❄️ 1.5.2 – How Does Evaporation Cause Cooling?

❄️ 1.5.2 – How Does Evaporation Cause Cooling?

🔍 What You Observe:

  • Your skin feels cold after applying perfume or alcohol.

  • Sweating cools your body.

  • Water in an earthen pot (matka) stays cooler than in a bottle.

But why does this happen? Let’s understand.

🔬 Scientific Explanation:

  • During evaporation, only the particles with the highest kinetic energy escape from the liquid surface into the air.

  • When these energetic particles leave, the average kinetic energy of the remaining particles decreases.

  • Since temperature is directly related to kinetic energy, the liquid's temperature drops.

  • This results in a cooling effect.

📘 Definition:

“Evaporation causes cooling because the particles that escape take away heat energy from the surface, lowering its temperature.”

🌡️ Real-Life Examples:

✅ 1. Sweat Cools the Body

  • Sweat evaporates from the skin.

  • It absorbs heat from your body → you feel cooler.

✅ 2. Alcohol / Perfume Feels Cold

  • Alcohol is highly volatile (evaporates quickly).

  • When applied on the skin, it takes away heat → gives a cooling effect.

✅ 3. Water in Earthen Pot (Matka)

  • Water seeps through the pores of the clay pot.

  • It evaporates on the outer surface, taking heat from the water inside → keeps it cool.

🧠 Key Concept Recap:

Process What Happens?
Evaporation High-energy particles escape as vapour
Energy Use Heat energy is absorbed from surroundings
Result Surface cools down → we feel a cooling effect

💬 Ask Your Students:

  1. Why do we feel cool after sweating?

  2. Why does water stay cool in a clay pot?

  3. Why is evaporation called a "surface phenomenon"?

🎤 Closing Line for Class:

“Evaporation doesn’t just change liquid into vapour — it quietly carries away heat, leaving behind a cool touch that you can feel every day, from your skin to your sip of matka water.”

Would you like this explanation converted into a diagram, flashcard, or interactive classroom demo (e.g., showing evaporation with alcohol)?

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