The force exerted by a gravitational field on a body, such as the gravity of Earth, is called the weight of the body. The weight of a body is equal to the product of its mass m and the acceleration due to gravity g, (w = mg). Weight should not be confused with mass.

Newton's second law states that the net force F acting on an object is equal to the mass of the object m multiplied by its acceleration a (F = ma). Freely falling bodies experience an acceleration (g) due to the gravitational field of Earth. This force of this field is directed towards the center of Earth. By applying Newton's second law to freely falling bodies, with a = g and F = w, the weight of the body is given as w = mg. Because weight depends upon the gravitational field it varies with geographical location. Because g decreases...