changes around us class 6

 CHANGES AROUND US

Have you observed nature? Can you list out some changes that are happening around you?

We can see the change in season, growth of a plant from a sapling, boiling water, flowers blooming, and many more like that when you observe.We need to classify the changes into different groups.

changes around us class 6

melting of ice

boiling water

Some changes happen very slowly and some are fast. The growth of a plant is a slow change, but the burning of a paper is fast change. Some changes are desirable and some are not. Milk changing to curd is desirable, but milk getting spoiled is undesirable.  Some changes can be reversed and some cannot be reversed. Many changes are physical changes and many are chemical changes.

REVERSIBLE AND IRREVERSIBLE CHANGES

balloons

A balloon changes its size and shape on blowing air into it. If you let the air escape, it will come back into its original shape. Hence it is a reversible change.

Similarly, on unfolding a paper boat, we will get the paper in the same shape and size.

paper boat

If you take an ice cube and melt it, how will you get it back? We can bring it back by freezing. The same is the case with boiling water. Evaporated water vapor will condense back to the water. Hence all these changes are examples of reversible changes.

Let's see a few more changes.

dough

Make a ball with the dough and roll out a roti. Maybe you are not happy with its shape. We can bring it back to the ball of dough. This is a reversible change. But if you are baking the roti on a pan, are you able to get back the dough again? So the second one is not a reversible change. We can observe many irreversible changes in our daily life. 
Change of milk to curd, boiling of an egg, burning of paper, growth of a plant- these are all irreversible changes.
A change in which we can get back the same material in the same state is called a reversible change.
A change in which material changes into another form and cannot be brought back is called an irreversible change.

WAYS TO BRING A CHANGE

1. By heating

2. By cooling

3. By burning

4. By adding other things

blacksmith making tools

In the picture, you can see how a blacksmith makes a tool. He uses the principle of expansion and contraction to fix the handles of these tools. On heating, the metal expands, and on cooling, it contracts.

burning candle

We have observed the burning of a candle. Do you get the same amount of wax when it burns? The length of the candle decreases as it burns and it forms water vapor and carbon dioxide which are gases and it escapes into the atmosphere. Hence burning of a candle is an irreversible change. 
But on melting a piece of wax, we can bring it back by cooling. So melting of wax is a reversible change.
On adding a spoon of salt to the water, the dissolved salt can be obtained by evaporating water.
There must be many other ways of changing things around us. So we have discussed changes that can be reversed and change that cannot be reversed.