Well... for common application, yes. Just don't tell that to any physicists.

The short answer is that there is often no difference. A common meaning of "weight" is "mass." The original meaning of "weight," still in general use today, is equivalent to mass. But a definition common in physics uses "weight" for a particular kind of force * To understand the differences we need to compare a few points: 1) Mass is a measurement of the amount of matter something contains, while Weight is the measurement of the pull of gravity on an object. 2) Mass is measured by using a balance comparing a known amount of matter to an unknown amount of matter. Weight is measured on a scale. 3) The Mass of an object doesn't change when an object's location changes. Weight, on the other hand does change with location. Sorry about the misunderstanding Farino, youre right, I did mix in the density mistakenly. http://www.nyu.edu/pages/mathmol/textbook/weightvmass.html Basically, on Earth, yes, Mass and Weight can be interchangeable in most cases, I hope this is a bit more helpful.

Mass is a measure of how much matter an object has. The weight of an object depends on where it is, while its mass stays the same. So on earth they are reasonably equivalent, but strictly speaking they are not the same.

"The distinction between mass and weight is unimportant for many practical purposes because the strength of gravity is very similar everywhere on the surface of the Earth. In such a constant gravitational field, the gravitational force exerted on an object (its weight) is directly proportional to its mass. So, if object A weighs, say, 10 times as much as object B, then object A's mass is 10 times that of object B. This means that an object's mass can be measured indirectly by its weight (for conversion formulas see below). For example, when we buy a bag of sugar we can measure its weight (how hard it presses down on the scales) and be sure that this will give a good indication of the quantity that we are actually interested in, which is the mass of sugar in the bag. Nevertheless, the Earth's gravitational field can vary by as much as 0.5% at different locations on Earth (see Earth's gravity). These variations alter the relationship between weight and mass, and must be taken into account in high precision weight measurements that are intended to indirectly measure mass. To eliminate this variation, when the weight of objects is used in commerce, the value given is what they would weigh at a nominal standard gravitational acceleration of 9.80665 m/s2 (approx. 32.174 ft/s2) Spring scales, which measure local weight, must be calibrated at the location at which they will be used to show this standard weight, to be legal for commerce." "The difference between mass and force may be important when [...] an object is submersed in a fluid (for instance, a brick weighs less when placed in water, and helium balloon in the atmosphere appears to have negative weight)." Source and further information: http://en.wikipedia.org/wiki/Weight Further information: http://www.answerbag.com/a_view/2429890