By placing in a box with sand to shape the metal. The metal is heated until molten (liquid) a mould is made using silica sand or another property that the molten metal will not adherer to. The molds...
mass is sort of like the measure of an objects volume, and has no set number per substance, but density is a fixed figure. As to which object is denser, it depends what type of metal you are talking...
Yes. And if massive enough then the density may increase due to gravitational attraction in a matter of time we can perceive. even with a small mass this is happening, however it may take 1000s to...