The conservation of $p$ (momentum) is most closely related to which fundamental principle in physics?

• A. The conservation of $E$ (energy)
• B. Newton's third law of motion
• C. Coulomb's law
• D. The law of universal gravitation

Answer: (B)

Verified step by step guidance

1. Understand that the conservation of momentum is a principle stating that the total momentum of a closed system remains constant if no external forces act on it.
2. Recall Newton's third law of motion, which states that for every action, there is an equal and opposite reaction. This implies forces between interacting bodies are equal in magnitude and opposite in direction.
3. Recognize that Newton's third law ensures that when two objects interact, the momentum lost by one object is gained by the other, leading to the overall conservation of momentum in the system.
4. Contrast this with other laws mentioned: Coulomb's law describes electrostatic forces between charges, and the law of universal gravitation describes gravitational attraction, but neither directly guarantees momentum conservation.
5. Conclude that the conservation of momentum is most closely related to Newton's third law of motion because it underpins the mutual forces that ensure momentum is transferred but conserved within a system.