Changes Around Us
Exercise:
1). To walk through a waterlogged area, you usually shorten the length of your dress by folding it. Can this change be reversed?
Yes, this change can be reversed.
2). You accidentally dropped your favorite toy and broke it. This is a change you did not want. Can this change be reversed?
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.
| Sr | 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?
No, we cannot reverse this change.
5). Give examples to explain the difference between changes that can or cannot be reversed.
| Reversible changes | Irreversible changes | ||
| 1 | Changes that can be reversed are called as reversible changes. | 1 | Changes that can not be reversed are called as irreversible changes. |
| 2. | The original size and shape of the substance can be obtained. | 2 | The original size and shape of the substance cannot be obtained. |
| 3 | Generally, physical changes are reversible changes. | 3 | Generally, chemical changes are irreversible changes. |
| 4 | eg. Stretched rubber comes to its original shape, Blowing of a balloon. | 4 | eg. Frying a puri, |
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 dying to keep the fractured bone immobilized. Can the change in POP be reversed?
No, the change in POP cannot be reversed as it is a chemical change.
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?
No, this change cannot be reversed.
Additional Questions:
Write whether True or False
1). Many changes are taking place around us on their own.
True.
2). On heating iron expands.
True.
3). It is possible to change water into ice.
True.
4). All the changes can be reversed.
False
5). Ice melts when heated.
True.
Classify the following as reversible and irreversible changes
Leaves fall from trees, frying puri, blowing of a balloon, making a paper aeroplane, growth of a plant, rolling out roti from the dough, burning of a match stick
| Reversible changes | Irreversible changes | ||
| 1 | blowing of a balloon | 1 | Leaves fall from trees. |
| 2. | making a paper aeroplane | 2 | frying puri |
| 3 | rolling out roti from the dough | 3 | growth of a plant |
| 4 | burning of a match stick | ||
Answer the following
1). How is the iron blade is fixed to the wooden handle?
The iron blade of the wooden handle has a ring in which the wooden handle is fixed. Normally, the ring is slightly smaller in size than the wooden handle. To fix the handle, the ring is heated and it becomes slightly larger in size. Now, the handle easily fits into the ring. When the ring cools down it contracts and fits tightly onto the handle.
Fill in the blanks.
1). On heating the water changes into its vapour.
2). Ice melts on heating
3). Some changes can be reversed and some cannot be reversed
4). A change may occur by heating a substance or by mixing it with some other.
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