Why is water wet? Many people will answer this question by simply saying, "Because it is." The physical properties of water are fundamental to life and nature on Earth, and are often accepted as simple truths. Water is so common on Earth that its physical characteristics have a large impact on the physics of Earth in general. (Physics is the study of matter and energy, and of interactions between the two.) Water covers almost three quarters of the planet's surface. It is the only natural chemical substance that exists as a liquid, solid (ice), and gas (water vapor) within Earth's normal temperature range. Water is liquid in a range critical for biological life (0–100°C, 32–212°F), and liquid water is present almost everywhere on Earth. Water's ability to absorb heat regulates Earth's climate and weather.

Phase Changes

Matter exists in three states, or phases: solid...