Weight
Explanation
Physical quantities are categorized into scalars and vectors. Scalar quantities are defined solely by magnitude. Vector quantities are defined by both magnitude and direction, and they adhere to the laws of vector addition.
Option Analysis
- Mass is Incorrect: Mass is a scalar quantity. It measures the amount of matter contained in a body and possesses only magnitude, independent of direction.
- Weight is Correct: Weight is a vector quantity. It represents the gravitational force acting on an object, directed towards the center of the Earth (or other celestial bodies). As a force ($W = mg$), it possesses both magnitude and a specific direction.
- Density is Incorrect: Density is a scalar quantity defined as mass per unit volume ($\rho = m/V$). Since it is derived from two scalar quantities (mass and volume), it has no direction.
- Universal Gravitation Constant is Incorrect: The Universal Gravitation Constant ($G$) is a scalar physical constant. It represents the proportionality factor in Newton's Law of Universal Gravitation and does not possess direction.
Key Takeaway: The fundamental distinction between mass and weight is that mass is an intrinsic scalar property of matter, whereas weight is a vector quantity representing the force of gravity acting on that mass.