The difference between mass and weight lies in their definitions and physical meanings:

• Mass is the amount of matter contained in an object. It is a scalar quantity and does not change regardless of location. Mass measures an object's resistance to changes in motion (inertia) and is measured in kilograms (kg) or pounds (lb) as a measure of matter

• Weight is the force exerted on that mass by gravity. It is a vector quantity (has direction) and depends on both the mass of the object and the gravitational acceleration at its location. Weight is measured in newtons (N), which are units of force. Because gravity varies by location (Earth, Moon, other planets), weight changes accordingly, while mass remains constant

The relationship between them is given by the formula:

Weight(W)=Mass(m)×Acceleration due to gravity(g)\text{Weight}(W)=\text{Mass}(m)\times \text{Acceleration due to gravity}(g)Weight(W)=Mass(m)×Acceleration due to gravity(g)

For example, a person with a mass of 70 kg weighs about 686 newtons on Earth (where g≈9.8 m/s2g\approx 9.8,m/s^2g≈9.8m/s2), but would weigh only about 112 newtons on the Moon due to weaker gravity, though their mass stays the same

. In everyday language, mass and weight are often used interchangeably, but scientifically they are distinct: mass is a measure of matter, weight is a measure of gravitational force on that matter

. Summary:

Aspect| Mass| Weight
---|---|---
Definition| Amount of matter in an object| Gravitational force on the object
Quantity type| Scalar| Vector
Units| Kilograms (kg), pounds (lb)| Newtons (N)
Depends on| Amount of matter only| Mass and local gravity
Changes with location?| No| Yes
Measures| Inertia (resistance to motion)| Force due to gravity

This distinction is crucial in physics and engineering to avoid confusion between how much matter an object has and how heavy it feels due to gravity.