3. Changes of State & the Energy Behind Them

The water cycle works because water easily changes between three states — solid (ice), liquid (water), and gas (water vapor) — at the everyday temperatures found on Earth. Each change involves energy.

• Evaporation (liquid → gas) absorbs energy. That's why evaporating sweat cools your skin — it carries heat away.
• Condensation (gas → liquid) releases that stored energy back into the air. This released heat is a major fuel for clouds and storms.
• Melting (solid → liquid) absorbs energy; freezing (liquid → solid) releases it.

The Sun is the energy source that lifts water into the air; gravity later brings it back. And note: water vapor is an invisible gas. The white 'steam' you see above a kettle or as clouds is not vapor — it is vapor that has already condensed into tiny visible droplets.

⚠️ Common misconception: clouds and 'steam' are not water vapor. Water vapor is invisible; what you see are tiny liquid droplets (or ice crystals) that formed when vapor condensed.

💡 Tip: add energy → toward gas; remove energy → toward solid. Evaporation cools (absorbs heat); condensation warms the air (releases heat).