Mention the changes that can be reversed.

1) Blowing air into a balloon

2) Making a ship with paper

3) An aeroplane that is cut out from a paper

4) Melting of tar

5) Burning of candle

6) Batter to idli

7) Raw egg to boiled egg

8) Bud to flower

9) Milk to curd

10) Butter to ghee

Answers

1) Reversible

2) Reversible

3) Not reversible

4) Reversible

5) Not reversible

6) Not reversible

7) Not reversible

8) Not reversible

9) Not reversible

10) Not reversible

Answer the following questions

1) To walk through a water logged area, you usually shorten the length of your dress by folding it. Can this change be reversed?

It is reversible

2) You accidentally dropped your favourite toy and broke it. This is a change you did not want. Can this change be reversed?

This change is not reversible.

3. How can we fix iron rings on wooden handles?

If the iron ring is larger than the wooden handle in diameter, it will not fit perfectly and may come off frequently. To prevent this, the iron ring is made slightly smaller than the wooden handle. In order to fix the ring around the handle, the ring is heated and then it will expand slightly. This allows the wooden handle to easily pass through the ring. When the ring cools, it contracts and becomes small and fits perfectly on the handle.

4. How is a metal rim fixed on the wooden wheel?

The metal rim is slightly smaller than the wooden wheel in diameter. When the ring is heated, it expands and becomes slightly bigger than the wheel. This allows it to fit into the wheel. When cold water is poured on the rim, it cools and fits tightly on the wheel.

5. Briefly explain an activity to show changes both in burning of a wax candle and heating wax.

Take a candle and measure its length. Fix it at a suitable place and light it. Allow it to burn for a while and measure its length again. We can see that the candle has become shorter in length and it is not possible to reverse this change.

Take some wax in a pan and heat it. The wax will melt. Remove the heat source and allow the wax to cool. We can see that the wax has regained its previous form. Therefore this change is reversible.