Weight and mass are related but distinct physical properties. Here's a clear breakdown of their differences:
- Mass:
- Definition: Mass is the amount of matter in an object. It’s a measure of how much "stuff" an object contains.
- Unit: Measured in kilograms (kg) or grams (g) in the SI system.
- Property: Intrinsic and constant; it doesn’t change regardless of location. For example, a 1 kg object has the same mass on Earth, the Moon, or in space.
- Type: Scalar quantity (has magnitude only).
- How Measured: Typically measured using a balance, which compares an object’s mass to a standard mass.
- Weight:
- Definition: Weight is the force exerted by gravity on an object’s mass. It depends on both the mass and the gravitational field strength.
- Unit: Measured in newtons (N) in the SI system, though often expressed in kilograms-force or pounds in everyday use.
- Property: Varies with location due to differences in gravity. For example, an object weighs less on the Moon (1/6th Earth’s gravity) but has the same mass.
- Type: Vector quantity (has magnitude and direction, downward toward the gravitational source).
- How Measured: Measured using a spring scale, which detects the force exerted by gravity on the object.
- Key Relationship:
- Weight (W) = Mass (m) × Gravitational acceleration (g).
- On Earth, g ≈ 9.8 m/s². So, a 1 kg mass weighs 9.8 N on Earth but less on the Moon (g ≈ 1.6 m/s²).
- Example:
- A 10 kg object:
- Mass: Always 10 kg, anywhere.
- Weight on Earth: 10 kg × 9.8 m/s² = 98 N.
- Weight on Moon: 10 kg × 1.6 m/s² ≈ 16 N.
- A 10 kg object:
In summary, mass is about the quantity of matter and stays constant, while weight is the gravitational force on that mass and changes with gravity.
