anuami wrote:Would an object weigh the same in water as on land?
There is an inherit problem with the question. "Would an object totally submerged in water weigh the same as it does in air?" is a question that eliminates some of the problems. The condition: "in water" could be floating or submerged or partially submerged. The condition: "on land" could be completely burried in dirt, resting on dirt, partially submerged in dirt.
By commonly accepted physics definitions, the "mass" of an object will stay the same as long as it stays intact and nothing is added to the object, so the weight (gravitational force acting on a mass) will be the same as long as you are on or near enough to the same planet. If your project is actually trying to verify these commonly accepted physics definitions, then the problem is beyond this grade level as it will involve coming up with extremely accurate measuring devices in an attempt to find differences that nobody else has found.
The area of interest is more likely to be gravitational force less boyancy force and with those kinds of investigation, the density and other properties of the object (shape, absorbency, etc) will affect the result.