Wet one hand with water and leave the other dry. Blow air across both hands and feel the cooling effect. Find out the reasons for it.
When you blow air across both hands, the wet hand feels cooler than the dry hand.
This happens because the water on the wet hand evaporates due to the air movement. The chapter explains that evaporation causes a cooling effect. When water evaporates from the skin surface, it absorbs heat from the skin, making it feel cooler.
The dry hand does not have any water to evaporate, so it does not experience this cooling effect.
The moving air from blowing increases the rate of evaporation, making the cooling effect more noticeable. This is similar to how fans make us feel cooler by increasing air movement over our sweat-covered skin.
Explanation
The chapter explains the cooling effect of evaporation on page 14: 'Water seeps through the surface of the earthen pot and evaporates, which imparts a cooling effect on the water.' On page 13, it states that 'with the increase in the movement of air, water evaporates faster.' When we blow air across a wet hand, the increased air movement speeds up evaporation, and the heat absorbed during evaporation causes the cooling sensation.
Solution Steps
Observation: The wet hand feels cooler than the dry hand when air is blown across both.
Cause: Water on the wet hand evaporates due to the air movement.
Mechanism: Evaporation absorbs heat from the skin surface, causing a cooling effect.
Contrast: The dry hand has no water to evaporate and therefore feels no cooling effect.
Factor: Moving air increases the rate of evaporation, enhancing the cooling.
Analogy: This process is similar to how fans cool sweat-covered skin.