5.1 A Substance May Change in Appearance but Remain the Same!

What is a Physical Change?

It means a change where only the look of a substance changes.

The substance itself stays the same.

Examples

• Folding a paper into a plane.
• Crushing a piece of chalk into powder.
• Melting an ice cube into water.
• Cutting a vegetable into pieces.
• Boiling water into steam.

Key features of a physical change

• Only the appearance changes — shape, size, or state.
• No new substance is formed.
• The original substance is still there.
• Most physical changes can be reversed .

What are "Physical Properties"?

These are properties we can see or measure without changing the substance.

Three main physical properties that can change

• Shape
  • Example: a folded paper.
  • Example: a rolled chapati .
  • Example: a twisted wire.
• Size
  • Example: cut paper.
  • Example: chopped vegetables.
  • Example: crushed chalk.
• State
  • Solid to liquid: ice melting.
  • Liquid to gas: water boiling.
  • Gas to liquid: water vapour condensing.

Recall — The Three States of Water

Water can exist in three states .

The three states of water

• Solid — ice.
• Liquid — water.
• Gas — water vapour (steam).

How water changes state

• Water can change from one state to another.
• This happens by gaining heat or losing heat .
• All these state changes are physical changes .
• The substance is always H₂O.

👀 Activity 5.2 — Three Hands-On Demonstrations of Physical Change

Activity 5.2 — Let Us Create and Discuss

Part A — Creating Objects with Paper

• Take a few sheets of paper.
• Fold them to create new objects — a paper boat, plane, bird, frog.
• Now unfold the objects.
• Question: Do you get the same paper back?

Part B — Playing with a Balloon

⚠️ Caution — Be careful while using a pin.

• Take a balloon and inflate it.
• Loosen your grip and let the air escape.
• Question: Do you get the uninflated balloon back?
• Take another balloon, inflate it, and grip the opening tightly.
• Prick it with a pin.
• Question: What happens? Will you get the uninflated balloon back?

Part C — Crushing a Piece of Chalk

• Crush a small piece of chalk into powder.
• Question: Can you get the chalk piece back from the powder?

Observation

• Paper: When you unfold, you get the same paper back — reversible.
• Balloon (let air out): You get the uninflated balloon back — reversible.
• Balloon (pricked): The balloon bursts — you cannot get the whole balloon back — irreversible.
• Chalk: Powder cannot be reassembled into the original chalk piece — irreversible.

Explanation

• In every part — A, B, and C — the material itself remained the same : still paper, still rubber, still chalk.
• Only the appearance (shape or size) changed.
• So all of these are physical changes .
• Some physical changes are reversible (folding paper, deflating a balloon); some are not (bursting a balloon, crushing chalk).

→ A change can be a physical change even when it cannot be reversed — what matters is whether a new substance forms.

We have just seen physical changes. Now let us explore a different type of change — one where a new substance is formed.