Why does styrofome float on water?

Answer 1

Styrofoam is mostly air, trapped in little cells inside plastic. It's like the plastic version if Rice Krispies, which also float on water. Until they get soggy and sink. Air floats because it is less dense than water. Other things, like oil, are also less dense than water and float on it. Some things, like most rocks, are denser than water and sink in it.

If you haven't figured it out yet, whether something floats depends on how dense it is. If you haven't figured that out by now, you are probably pretty dense, too!

Ice is less dense than liquid water, but it is of course made of water, too. When you put ice cubes into your drink, they float. But as they melt, the cold meltwater mixes into the drink around it and makes your whiskey taste more like schnapps.