What causes condensation?

Condensation is caused by a thermodynamic phase change where a gas or vapor loses thermal energy and transforms into a liquid state. This phenomenon is primarily driven by changes in temperature and pressure within an environment containing water vapor or other gases. When warm, moisture-laden air comes into contact with a significantly colder surface, such as a windowpane, a cold beverage glass, or an air conditioning evaporator coil, heat is rapidly transferred from the warm air to the cold object. As the air's temperature drops, its capacity to hold water vapor decreases sharply, causing the relative humidity to reach the saturation point, scientifically known as the dew point. Once this threshold is crossed, the invisible water vapor molecules lose sufficient kinetic energy to remain in a gaseous state, forcing them to bond together and liquefy into visible droplets of water. Similarly, an increase in ambient pressure can also force gas molecules closer together, triggering condensation even without a significant temperature drop. This fundamental physical process occurs constantly in nature, forming morning dew, fog, and clouds, and it is a core mechanism behind refrigeration, distillation, and HVAC operations.