Difference between Mass and weight

Mass and weight are related but distinct concepts in physics

Mass

• Mass is a measure of the amount of matter in an object. It is a scalar quantity and is constant, meaning it does not change regardless of an object's location in the universe.
• The SI unit of mass is the kilogram (kg).

Weight

• Weight is the force exerted on an object due to gravity. It is a vector quantity and depends on both the mass of the object and the gravitational field strength where the object is located.
• The SI unit of weight is the newton (N).

Now, let's illustrate the difference between mass and weight using the examples of an object on Earth and on the Moon:

Example: Object on Earth

• Suppose you have a mass of 70 kilograms (kg) on Earth.
• On Earth, the acceleration due to gravity is approximately 9.81 meters per second squared (m/s²).
• To find your weight on Earth, you use the formula: Weight (W) = Mass (m) × Acceleration due to gravity (g)
• Weight (W) = 70 kg × 9.81 m/s² ≈ 686.7 N
• So, your weight on Earth is approximately 686.7 newtons.

Example: Object on the Moon

• Now, let's consider the same object with a mass of 70 kg on the Moon.
• The Moon has a weaker gravitational field than Earth, with an acceleration due to gravity of approximately 1.625 m/s².
• To find your weight on the Moon, you use the same formula: Weight (W) = Mass (m) × Acceleration due to gravity (g)
• Weight (W) = 70 kg × 1.625 m/s² ≈ 113.75 N
• So, your weight on the Moon is approximately 113.75 newtons.

In these examples, your mass remains the same (70 kg) whether you are on Earth or the Moon because mass is an intrinsic property of an object. However, your weight changes because it depends on the gravitational field strength of the celestial body you are on. On Earth, with a stronger gravitational field, you have a greater weight, while on the Moon, with a weaker gravitational field, you have a lower weight. This illustrates the fundamental difference between mass and weight.