Its direction of motion changes continuously.
Explanation
The motion of the Moon around the Earth is an example of Uniform Circular Motion (approximated). In physics, velocity is a vector quantity, meaning it possesses both magnitude (speed) and direction. Acceleration is defined as the rate of change of velocity. Therefore, any change in either speed or direction results in acceleration.
Detailed Analysis
- Its orbital speed increases continuously. is Incorrect: In an idealized circular orbit, the orbital speed (magnitude of velocity) remains constant. While the Moon's orbit is slightly elliptical causing minor speed variations, the fundamental reason the motion is classified as "accelerated" is the continuous change in direction, not the change in speed.
- Its direction of motion changes continuously. is Correct: As the Moon orbits the Earth, its direction of motion changes at every point along the trajectory. Since velocity includes direction, a change in direction implies a change in velocity. By definition, a change in velocity constitutes acceleration. This specific acceleration is directed towards the center of the Earth and is known as centripetal acceleration.
- It covers unequal distances in equal time intervals. is Incorrect: This statement contradicts the nature of uniform circular motion, where an object covers equal distances in equal intervals of time. While the Moon's actual orbit follows Kepler's laws (equal areas in equal time), this option does not explain the fundamental definition of accelerated motion in this context.
- It moves in a linear trajectory. is Incorrect: The trajectory of the Moon is curvilinear (elliptical/circular), not linear. A linear trajectory with constant speed would not be accelerated motion.
Key Takeaway: In circular motion, even if the speed is constant, the body is always accelerating because the direction of velocity changes continuously.