Which statement is a concise expression of Newton's Second Law?

• A. Force = mass x acceleration
• B. Acceleration equals force divided by mass
• C. Energy equals mass times velocity
• D. For every action there is an equal and opposite reaction

Answer: (A)

Newton's Second Law states that the net external force acting on an object produces acceleration in that object, with mass determining how much the motion changes. In its most practical form for constant mass, this relationship is written as F = m a, which directly ties force to the resulting acceleration and uses mass as the factor that resists changes in motion. This concise expression is preferred because it clearly shows force as the cause and acceleration as the effect, with mass quantifying the response.

The statement that acceleration equals force divided by mass is mathematically equivalent when mass is constant, but F = m a is the standard, direct way to express the law. The other two options refer to different ideas: one describes kinetic energy (which is actually (1/2) m v^2, not m v), and the other is Newton's Third Law about action and reaction, not the force–motion relationship.