Page 21 - Understanding NCERT Science 09

What happens when you pour some Why do we see water droplets on the outer
acetone (nail polish remover) on your palm? surface of a glass containing ice-cold
The particles gain energy from your palm or water?
surroundings and evaporate causing the palm Let us take some ice-cold water in a
to feel cool. tumbler. Soon we will see water droplets on
After a hot sunny day, people sprinkle the outer surface of the tumbler. The water
water on the roof or open ground because vapour present in air, on coming in contact
the large latent heat of vaporisation of water with the cold glass of water, loses energy and
helps to cool the hot surface. gets converted to liquid state, which we see
Can you cite some more examples from as water droplets.
daily life where we can feel the effect of cooling
due to evaporation? uestions
Why should we wear cotton clothes in
summer? 1. Why does a desert cooler cool
During summer, we perspire more Q better on a hot dry day?
because of the mechanism of our body which 2. How does the water kept in an
keeps us cool. We know that during earthen pot (matka) become cool
evaporation, the particles at the surface of during summer?
the liquid gain energy from the surroundings 3. Why does our palm feel cold
or body surface and change into vapour. The when we put some acetone or
heat energy equal to the latent heat of petrol or perfume on it?
vaporisation is absorbed from the body 4. Why are we able to sip hot tea or
leaving the body cool. Cotton, being a good milk faster from a saucer rather
absorber of water helps in absorbing the than a cup?
sweat and exposing it to the atmosphere for 5. What type of clothes should we
easy evaporation. wear in summer?

What

you have

learnt

• Matter is made up of small particles.
• The matter around us exists in three states—solid, liquid
and gas.

• The forces of attraction between the particles are maximum in
solids, intermediate in liquids and minimum in gases.

• The spaces in between the constituent particles and kinetic
energy of the particles are minimum in the case of solids,
intermediate in liquids and maximum in gases.

10 SCIENCE

Rationalised 2023-24