GEF

Unit 2  |  Water Science and the Water Cycle 45 The density (mass per unit volume) of water changes between the different states. In most substances, decreasing tempera- ture increases density, meaning the substance contracts and its volume decreases as it cools. As water gets colder it follows this pattern, up to a point. When water freezes, the pattern reverses—density decreases and volume increases. One result of this phenomenon is that ice floats, as observed when dropping an ice cube into a glass of water. This property has important implications for life on Earth. For example, water in a pond or lake freezes from the top down, allowing aquatic organisms to live through the winter. Lights travels through water to coral habitats, providing means for abundant marine life to thrive. The amount of heat energy a liquid can store before its tem- perature begins to change is called its specific heat capacity . Water has a high specific heat capacity, enabling it to store a DENSITY A measure of mass per unit of volume. SPECIFIC HEAT CAPACITY The amount of heat that is required to change the tem- perature of a substance by a given amount.