Newton's second law is commonly written as which formula?

• A. F = m a
• B. E = m c^2
• C. P = m v
• D. W = F d

Answer: (A)

When a net force acts on an object, it changes the object's motion in a way that depends on its mass. Newton's second law states that the net force equals the mass times the acceleration, with the acceleration in the same direction as the net force. The mass acts as the proportionality constant: for a given force, a larger mass means smaller acceleration, and for a given mass, doubling the force doubles the acceleration. This relationship also provides a practical way to use the formula: a = F/m, so you can find the acceleration if you know the force and mass, or find the needed force if you know the mass and desired acceleration. The units line up cleanly too—newton (N) is kg·m/s², which matches F = ma. The other expressions describe different ideas: energy-mass equivalence, momentum, and work, respectively.