6 Science Chapter 6 Changes Around Us

Chapter Notes and Summary
• We see a lot of changes in our surroundings. They may be caused by human beings, nature or animals.
• These changes may be temporary or permanent and may be periodic or non-periodic. changes may be slow or fast, reversible or irreversible.
Changes : Changes around us can be grouped as those that can be reversed (reversible change) and those that cannot be reversed (irreversible changes).
Examples of some reversible changes : Folding of a paper; rolling out a chapatti from a ball of dough; stretching of rubber to its normal size; melting of ice candy.
Examples of some irreversible changes : Ripening of fruits; souring of milk; cooking of food; sawing of a piece of wood; cutting of paper; burning of paper.
A change can occur by heating a substance. For example : iron blade, when heated, becomes slightly larger in size (expands) and when cooled down, contracts (contraction).
• Heating (or melting) of wax is a reversible change and burning of candle is an irreversible change.
• A change in which physical properties of a substance change but there is no change in its chemical composition is called a physical change.
• Most of physical changes are reversible. e.g., melting of ice, glowing of an electric bulb etc.
• changes that result in formation of new substances with different chemical properties are called chemical changes.
• Most of chemical changes are permanent and irreversible. e.g., digestion of food, ripening of of food etc.

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