Mass and weight. Two samples of material placed on scales show different masses and weights. The mass of an object is determined by the quantity of matter of which it is composed, and does not vary according to forces acting upon it. The weight of on object is the force experienced by that object due to gravity. In this case, the two samples have different weights (measured in Newtons) because they have different masses (measured in grams or kilograms) upon which gravity is acting. They are composed of different numbers of atoms, which constitute matter.