質量と重量

Mass is the amount of matter in an object and remains constant regardless of location. Weight is the force exerted on that mass by gravity and varies depending on gravitational strength. On Earth, weight equals mass multiplied by gravitational acceleration (9.8 m/s²). Understanding this distinction is fundamental to mechanics and physics.

Gravity pulls on an object's mass to create weight. The stronger the gravitational field, the greater the weight for the same mass. On the Moon, where gravity is weaker than Earth, an object weighs less despite having identical mass. This demonstrates that weight depends directly on local gravitational conditions.

Mass is an intrinsic property of matter—the quantity of atoms and molecules composing an object—and does not change with location. Weight, however, is a force that depends on the gravitational field strength at that location. An astronaut's mass stays the same on Earth and in space, but their weight varies significantly.

Mass is measured in kilograms (kg) or grams (g) in the metric system. Weight, being a force, is measured in newtons (N). In some contexts, weight is expressed in pounds-force (lbf) in imperial units. Proper unit selection is essential for accurate calculations in engineering and physics.

Weight is calculated using the formula W = mg, where W is weight in newtons, m is mass in kilograms, and g is gravitational acceleration (approximately 9.8 m/s² on Earth). This equation shows the direct proportional relationship between mass and weight in a given gravitational field.

Yes, an object in a gravity-free environment, such as deep space far from celestial bodies, has mass but effectively zero weight. Mass is an inherent property of matter, while weight requires a gravitational field to exist. This scenario illustrates that mass and weight are fundamentally different physical quantities.