What causes the grass to be wet in the morning if the temperature dropped the night before?

Answer 1

Floating water molecules, or water vapor, are always present in the air. The warmer the air is, the more water vapor it can hold. When air cools, it reaches a temperature at which it cannot continue to hold its moisture; this temperature is called the dew point. At this temperature water vapor will condense, becoming a liquid. At night, without the warmth of the Sun, the temperature of the ground and the grass that covers it becomes cooler. If it becomes cooler than the dew point of the air that touches it, condensation will occur. The grass will be covered with droplets of water by morning, even though no rain has fallen during the night. This moisture on the grass is called dew, and it often evaporates in the morning sunlight before we get to see it. (If the temperature at night drops to below freezing, the dew will become frost.) The same thing happens when the glass filled with a cold drink "sweats" on a warm summer day, or when your eyeglasses fog up as you come indoors from the cold.