Answer the following questions :
1. To walk through a water logged area, you usually shorten the length of your dress by folding it. Can this change be reversed.
Ans: Yes, the folded dress can be reversed by unfolding it.
2. You accidentally dropped your favourite toy and broke it. This is a change you did not want. Can this change be reversed.
Ans: No, the broken toy cannot be made whole. So it cannot be reversed.
3. Some changes are listed in the following table. For each changes, write in the blank column, whether the change can be reversed or not.
| Sr.no | Change | Can be reversed (yes/no) |
| 1 | The sawing of a piece of wood | |
| 2 | The melting of ice candy | |
| 3 | Dissolving sugar in water | |
| 4 | The cooking of food | |
| 5 | The ripening of a mango | |
| 6 | Souring of milk |
Ans :
| Sr.no | Change | Can be reversed (yes/no) |
| 1 | The sawing of a piece of wood | No |
| 2 | The melting of ice candy | Yes |
| 3 | Dissolving sugar in water | Yes |
| 4 | The cooking of food | No |
| 5 | The ripening of a mango | No |
| 6 | Souring of milk | No |
4. A drawing sheet changes when you draw a picture on it. Can you reverse this change.
Ans: A drawing sheet can be reversed when a pencil is used to draw a picture. When a pen or colour pencil is used, changes cannot be reversed.
5. Give examples to explain the difference between changes that can or cannot be reversed.
Ans:
Changes that can be reversed :
i) Water frozen into ice .
ii) Opening and closing a bottle .
iii) Soaking and drying of cloth.
Changes that cannot be reversed :
i) Clay baked into bricks .
ii) Trees as furniture’s .
iii) Flour / batter made into a cake.
6. A thick coating of a paste of Plaster of Paris(POP) is applied over the bandage on a fractured bone. It became hard on drying to keep the fractured bone immobilized. Can the change in POP be reversed.
Ans: No, the change cannot be reversed.
7. A bag of cement lying in the open gets wet due to rain during the night. The next day the sun shines brightly. Do you think the changes, which have occurred in the cements, could be reversed.
Ans: No, the change cannot be reversed because the wet cement become hard in the morning.
Suggested projects and activities:
1. Take a lemon, a paint brush and a piece of paper. Cut the lemon and squeeze out its juices in a cup. Dip the brush in the lemon juice and water a message on the paper. Let the paper dry and you find that the letters of your message become invisible. Now, press the paper with hot iron or warm it by holding it above the flame of a candle (Take care that it does not catch fire). As the paper gets warm, invisible letters changes into dack brown colour. Identify the changes that can be reversed.
Ans: Even after writing on the paper with lemon juice, the lemon juice becomes invisible and the paper becomes plain again.
2. Observe preparation of dishes at your home. Identify two changes that can be reversed.
Ans: The two changes that can be reversed are :
a) A used vessel can be cleaned again.
b) A hot dish cooked can be cooled, this process can again be repeated.
3. Maintain a record for one year of the season changes in vegetables, clothing, nature and events cannot be reversed .
(Students are recommended to try this question).