Mass is a property of an object. It doesn't change, no matter where the object is.
Weight is the gravitational force between two objects. It depends on the masses of both objects, and also on the distance between their centers, so it changes, depending on the mass of the OTHER object involved, and on the distance between them.
Mass is the amount of matter in an object and stays the same regardless of location, while weight is the gravitational force acting on that mass and can change based on the strength of gravity. For instance, an object's weight on the Moon is significantly less than its weight on Earth due to the difference in gravitational pull. Thus, they are related but distinctly different properties.
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