Why is mass a scalar quantity but weight a vector?

Mass is a scalar quantity because it only has magnitude, while weight is a vector because it has both magnitude and direction.

Mass is a fundamental property of an object, representing the amount of matter it contains. It is a scalar quantity, meaning it only has magnitude and no direction. It remains constant regardless of where the object is in the universe. For example, if you have a 1 kg apple, it will remain 1 kg whether it's on Earth, on the Moon, or in deep space. This is because mass is an intrinsic property of the object, not dependent on external factors.

On the other hand, weight is the force exerted on an object due to gravity. It is a vector quantity, meaning it has both magnitude (how strong the force is) and direction (which way the force is pulling). The weight of an object can change depending on where it is in relation to a gravitational field. For instance, the same 1 kg apple would weigh less on the Moon than on Earth because the Moon's gravitational field is weaker. The direction of the weight is always towards the centre of the gravitational field, which is why we say 'weight pulls downwards'.

In summary, mass is a scalar quantity because it only involves the amount of matter in an object and does not depend on its location or direction. Weight, however, is a vector quantity because it is a force that has a specific direction (towards the centre of a gravitational field) and its magnitude can change depending on the strength of the gravitational field.