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जन्म तिथि*: CALCULATE
by Nikunj

## 19 August 2018

### NCERT STD 6 SCIENCE CHAPTER 6 CHANGES AROUND US ONLINE MCQ TEST

What are the things you would want to change?
We do not have magical powers, of course. But, we can still change a few things around us, perhaps many things. Can you list a few things you can change around you, with no magic involved?
Many changes are taking place around us on their own. In the fields, the crops change from time to time. Sometimes, leaves fall from trees, change colour and dry out. The flowers bloom and then wither away. Are any changes happening in your body? Your nails grow, your hair grows, you grow taller and your weight increases as you grow. Did you realise earlier that so many changes are taking place around you all the time?
Can some of the changes be grouped together?
How can we group various changes? It might help, if we find some similarities between them.

## 6.1 CAN ALL CHANGES ALWAYS BE REVERSED?

Activity 1 Take a balloon and blow it. Take care that it does not burst. The shape and size of the balloon have changed (Fig. 1). Now, let the air escape the balloon.

Fig. 1 A balloon changes its size and shape on blowing air into it
Activity 2 Take a piece of paper and fold it as shown in Fig. 2. You have changed the sheet of paper into a toy aeroplane. You may have lots of fun in flying this plane. Once you are tired of it, unfold the paper again.

Fig. 2 A toy aeroplane made by folding paper
Activity 3 Take some dough and make a ball. Try to roll out a roti (Fig. 3). May be you are not happy with its shape and wish to change it back into a ball of dough again.

Fig. 3 A ball of dough and a rolled out roti
Now, think about the three changes you observed in Activity 1, 2 and 3. What do they have in common?
Was it possible to get the balloon back to its original shape and size?
Was the size of the paper same as before and after making an aeroplane?
Was it possible to get back the ball of dough again?
What do you conclude? In each of the three activities, is it possible to get back to the material with which we started our activity? If the answer is yes, it means that the changes occurring in these activities can be reversed. Now, let us repeat the same activities with a difference.
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. Oops! It burst.
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. 4)

Fig. 4 An aeroplane cut out of paper
Activity 6 Roll out a roti from the ball of dough again and bake it on a tawa

Fig. 5 A roti
We see that, the changes which have occurred in the Activity 4, 5 and 6 can not be reversed.
You use a pencil and an eraser. With repeated use, their shape and size changes. Can we reverse this change?
You must have seen a potter working on his wheel. He shapes a lump of clay into a pot. Can this change be reversed? He then bakes the pot in an oven. Now, can this change be reversed?
Some common changes are given in Table 1. Which of these changes, do you think can be reversed?
We find that one way we can group changes is to see if they can be reversed.