Class 6 Science NCERT Solutions for Chapter – 6 Changes Around Us

Changes Around Us

Question 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.

Question 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.

Question 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.ChangeCan 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.NoChangeCan be reversed (Yes/No)
1.The sawing of a piece of woodNo
2.The melting of ice candyYes
3.Dissolving sugar in waterYes
4.The cooking of foodNo
5.The ripening of a mangoNo
6.Souring of milkNo

Question 4.
A drawing sheet changes when you draw a picture on it. Can you reverse this change ?

Answer:
No

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

Answer:
There are several examples to explain the difference between changes that can or cannot be reversed, for example

(1) Take a balloon and blow it. The shape and size of the balloon will change. Now, let the air escape the balloon. The balloon comes back to its original position. But if we prick the filled ballon and burst it we can’t bring the balloon to its original position.

(2) Take some dough and make a ball. Try to roll out a roti, but if we are not happy with its shape we can again change it back into a ball of dough. But if we roll out a roti and bake it on a tawa, we can’t bring it back into a ball of dough.

Question 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:
No, it’s not a reversible change.

Question 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:
No, it’s not a reversible change.

InText Questions and Answers

Activity 1

We take a balloon and blow it. We take care that it does not burst. The shape and size of the balloon have changed (Fig. 6.1). Now, let the air escape the balloon.
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Activity 2

Take a piece of paper and fold it as shown in (Fig. 6.2). Change the sheet of paper into a toy aeroplane. Unfold the paper again.
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Activity 3

Take some dough and make a ball. Try to roll out a roti (Fig. 6.3). May be you are not happy with its shape and wish to change it back into a ball of dough again.
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Now answer the following questions :

Question 1.
Was it possible to get back the balloon in its original shape and size ?

Answer:
Yes

Question 2.
Was the size of the paper same as before and after making an aeroplane ?

Answer:
Yes

Question 3.
Was it possible to get back the ball of dough again ?

Answer:
Yes

Question 4.
What do you conclude?

Answer:
We conclude that in each of the three activities, it is possible to get back to the material with which we started our activity. Changes occuring in these activities can be reversed.

Activity 4

Take the same balloon, which you used in Activity 1. Blow it to its full size and tie its mouth with a string tightly. Prick it with the pointed tip of your pencil. It bursts.

Activity 5

Take the same piece of paper, which you used in Activity 2. Draw an aeroplane on it and cut along its outline (Fig. 6.4).
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Activity 6

Roll out a roti from the ball of dough again and bake it on a tawa (Fig. 6.5).
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Now answer the following questions :

Question 1.
Was it possible to get back the balloon in its original shape and size ?

Answer:
No

Question 2.
Was the size of the paper same as before and after making an aeroplane ?

Answer:
No

Question 3.
Was it possible to get back the ball of dough again ?

Answer:
No

Question 4.
What do you conclude ?

Answer:
We conclude that in each of the three activities, it is not possible to get back to the material with which we started our activity. Changes occuring in these activities can not be reversed.

Activity 7

Take a small candle and measure its length with a scale. Now fix it at a suitable place and light it. Let it burn for sometime. Now blow out the candle and measure its length again (Fig. 6.21).
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Question 1.
Can the change in the length of the candle be reversed ?

Answer:
No

Question 2.
If we take some wax in a pan and heat it then can this change be reversed ?
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Answer:
Yes

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