What force keeps planet earth in its orbit?

• A. The sun's gravity
• B. Earth's gravity
• C. Magnetic forces
• D. Nuclear forces

Answer: (A)

Orbital motion is governed by gravity from the body being orbited. The Earth stays in orbit because the Sun’s gravity pulls on it, providing the centripetal force that keeps its path curved rather than straight. Earth moves forward through space with enough velocity that the Sun’s gravitational pull continually bends this motion into an orbit, rather than letting Earth fall directly toward the Sun. Because the Sun is vastly more massive than Earth, its gravity dominates the interaction and sets the orbital dynamics.

Earth’s own gravity primarily affects objects near its surface and does not signficantly influence the solar orbit. Magnetic forces are negligible at planetary distances, and nuclear forces operate at subatomic scales, not across solar-system distances. So the Sun’s gravity is the force that keeps Earth in its orbit.