Observed from an internal reference frame, the net force on a particle is proportional to the time rate of change of its linear momentum. This is Newton's ______ of motion.

Observed from an internal reference frame, the net force on a particle is proportional to the time rate of change of its linear momentum. This is Newton's ______ of motion.

• A. Zeroth Law
• B. First Law
• C. Second Law
• D. Third Law

Answer: (C)

The statement embodies Newton's second law: the net external force on a particle is proportional to the time rate of change of its linear momentum. Since momentum is p = m v, the rate of change is dp/dt. If the mass stays constant, dp/dt = m dv/dt, so the net force equals m times the acceleration. This law directly links what you measure as a force to how the motion changes over time: a force causes velocity (and thus momentum) to change, while no net force leaves momentum constant and the motion in that frame remains uniform. The other laws describe different ideas—thermal equilibrium (zeroth), motion without acceleration in the absence of forces (first), and action–reaction pairs (third)—but the given relationship between force and the rate of momentum change is the essence of the second law.

The statement embodies Newton's second law: the net external force on a particle is proportional to the time rate of change of its linear momentum. Since momentum is p = m v, the rate of change is dp/dt. If the mass stays constant, dp/dt = m dv/dt, so the net force equals m times the acceleration. This law directly links what you measure as a force to how the motion changes over time: a force causes velocity (and thus momentum) to change, while no net force leaves momentum constant and the motion in that frame remains uniform. The other laws describe different ideas—thermal equilibrium (zeroth), motion without acceleration in the absence of forces (first), and action–reaction pairs (third)—but the given relationship between force and the rate of momentum change is the essence of the second law.