A satellite revolving around the earth is kept on its orbit by?

Analysis

The question asks for the physical force responsible for maintaining a satellite's orbital motion around the Earth. To answer this, we must distinguish between the forces acting on the satellite and the nature of circular motion.

Concept Explanation

1. Circular Motion: For any object to move in a circular path, there must be a net force directed toward the center of the circle. This is called centripetal force.
2. The Role of Gravity: In the case of a satellite, the gravitational pull of the Earth acts as the centripetal force. Without this gravitational pull, the satellite would move in a straight line into space (Newton’s First Law of Motion).
3. Centrifugal Force: This is a "pseudo" or fictitious force that appears to act on an object in a rotating frame of reference. It is not a real force acting on the satellite; rather, it is an effect of the satellite's inertia. Therefore, it is not what "keeps" the satellite in orbit.
4. Frictional Forces: Space is a vacuum, so there is no air resistance or friction to consider in this context.

Step-by-Step Solution

• Step 1: Identify the requirement for circular motion. A satellite in orbit is essentially performing uniform circular motion.
• Step 2: Identify the force providing the inward pull. The Earth's gravitational field provides a constant radial force directed toward the center of the Earth.
• Step 3: Apply the definition of centripetal force. Since the gravitational force is directed toward the center of the orbit, it satisfies the definition of a centripetal force.
• Step 4: Evaluate the options. Since only the centripetal force (provided by gravity) is responsible for the orbital motion, and centrifugal force is not a real force acting on the satellite, Option A is the only physically correct description.

Conclusion

The satellite is kept in its orbit solely by the gravitational force, which acts as the centripetal force.

Exam Tip: Always remember that "Centrifugal force" is a common distractor in physics exams. In reality, it is just the inertia of the body trying to move in a straight line. When asked what keeps an object in a circular path, the answer is always centripetal force.