floating scale 3 in 1

thingiverse

The concept: I wanted to create something that showcases the fundamental principles of buoyancy, displacement, and density for the science challenge. Density is determined by dividing mass by volume, so both must be measured accurately. Volume can be calculated by measuring the water displaced in a container, while mass is measured using the principle of buoyancy. To demonstrate the comparison between two objects with different densities but identical masses as Archimedes did, I aimed to create something that achieves this. The design: To measure volume - A cylinder is filled halfway with water and marked at the level. Coins are then tossed into the cylinder, causing the water to rise. The difference in height corresponds to the volume of the coins divided by the surface area of the water. If the surface area is 1000mm^2, the water will rise 1mm for every cm^3 of coin volume. To calculate this area, we must determine the radius of the cylinder, which is the square root of 1000mm^2/pi = 17.84mm. To measure weight - The cylinder has an outside radius of 25.23mm and an area of 2000mm^2, causing it to sink 1mm for every 2g. This can be measured using the outer part that floats. To compare density - On each side of the scale, an equal amount of weight is placed, but on one side, the material is denser than on the other. The scale is then immersed in water where the less dense material displaces more water and this side of the scale rises. The test: For testing purposes, I used 50c coins weighing 7.8g with a density of 8.54 g/cm^3 and a silver coin weighing an ounce (31.1g) with a density of 10.49 g/cm^3.