Q1.
When water evaporates, it causes a cooling effect. If the amount of water in the air is already high (more humidity), water evaporates slowly. That is typically the case on a rainy day.
Answer
These two facts from Grade 6 Science are the key to the whole of humidity.
- Evaporation cools. When water turns into vapour it takes heat away from the surface it leaves. That is why sweat cools your skin, why an earthen matka keeps water cold, and why a wet floor feels cool underfoot.
- Damp air slows evaporation. Air can only hold so much water vapour. If it is already nearly full, very little more can evaporate into it — so wet clothes stay wet and sweat stays on your skin on a rainy day.
Dry air (low humidity) → fast evaporation → strong cooling → you feel comfortable
Damp air (high humidity) → slow evaporation → little cooling → you feel sticky and hot
Damp air (high humidity) → slow evaporation → little cooling → you feel sticky and hot
Why this explains ‘relative’ humidity: Air with no water vapour at all is rated 0% (impossible in nature), and air completely saturated with vapour is 100%. So relative humidity is really a measure of how full the air already is — and therefore of how much more it can still take from your wet clothes, your skin, or a farmer's soil.
Check it yourself: Wet the back of your hand and blow on it. It feels cold, because you are speeding up evaporation. Try it again on a very humid day — the cooling is far weaker.