NCERT Summary: Changes Around Us | NCERT Video Summary: Class 6 to Class 12 (English) - UPSC PDF Download

Introduction

• Changes can occur everywhere at any time.
• Change is a continuous process.
• Some changes are reversed and some cannot be reversed.
• Change may occur by heating a substance or by mixing it with some other substance.

Common changes taking place in nature

• Change in position, sun rise and set.
• Change in colour, sky at day and at night time.
• Change in shape, shape of moon.
• Change in size, a germinate seed.
• Change in temperature, hot summer and cold winter.
• Change in state or form, water on cooling and heating.
• Rusting of iron.

Types of changes

• Reversible changes
• Irreversible changes
• Chemical changes
• Physical changes
• Expansion And Contraction

1. Reversible changes

• It is an effect on substance in which substance get returned to its original state.
• The change only alters the physical state of the substance that means there is no new substance is formed.
  Examples: melting of ice, water turning into vapour, inflation of balloon etc.

2. Irreversible change

• In this process, the changes cannot be reversed are called irreversible changes.
• In irreversible changes new material being produced, which may or may not be useful.
  Examples: Ripening of fruits is an irreversible change because it is not possible to get back the raw fruits from ripened or mature ones.
• Blooming of flowers is an irreversible change because flowers cannot change back into buds.

3. Physical changes

• In this changes, there is no new substance is formed.
• It is reversible
  Examples: melting of wax, Melting of ice, crushing can etc.

4. Chemical change

• In this change there is a new substance is formed after the change.
• It cannot be reversed by simple physical means.
  Examples: rusting of iron, burning of candle etc.

5. Expansion and Contraction

• Some materials expand on heating and some material contract on cooling.
• The amount of expansion differs in solids, liquids, Physical change and gases.
• Gases material expands the most while solids material expands the least.
•  Solids material contract the least while gases material contract the most.

Causes of change

Force

• It can bring changes in certain thing. It can change motion, shape and size of objects by push or pull.
• Examples
  (i) When a potter applies force on a lump of soil, it gives shape to the lump.
  (ii) When a goldsmith hammers a piece of gold, he makes intricate designs on it.

Temperature

• This brings changes by causing increase or decrease in temperature.
• Examples
  (i) When ice is kept on room temperature, it melts and turns into water.
  (ii) When a candle begins burning, its wax start melts because of higher temperature.