Class 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?
2.You accidentally dropped your favourite toy and broken. Can this change 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 or not | Yes/No |
| 1.
2. 3. 4. 5. 6. |
The sawing of piece of wood
The melting of ice candy Dissolving sugar in water The cooking of food The ripening of a mango Souring of milk |
- Drawing sheet changes when you draw a picture on it. Can you reverse this change?
- Give examples to explain the difference between changes that can or cannot be reversed.
- A thick coating of a paste of plaster of Paris(POP) is applied over the bandage on a fractured bone. It becomes hard on trying to keep the fractured bone immobilised. Can the change in POP be reversed?
- 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?
Answers:
Ans 1. Yes, this can be reversed.
Ans 2. No, it can not be reversed
Ans 3. If a picture is drawn on a drawing sheet with a pencil, the original drawing sheet can be obtained back by erasing the drawing with an eraser. While, if a drawing was drawn with a pen or watercolour, the original drawing sheet cannot be obtained back because erasing pen ink or watercolour with an eraser. So, in this case, the change cannot be reversed.
Ans 4.
1. The sawing of 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
Ans 5.
When a weight is suspended from a spring, the length of the spring increases. But the moment the weight is removed, the spring returns back to its original length. This is an example of reversible change. On the other hand, when a piece of coal is burnt it changes into smoke and ash. The piece of coal cannot be obtained back from smoke and ash so, it is an example of irreversible change.
Ans 6.
No, the change in POP cannot be reversed by using simple physical means because, on the addition of water, it changes to another chemical substance which on drying becomes hard. However, this change can be reversed using some chemical means.
Ans 7.
No, it cannot be reversed.