The weight of an object is the force with which it is pulled toward the center of the earth. This force is directly related to the mass of the object, a basic characteristic of matter. It is also dependent on the distance of the object from the center of the earth.
   The pull of the earth, called the force of gravity, is slightly greater at the poles than at the equator because of the fact that the earth is flatter at the poles. The earth's surface is actually nearer its center there. This resulted from the centrifugal force of the earth's rotation. An object that weighs 300 pounds at the poles will weigh 299 pounds at the equator.
   Weight is greatest at the earth's surface. Weight decreases proportionately the farther one is above or below the surface of the earth. At an altitude of two miles, or at four miles below the earth's surface, the weight of an object would be about 0.1 per cent of its weight at the surface.
   Weight is measured in pound-weight or gram-weight. One pound-weight is defined as the weight of one pound mass at a location where the acceleration of gravity is 32.1740 feet per second squared. One gram-weight is the weight of one gram mass in a similar location. Pound- or gram-weights of materials are convenient measures of the quantity of a substance.
   The concept of weightlessness means that there is no resistance to the pull of gravity on an object.