Goa Board Class 6 Solutions for Science – Changes Around Us (English Medium)
Page No. 51:
Question 1:
To walk through a waterlogged area, you usually shorten the length of your dress by folding it. Can this change be reversed?
Solution:
Yes, because the folded portion of the dress can be unfolded. It is a reversible physical change.
Question 2:
You accidentally dropped your favourite toy and broke it. This is a change you did not want. Can this change be reversed?
Solution:
No, this change cannot be reversed. But, breaking of toy does not bring any change in the composition of the toy. Some physical changes are irreversible but they do not bring any change in the composition of material.
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. | Change can be reversed or not | Yes/ No |
1. 2. 3. 4. 5. 6. |
The sawing of a piece of wood
The melting of ice candy Dissolving sugar in water The cooking of food The ripening of a mango Souring of milk |
Solution:
Physical changes can be reversed but chemical changes cannot be reversed.
S.No. | Change can be reversed or not | Yes/ No |
1.
2. 3. 4. 5. 6. |
The sawing of a piece of wood
The melting of ice candy Dissolving sugar in water The cooking of food The ripening of a mango Souring of milk |
No
Yes Yes No No No |
Question 4:
A drawing sheet changes when you draw a picture on it. Can you reverse this change?
Solution:
If we draw a picture on a drawing sheet with a pencil, we can get back the original drawing sheet by erasing the drawing with an eraser. In this case, the change can be reversed.
However, if we draw with a pen, then the original drawing sheet cannot be obtained back because we cannot erase ink. Hence, in this case, the change cannot be reversed.
Question 5:
Give examples to explain the difference between changes that can or cannot be reversed.
Solution:
To explain the differences between changes that can or cannot be reversed, some examples are given below:
(i) If we inflate a balloon, the size and shape of the balloon undergoes a change. However, the original size and shape of the balloon can be obtained back by allowing the air to escape from the balloon. This means that the change that occurs by inflating a balloon can be reversed. But, if the balloon bursts after being inflated, then its original size and shape cannot be obtained back. Thus, in this case, the change cannot be reversed.
(ii) If we fold a piece of paper, then the shape and size of the paper undergoes a change. In this case, the original shape and size of the original paper can be obtained back. Thus, this change can be reversed. However, if we cut the piece of paper, the change in the shape and size of the paper cannot be reversed.
(iii) After we roll out a chapatti from a ball of dough, the chapatti can be converted back into a ball. Thus, the change occurring here can be reversed. But, if we cook the chapatti on a tawa, then it cannot be converted back into a ball of dough. Thus, the change is irreversible.
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?
Solution:
No, the change in POP can not be reversed because on addition of water, it changes to another substance which on drying becomes hard.
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?
Solution:
No it can not be reversed.