NCERT Class 7 Science Curiosity Chapter 05 Changes Around Us Physical and Chemical PDF Download

Chapter 5: Changes Around Us: Physical and Chemical

I placed a cube of ice here half an hour ago. It has now become water!

The bottle containing cold water is not cold anymore.

A bud that I saw yesterday on this rose plant has become a flower today.

Yesterday, I saw some brown spots on a banana, but today it has more brown spots and a strong smell.

These students are describing some changes. What kinds of changes are they talking about?

Activity 5.1: Let us think and reflect

You might have observed various changes happening around you. Some of them are listed in Table 5.1, you may notice that something is changing in each case. Take a moment to reflect on the changes in each case. Record your observations in Table 5.1.

You might have noticed that these changes could be in the size, shape, smell, or other property of the substance or object. Can you think of some other changes that happen in your surroundings? Make a list of those changes too.

We observe the changes occurring around us with the help of our senses of sight, smell, touch, hearing, and taste.

Can we arrange these changes into categories?

Let us try to answer this question.

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

Activity 5.2: Let us create and discuss

A. Creating some objects with paper

• Take a few sheets of paper and fold them to create new objects (Fig. 5.1).
• Do you get the same paper back when you unfold these objects?

[Figure 5.1: Objects made from paper, See in your textbook]

B. Playing with a balloon

• Take a balloon and inflate it. Now, loosen your grip and let the air escape out.
• Do you get the uninflated balloon back?
• Take another balloon; inflate it and grip the opening tightly. Now, prick it with a pin.

Caution - Be careful while using a pin.

• What happens? Will you be able to get the uninflated balloon back?

C. Crushing a piece of chalk

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

Is there any similarity in the changes listed in A, B, and C?

During all these changes, materials, such as the paper, the rubber sheet of the balloon, and the chalk, remained the same, though their appearances (shape or size) may have changed. You may also recall from the Grade 6 Science textbook Curiosity that water can exist in different states (solid, liquid, and gas), and can change from one state to another.

In all these cases, although we observe a change in the appearance, no new substance is formed. Such changes in which only physical properties like shape, size, and state of substances change are called physical changes.

Teacher's Note

Think about the key difference: when you fold paper into a plane, the paper itself is still there. When you crush chalk into powder, you still have chalk - just in a different form. The substance does not become something new. This is the main test of a physical change: can you theoretically reverse it, and is the material fundamentally the same?

Let us explore a different type of change.

Key Points

• Changes happen all around us in size, shape, smell, and other properties of materials and objects.
• We observe changes using our senses of sight, smell, touch, hearing, and taste.
• Physical changes are changes where only the appearance alters but no new substance is formed - the material stays the same.
• Examples of physical changes include melting ice, folding paper, inflating a balloon, and crushing chalk.

This is a preview of the first 3 pages. To get the complete chapter, click below.