|MadSci Network: Physics|
Hi James, Whether or not something floats depends not just on its mass, but its density (which is its mass/volume). If it will displace less mass than an equivalent volume of water, then that object will float. Ice floats on water because it has a lower density. Marbles will sink because they are denser than water. It is possible to have a very dense material float if there is enough empty volume to make the average density less than that of water, such as a hollow marble. You could also , for example, make it bowl shaped or make it with a large bottom surface area and shallow sides (much like a cookie sheet). In all these cases you have the dense material filled with air which lowers the average density. Hence, it is possible to float something that weighs more than the water you are floating it in. In principle you could float a 1000000 pound boat in 100 pounds of water by making the boat out of a material that has a very low density or by making it with a very large, thin bottom. However, it is not really very practical as it would be difficult to find a 1000000 pound boat that will fit in the space taken up by 100 pounds of water. Erika
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