Final answer:
Humidity is the amount of water vapor in the air, with relative humidity being a percentage measure comparing current water vapor levels to the maximum amount air can hold at a given temperature. Relative humidity reaches 100% at the dew point, preventing further evaporation. Temperature affects the capacity of air to hold moisture, with warmer air able to contain more.
Step-by-step explanation:
The scientific definition of humidity refers to the amount of water vapor present in the air. Specifically, when discussing humidity, we are often referring to relative humidity, which is a measure of the current amount of water vapor in the air compared to the maximum amount the air can hold at that temperature. Relative humidity is expressed as a percentage, with 100% being the point at which the air is at saturation and cannot hold any more water vapor, leading to inhibited evaporation. Temperature plays a significant role in how much water vapor air can contain; warmer air can hold more moisture. As the temperature drops in the evening, relative humidity can increase, potentially reaching the dew point, at which point the relative humidity is 100%, and water vapor may condense into fog. This is particularly noticeable when hot air is used to dry something like your hair because hot air, having a higher capacity for water vapor, facilitates faster evaporation. Percent relative humidity can be mathematically defined as the ratio of the actual vapor density in the air to the saturation vapor density, multiplied by 100. This concept is closely related to the partial pressure of water vapor in the air, with 100% relative humidity occurring when the partial pressure is equal to the vapor pressure, indicating a saturation state where no additional water can enter the vapor phase.