All materials you can see and many you can't are grouped by certain characteristics, aka chemical properties. Examples of these characteristics include density, pressure, temperature, volume, phase, and atomic makeup. In this chapter we'll look at questions relating to all of these, but we'll focus on phase, density, and pressure.
When lakes freeze in the winter, they freeze from the top down. So as the top freezes, the water below is actually protected from the cold by the ice. This is how fish can survive.