This paper examines the difference between mass and weight, which is discussed very early in most physics courses. Those who indulge in mathematical problems involving weights should know the difference. Mass is often defined as the amount of matter in an object. This usually means the sum of the masses of all the atoms that constitute that particular object, but we would then have to define the mass of an atom. We shall not delve too deeply into this, but should note that the mass of an object remains the same no matter where it is in the universe. Weight, on the other hand, is the force exerted when a mass is acted on by the gravitational attraction of its environment. For objects near the earth's surface, the major gravitational pull is due to the earth, although the sun, moon and planets have a small effect (the moon affects the tides, for example).