Mass is a fundamental property of [[Matter|matter]] that measures the amount of [[Substance|substance]] in an object. It is independent of [[Gravity|gravity]], meaning an object's mass remains the same whether it's on Earth, the Moon, or in space. Mass is measured in **kilograms (kg)** in the [[SI System|SI system]]. Mass also determines an object's resistance to changes in motion ([[Inertia|inertia]]) and contributes to [[Newton's Law of Universal Gravitation|gravitational attraction]] between objects.