Many changes happen around us that we can’t trace, just like magic.

In your garden, you see flowers blooming from their buds, grass growing even after being cut again and again, and ants making their home in the corner of the garden.
You find it hard to keep track of how and when a flower blooms. It can take a long time or happen in a second.

It might be easier if we could identify the types of change around us.
Let’s try to sort them by similarities.
If a change of an object can be reversed back to the original shape of the object, it is a reversible change. You can see it when you fold a paper, blow a balloon and play with a dough-ball.

If a change of an object is permanent and cannot be reversed back to its original form, it is irreversible. Try breaking a stick or bursting a balloon.

Can you give more examples from your daily activities at home?

Heat is a useful energy that we use every day.
A blacksmith heats up metal, makes the shape that he wants, and fits the handle to the metal. This happens because the metal expands and allows the blacksmith to give it a new shape. This change is therefore called expansion.
The blacksmith, then, lets the new metal cool down which allows it to remain in that shape permanently. This process is called contraction in which the metal shrinks at the heated area and becomes smaller.

There are more examples of tools that are made using contraction and expansion such as gardening tools, railway tracks, screwdrivers, cooking pans, etc.
Can you name a few more?

Yet, these are not the only reversible changes.
Heating water turns it into water vapour. This change is called water evaporation.
However, when we cool water using a cold surface or collect it in a cool vessel. The water vapors change back to a liquid state called condensation.
Both evaporation and condensation are reversible changes.
When you burn a candle and when you take ice outside the freezer, you are helping them change from solid form to liquid. This is called melting- another reversible change.

When your mom cooks, she changes the shape of ingredients to make different dishes. The powder spice mix you have at home, the curd made from milk, ice cream, etc.

Which one of these is the most useful change to you?

Coming back from school today, were you worried about tomorrow’s exam on the chapter- Changes Around Us from your Class 6 NCERT Science textbook?
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