If the attraction of the sun is suddenly ceased, the earth would continue to move in a straight line making a…

Analysis of the Question

The question asks us to identify the specific law of motion that explains why an object (the Earth) would continue moving in a straight line if the external force (the Sun's gravitational pull) acting upon it were suddenly removed.

Concept Explanation

To solve this, we must look at Newton’s Laws of Motion:

1. Newton’s First Law (Law of Inertia): This law states that an object will remain at rest or continue to move at a constant velocity in a straight line unless acted upon by an external force. Inertia is the property of matter that resists a change in its state of motion.
2. Newton’s Second Law: This law relates force, mass, and acceleration ($F = ma$). It explains what happens when an external force is applied.
3. Newton’s Third Law: This law states that for every action, there is an equal and opposite reaction.

In the Earth's orbit, the Sun's gravitational force acts as a centripetal force, constantly pulling the Earth toward the center and forcing it to move in a circular path. If that force ceases, there is no longer a net force to pull the Earth out of its straight-line path. According to the First Law, the Earth will simply continue moving in the direction it was headed at the exact moment the force vanished—which is along the tangent to its orbit.

Step-by-Step Solution

1. Identify the state of motion: The Earth is currently in a state of uniform circular motion due to the Sun's gravity.
2. Identify the change: The "attraction of the sun" (the external force) is removed.
3. Apply the law: According to Newton's First Law, an object in motion stays in motion in a straight line unless an external force changes that state. Without the gravitational force, there is no longer a "change" in direction (acceleration).
4. Conclusion: The Earth will follow the path of its instantaneous velocity, which is a straight line tangent to the orbit. This is a classic demonstration of the Law of Inertia.

Correct Answer

The statement is derived from Newton's First Law of Motion.

Exam Tip

Whenever you see a question about an object "continuing its state" or "moving in a straight line" when forces are removed or balanced, immediately think of Newton's First Law (Inertia). It is the law that defines the natural tendency of objects to keep doing exactly what they are already doing!