##### Mass, Weight, Density

Weight. The weight of an object is defined as the force of gravity on the object and may be calculated as the mass times the acceleration of gravity, w = mg.Since the weight is a force, its SI unit is the newton.. For an object in free fall, so that gravity is the only force acting on it, then the expression for weight follows from Newton's second law.. You might well ask, as many do, "Why do ...