Mass Defined as Inertia

Steps:

• Recall that mass is a fundamental property in physics, distinct from weight.
• Identify inertia as the resistance to changes in motion, per Newton's first law.
• Match this to option A, which describes resistance to motion change.
• Eliminate other options by distinguishing mass from gravity-dependent concepts.

Why A is correct:

• Mass is inertia, the property that resists acceleration, as in F = ma where mass m determines force needed for motion change.

Why the others are wrong:

• B describes weight, the gravitational force on mass.
• C refers to composition, not a measure of mass.
• D equates mass to weight, which varies by location unlike invariant mass.

Final answer: A