The rate of change of momentum is proportional to the applied unbalanced force.
Explanation
Newton's Laws of Motion constitute the foundation of classical mechanics, describing the relationship between the motion of an object and the forces acting upon it. While the First Law defines inertia and the Third Law describes interaction, the Second Law provides a quantitative measure of force.
Option Analysis
- The rate of change of momentum is proportional to the applied unbalanced force. is Correct: Newton's Second Law of Motion states that the rate of change of momentum of a body is directly proportional to the applied unbalanced force and takes place in the direction of the force. Mathematically, this is expressed as \( F = \frac{dp}{dt} \), which simplifies to \( F = ma \) (Force = mass × acceleration) when mass remains constant.
- The total momentum of an isolated system remains constant. is Incorrect: This statement describes the Law of Conservation of Momentum, which states that in the absence of an external force, the total momentum of an isolated system remains constant.
- Every action has an equal and opposite reaction. is Incorrect: This statement defines Newton's Third Law of Motion, which asserts that for every action, there is always an equal and opposite reaction.
- An object remains in a state of rest unless acted upon by an external force. is Incorrect: This statement defines Newton's First Law of Motion (Law of Inertia), which states that a body continues in its state of rest or uniform motion in a straight line unless compelled by an external force to change that state.
Key Takeaway: Newton's Second Law establishes the mathematical relationship between force, mass, and acceleration, defining force as the rate at which momentum changes over time.