Physical changes

Activity 5.2 has three small tests:

• A. Fold paper into a boat or a hat. Unfold it. Is it the same paper? Yes.
• B. Blow up a balloon and let the air out. You get the flat balloon back. (Prick another one with a pin, carefully: it bursts, but the pieces are still rubber.)
• C. Crush a piece of chalk into powder. It is still chalk, just in a different shape.

What is the same in all three? The material stays the same: paper is still paper, rubber is still rubber, chalk is still chalk. Only the look, the shape or size, has changed.

Water is the same. Ice, liquid water and steam are all water, just in different states.

A change in which only physical properties like shape, size or state change, and no new substance is formed, is a physical change.

More examples: tearing paper, drying wet clothes, rolling a ball of dough into a chapati (it is still dough; you could squash it back), and dissolving sugar in water or making nimbu pani. The sugar is still there in the water: taste it, and if you let the water evaporate, the sugar is left behind.