7. Experiments with Water

What floats - what sinks?

Ayesha was waiting for dinner. Today Ammi was making her favourite food - puri and spicy potatoes.

Ayesha watched as her mother rolled out the puri and put it in the hot oil. She saw that at first the puri sank to the bottom of the pan. As it puffed up, the puri came up and started floating on the oil. One puri did not puff up and did not float like the others. On seeing this, Ayesha took some dough and rolled it into a ball. She flattened it and put it in a bowl of water. Alas! it sank to the bottom and stayed there.

Think what would happen if

• Ayesha put a puffed puri in a bowl of water. Would it sink or float?
• You put a steel plate on water. Would it sink or float? What would happen to a spoon?
• Would the cap of a plastic bottle sink or float on water?

In the evening Ayesha went for a bath. She had just come out when her mother called, "Ayesha, you have dropped the soap in the water again. Take it out and put it in the soap case." Ayesha was in a hurry and the soap case fell out of

 

 

 

her hands. It started floating on water. Ayesha gently put the soap in the soap case. She saw that the case continued to float, even with the soap in it.

Have you seen that some thing float on water while others sink? Think how this happens! The poem here raises such questions.

Do this and find out

Do this experiment in groups of four friends. Each group will need a big pot filled with water and the things listed in the table. Put each thing one-by-one in water and observe. Write your observations in the table given on the next page.

Mark [✓] for the things that float. Mark [✕] for those that sink.

 

Find out from the other groups which things floated and which

sank in the water?

After doing the experiment, fill in the blanks.

 

1. The iron nail ______ in water but the katori ______. I think this happened because _________________________________
2. The empty plastic bottle ______ on water. The bottle filled with water ______ because ______________________________
3. The aluminium foil ______ when it was spread out. When pressed tightly into a ball it __________. This may have happened because ________

Is it magic?

When Ayesha woke up in the morning, Ammi had fever. Abbu made some tea and went to give medicines to Ammi. He told Ayesha, "You boil eggs. Also put some salt in the water." Ayesha took water in a pot. By mistake she put too much salt in the water. She saw the eggs at the bottom of the pot come up a little and start to float in water!

 

• Take some water in a glass. Put a lemon in it. Now keep putting salt in the water, half-a-spoon at a time. Were you able to float your lemon in water?
• What do you think, the lemon floated in salty water.

because......

What dissolved, what did not?

On Sunday Ayesha's cousin brother Hamid came to her house to play. As soon as he came he asked his aunt to make his favourite shakkarpara (a sweet dish). Ammi said, "Let me come back from the market, then I will make some for you. Why don't you help me? Take two glasses of water and put a bowl of sugar in it. Mix it till it dissolves." Hamid thought, "Let me finish this work fast. Then I will watch TV".

• Suggest some ways to Hamid for quickly dissolving sugar. 

Do this experiment 

Make groups of four friends. For the experiment you will need 4-5 glasses or bowls, spoons, water, and the things listed in the table. Take some water in each glass. Now try to dissolve one thing in one glass. Observe what happens and note in the table.

Tell

• Could you see the salt after it dissolved in water? If no, why?
• Does that mean that now the water does not have salt?

If it has, then where is the salt?

• What difference did you see – in the water with salt, and the water with chalk powder – after keeping for sometime?
• Which of the two would you be able to separate from the water by straining with a cloth – salt or chalk powder?

While doing the experiment Ayesha and Hamid had an argument. Ayesha felt that after stirring it, the oil dissolved in water. Hamid did not agree. He said, “Look, the tiny yellow oil drops can still be seen in the water”. Ayesha said, “Let’s wait for sometime and then see.”

• Do you think the oil got dissolved in the water? Why do you think so?

 

Racing drops 

Ayesha put two drops of oil on the lid of her tiffin box. Next to that she put two drops of water and two drops of sugar solution. She tilted the lid. She saw some drops slid down quickly, while some were left behind.

• You also try to do the same and then tell – which drop went ahead?

Why did it slide faster? 

Where did the water go?

One day Ayesha’s mother put some water to boil on the stove for making tea. She got busy with something and forgot about it. When she remembered and came to check, she found very little water left in the pan.

• Think where did the water go?
• Why did Chittibabu and Chinnababu keep their mango jelly in the sun?
• At your house, what things are made by drying in the sun?