6th Chp 6 Notes

                          Class 6th Science Notes             

             Chapter 6 Changes Around Us            

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

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.

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.

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.

Chemical 

→ 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.

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.