Which quantity is described as inertia and is central to Newton's laws, with F = m a and p = m v?

• A. Energy
• B. Momentum
• C. Force
• D. Mass

Answer: (D)

Inertia is the resistance to changes in motion. The quantity that embodies that resistance is mass. With a given push, a larger mass resists acceleration more, which is captured by F = m a: for the same force, acceleration is smaller as mass increases. In momentum p = m v, mass also scales how much momentum an object has at a certain speed. So mass is the intrinsic property that measures inertia, while energy, force, and momentum describe other aspects of motion.