls Earth inward, Earth's inertia keeps it moving forward. This balance results in an elliptical orbit around the Sun.
If we consider the other options:
- Earth’s gravity helps keep objects on its surface but does not directly affect Earth's orbit around the Sun.
- The moon’s inertia isn't relevant in this context; while the Moon affects Earth’s gravitational field and has its own orbit around Earth, it does not play a significant role in Earth's orbit around the Sun.
- The Sun's inertia isn’t a concept that applies in this context, as objects do not orbit due to their inertia alone.
In summary, the Sun's gravity is the force that primarily keeps Earth in its orbit.