NCERT Solutions for Class 6 Science Chapter 6 Changes Around Us

1. To walk through a waterlogged area, you usually shorten the length of your dress by folding it. Can this change be reversed?

Answer: Yes, this change can be reversed. The length of the dress can be again increased 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?

Answer: No, this change cannot be reversed.

3. Some changes are listed in the following table. For each change, write in the blank column, whether the change can be reversed or not.

S.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	___

Answer:

S.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?

Answer: If drawing on the drawing sheet is drawn using pencil then, by erasing the drawing change can be reversed. In case, if drawing is made using paint or pen, then changes cannot be reversed.

5. Give examples to explain the difference between changes that can or cannot be reversed.

Answer:

1. Take a balloon and blow air in it. It can be observed that, shape of balloon changes by growing bigger in size. Now, it let the air in the balloon escape. It can be observed that balloon takes its initial shape. Thus, it is a reversible change. In case if balloon burst, then the change is irreversible.
2. Take a paper and make an aeroplane from it. Here, shape of paper is changed. One can obtain initial shape of paper by unfolding it. Thus, it is reversible change. In case, if paper is cut instead of folding it, then size of paper changes but this action cannot be reversed. Thus, it is irreversible change.
3. Take a ball of dough and make a chapati from it. Also, chapati can be rolled again to make a ball. Thus, this change is reversible. In case, if chapati is roasted on pan, then it cannot be rolled again to make ball of dough. Thus, it is an irreversible change.
4. Other examples –

Reversible	Non-reversible
Blowing air in balloon.	Cutting fruits into slices.
Filling empty container with milk.	Writing with pen on paper.
Detachment of all parts of electric fan.	Eating food.
Folding of paper.	Cutting paper.
Opening or closing of window.	Flour of grains.

6. A thick coating of a paste of Plaster of Paris (POP) is applied over the bandage on a fractured bone. It becomes hard on drying to keep the fractured bone immobilised. Can the change in POP be reversed ?

Answer: Once POP gets dry, it becomes hard and therefore, change in POP 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 cement, could be reversed ?

Answer: Due to rain, bag of cement gets wet and chemical change occurs in cement making it hard. Even if sun shines brightly, this change cannot get reversed. Thus, it is an irreversible change.

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