Which one among the following statements is not correct?

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UPSC CDS-I 2025 (General Studies) Official Paper (Held On: 13 Apr, 2025)
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  1. All bodies in the universe attract each other due to the gravitational force.
  2. Newton's law of gravitation follows from Newton's laws of motion.
  3. The value of g (acceleration due to gravity) at the centre of the Earth is zero.
  4. Mass and weight are measured in different units.

Answer (Detailed Solution Below)

Option 2 : Newton's law of gravitation follows from Newton's laws of motion.
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The correct answer is Newton's law of gravitation follows from Newton's laws of motion..

Key Points

  • Newton's law of gravitation is a standalone law that describes the attractive force between two masses and is not derived from Newton's laws of motion.
  • Newton's laws of motion describe the relationship between the forces acting on a body and its motion, but they do not explain why bodies exert gravitational attraction.
  • Newton's law of gravitation was formulated based on observational data and is independent of the three laws of motion.
  • The gravitational force between two bodies is proportional to the product of their masses and inversely proportional to the square of the distance between them.
  • Newton's laws of motion and the law of gravitation are foundational but distinct components of classical mechanics.

Additional Information

  • Newton's Law of Gravitation:
    • States that every particle in the universe attracts every other particle with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.
    • Mathematically: F = G (m₁m₂)/r², where G is the gravitational constant.
  • Newton's Laws of Motion:
    • First Law: A body remains at rest or in uniform motion unless acted upon by an external force (Law of Inertia).
    • Second Law: The rate of change of momentum of a body is directly proportional to the applied force (F = ma).
    • Third Law: For every action, there is an equal and opposite reaction.
  • Gravitational Constant (G):
    • A fundamental constant of nature with a value of approximately 6.674 × 10⁻¹¹ N(m²/kg²).
    • It quantifies the strength of the gravitational force in Newton's law of gravitation.
  • Gravitational Force vs. Weight:
    • Gravitational force is the mutual force of attraction between two masses.
    • Weight is the gravitational force exerted by the Earth on a body near its surface (Weight = mass × g).
  • Gravitational Force at Earth's Center:
    • At the center of the Earth, the gravitational force due to the Earth's mass cancels out, resulting in zero acceleration due to gravity (g = 0).
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