Mass is a fundamental property that measures the amount of matter in an object. Unlike weight, mass remains constant regardless of where the object is located. Whether on Earth or the Moon, a 5-kilogram object always has the same mass. Mass is measured in kilograms and is a scalar quantity, meaning it has magnitude but no direction.
Gravity is a fundamental force of attraction that exists between all objects with mass. The strength of gravitational force depends on the masses of the objects and the distance between them, following Newton's law of universal gravitation. On Earth, gravity causes objects to accelerate downward at approximately 9.8 meters per second squared. This gravitational acceleration is what we experience as the pull toward Earth's center.
Weight is the force exerted on an object due to gravity. Unlike mass, weight changes depending on the gravitational field strength of the location. Weight equals mass times gravitational acceleration. For example, a 5-kilogram object weighs 49 Newtons on Earth but only 8 Newtons on the Moon, because the Moon's gravity is weaker. Weight is a vector quantity, always pointing toward the center of the gravitational source.
Let's summarize the key differences. Mass is the amount of matter in an object, measured in kilograms, and remains constant everywhere. Weight is the force of gravity acting on that mass, measured in Newtons, and varies with location. Gravity is the fundamental force of attraction between masses. Remember: mass is what you have, weight is what you feel, and gravity is what causes that feeling. A 5-kilogram object always has 5 kilograms of mass, but its weight changes from 49 Newtons on Earth to just 8 Newtons on the Moon due to different gravitational strengths.
Understanding these concepts has practical applications. In space missions, engineers calculate fuel requirements based on mass, not weight, since weight changes throughout the journey. When designing buildings and bridges, engineers must account for weight forces that structures will experience. In scientific research, distinguishing between mass and weight helps us understand inertial versus gravitational effects. A spacecraft with 1000 kilograms of mass weighs 9800 Newtons on Earth but only 1600 Newtons on the Moon, yet its mass remains constant throughout the mission.