Mass and Weight

Mass and Weight

In common usage, the terms mass and weight are interchangeable. However, in physics and engineering, mass and weight refer to two different quantities and should not be confused.

Mass is a physical property of a body and is a measure of its “resistance to acceleration” (inertia) when a force is applied. Although not often relevant to FEA, the mass of an object determines how great its gravitational attraction to other bodies is. The SI unit for mass is kilogram, or kg.

Weight, on the other hand, is related to the force acting on an object, either due to gravity, or a reaction force which is holding it in place. The unit for weight is the same as that for force, which is newton, or N.

As weight is dependent on gravity, whereas mass is not, an object will have a different weight on the moon and on earth, as they have different gravitational strengths, but the same mass everywhere. On Earth, 1kg is equal to approximately 9.81N.

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