Below this pressure, water returns to its low-density phase; above it ... effects that directly modify the behavior of the water molecules, just as one person influences the behavior of another.

These low masses help explain why polyethylene has a low density. Another reason is that these long skinny molecules are loosely packed together. Polyvinyl chloride is made up of carbon, hydrogen, and ...

Therefore, differences in density between metals are usually based on the size and mass of the atoms. Wood is made from a long molecule called cellulose. Cellulose is made from glucose molecules ...