To make the grains fit for cooking and eating. Stones and husk are not useful and can harm us. Picking them out by hand is called handpicking.

• Sieving: the small chana dal falls through the holes; the big puffed rice stays on the sieve.
• Winnowing: the light puffed rice is blown away; the heavier dal falls down.

• The thin skins come off the peanuts.
• When we blow, the light skins are blown away, and the heavier peanuts stay.
• So blowing air separates the lighter part from the heavier part.

• Farmers use winnowing with a soop (bamboo tray).
• No, they do not fall at the same place. The heavy grains fall straight down, close to the farmer.
• The light husk is blown away by the wind and falls farther.
• Yes, the wind can separate the two parts.

• She can winnow in front of a fan or a cooler, blow air herself, or go outside where there is wind.
• At home, rice, dal and ragi are cleaned with a soop, and we blow away the skins of roasted peanuts.

• Yes, all the holes of a sieve are about the same size.
• No. If the holes are bigger than all the particles, everything passes through and nothing is separated.
• Yes. Particles smaller than the holes pass through; bigger particles stay on the sieve.

Yes. Workers throw sand against a big, slanting wire sieve. Fine sand passes through, and pebbles and stones are left behind.

• Sabarmati Ashram in Ahmedabad was Mahatma Gandhi’s home for many years.
• In 1930, Gandhiji began the Dandi March (Salt Satyagraha) from here, walking to Dandi on the sea coast.
• It was organised against the British tax on salt. At Dandi, Gandhiji made salt from sea water to break the unfair law.

Sambhar Lake (Rajasthan), Chilika Lake (Odisha), Pulicat Lake (Andhra Pradesh–Tamil Nadu), Pangong Tso (Ladakh), and the Rann of Kutch salt marsh (Gujarat). The seas around India also give us salt.

• Yes, white patches appear. They are salt; you can feel it by touching.
• The water has evaporated into the air.
• Sweat has salt in it. When sweat dries (evaporates), the salt is left on clothes as white patches.

• Salt is left in the china dish. Yes, we get the salt back.
• To get both, boil the salt water and cool the steam on a cold lid or plate. The steam turns back into water drops, which we collect.
• The processes are evaporation and condensation.

Decantation. Leave the mixture still. Oil floats on top as a layer. Gently pour off the oil, or take it out with a spoon.

• No. Mud particles are much smaller than the holes of a strainer, so they pass through.
• Cloth has very small gaps between its threads, so it stops more mud.
• More layers of cloth (about 4 or more) give clearer water, but the finest mud may still pass. Filter paper has even smaller pores and gives clearer water.

• No, the mud particles do not pass through.
• Mud stays on the filter paper as residue.
• Clear water, the filtrate, collects in the conical flask.

1. Cut a plastic bottle in half. Turn the top half upside down, with the cap removed.
2. Put cotton or a cloth piece at the neck.
3. Add layers in this order: charcoal, fine sand, coarse sand, then small pebbles on top.
4. Pour the pond water slowly on top and collect the clearer water below.

The water is clearer, but boil it before drinking.

Sample lines (write your own too!):

Bottles and wrappers float everywhere,
Our river home needs love and care.

Clean the banks and keep it pure,
A plastic-free river is the cure.

• Heat the sour milk. It splits into solid paneer (chhena) and a watery liquid (whey).
• Pour it through a muslin cloth: this is filtration. The paneer stays in the cloth.
• The leftover whey can be used in making dough or curry.

A mixer (blender / mixer-grinder).

Magnetic separation. Iron nails are attracted by the magnet; sawdust is not.

(ii) Sorting. We sort out the unwanted pieces by hand.

(iii) Cream from milk. Churning separates the light cream (butter) from milk or curd.

(iii) Pore size. The pores of the filter must be smaller than the particles to be removed.

• When the solid is heavy and settles quickly, like sand or stones in water, or when washing rice and dal.
• When there is a large amount of liquid, and filtering would take too long.
• When no filter is available, like pouring tea without a strainer.
• When separating two liquids that do not mix, like oil and water. Filtration cannot do this.

Yes, filtration. The hair in our nose acts like a filter. It traps dust, pollen and germs from the air we breathe, and lets clean air go into the body.

• Masks are made of layers of cotton cloth or special non-woven fabric (like polypropylene).
• They work as a filter. Their tiny pores let air pass, but stop droplets, dust and germs. This protects us and others.

1. Handpicking: pick out the big potatoes.
2. Dissolving: add water to the salt and sawdust and stir. Salt dissolves; sawdust does not.
3. Filtration: filter the mixture. Sawdust stays on the filter paper as residue; dry it.
4. Evaporation: heat or keep the salt solution (filtrate) in the sun. Water evaporates and salt is left.

1. Magnetic separation: move a magnet through it to take out the iron nails.
2. Handpicking: pick out the stones and black pepper (or use a sieve with holes that keep them back).
3. Sedimentation and decantation / filtration: sand settles down; pour off or filter the salt water. Sand stays as residue.
4. Evaporation: heat the salt water. Salt is left behind. To also get the water back, cool the steam (condensation).