Why is mass constant but weight is not?

Mass is constant because it is the amount of matter in an object, while weight changes due to variations in gravitational force.

Mass is a fundamental property of an object, representing the amount of matter it contains. It is measured in kilograms (kg) and remains constant regardless of where the object is located. Whether you're on Earth, on the Moon, or in the vacuum of space, your mass remains the same because the amount of matter in your body doesn't change.

Weight, on the other hand, is a force that is the result of gravity acting on mass. It is measured in newtons (N) and can change depending on the strength of the gravitational field where the object is located. For example, if you were to stand on the Moon, your weight would be less than it is on Earth because the Moon's gravitational field is weaker. However, your mass would remain the same because the amount of matter in your body hasn't changed.

This distinction between mass and weight is crucial in physics. Mass is a scalar quantity, meaning it only has magnitude and no direction. Weight, however, is a vector quantity, meaning it has both magnitude (the actual weight) and direction (towards the centre of the gravitational field).

In summary, mass is an intrinsic property of an object and remains constant regardless of location, while weight is a force that depends on the local gravitational field and can therefore change. Understanding this difference is fundamental to the study of physics.