Which statement aligns with Newton's First Law of Motion as described?

• A. For every action, there is an equal and opposite reaction
• B. Unbalanced forces cause changes in motion
• C. An object in motion requires a continuous force to keep moving
• D. Force equals mass times acceleration

Answer: (B)

Newton's First Law centers on inertia: an object keeps doing what it's doing (staying at rest or moving with constant velocity) unless a net external force makes it change. The idea is that motion only changes when forces are unbalanced. The statement about unbalanced forces causing changes in motion captures that connection between net force and a change in velocity, which aligns with the First Law's core idea.

The other options point to different ideas: action and reaction is Newton's Third Law, not the First; saying a continuous force is required to keep moving contradicts inertia; and the equation F = ma is the Second Law, describing how a net force produces acceleration. So, among the choices, describing how unbalanced forces lead to a change in motion best exemplifies the principle described by Newton's First Law.