How is mass defined in physics?

Mass in physics is defined as the amount of matter in an object. It is a fundamental property that quantifies how much substance is present in an object, regardless of its state or conditions. Mass is measured in kilograms (kg) and is independent of the object's location or the gravitational field it is in. This intrinsic property is critical because it directly relates to the inertia of an object — the tendency of an object to resist changes in its motion.

Understanding mass as the quantity of matter helps distinguish it from related concepts such as weight, which is the force exerted on an object due to gravity and varies with gravitational strength. This definition is essential in various applications, including mechanics and dynamics, where mass plays a critical role in Newton's laws of motion and in calculating various physical properties like momentum and kinetic energy.