In engineering and physics, mass is a fundamental property of matter that quantifies the amount of substance in an object. Unlike weight, which depends on gravitational force, mass is an intrinsic property and remains constant regardless of location. It directly influences an object’s resistance to acceleration when a force is applied, as described by Newton’s Second Law (F=ma). Inertia, the tendency of an object to resist changes in motion, is directly proportional to mass, making it a key factor in mechanical design, material selection, and dynamic system analysis. Understanding mass is essential for calculating forces, loads, and energy in engineering applications.

Mass Units
The unit of mass depends on the measurement system used. In the International System of Units (SI), the standard unit of mass is the kilogram (kg), which serves as the base unit for all other mass-related measurements. For smaller masses, the gram (g) is often used, where 1 kg = 1000 g. In large-scale applications, such as in engineering and industry, metric tons (t) are used, with 1 metric ton = 1000 kg.
In the U.S. Customary System, mass is often measured in slugs (slug) or pounds-mass (lbm). The slug is the unit that aligns with Newton’s Second Law, where 1 slug is the mass that experiences an acceleration of 1 ft/s² when subjected to a force of 1 pound-force (lbf). Pounds-mass (lbm) are are sometimes used, though they require conversion when working with force and acceleration, since standard gravitational acceleration (g=32.174 ft/s2) must be accounted for.