Final answer:
Relative humidity measures water vapor in the air relative to the maximum possible at a given temperature. High relative humidity can inhibit evaporation, making us feel hotter, while low humidity may dry out mucous membranes. Changes in temperature affect relative humidity, as warmer air can hold more water vapor.
Step-by-step explanation:
Understanding Relative Humidity and Temperature
Relative humidity is a measure of how much water vapor is present in the air compared to the maximum amount it can hold at a specific temperature. When the relative humidity reaches 100%, the air is at saturation, and this can inhibit evaporation. As temperature decreases, like in the evening, relative humidity tends to rise, potentially reaching the dew point. At the dew point, fog may form due to the condensation of water droplets. When it comes to drying things, such as your hair, using hot air is more effective since hot air can hold more water vapor, accelerating the evaporation process.
On a muggy day with a relative humidity of 90% at 20°C, if the temperature rises to 30°C and the water vapor density remains constant, the relative humidity will actually decrease because warmer air can hold more moisture before reaching the point of saturation.
The phrase "it's not the heat, it's the humidity" encapsulates the discomfort felt due to inhibited evaporation of sweat from our skin, making us feel hotter even at the same temperature in high humidity conditions. Conversely, low humidity can lead to dry mucous membranes, possibly resulting in an increased risk of respiratory infections.