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Changes occur in our surroundings every day; now, we shall study the nature of these changes.
The day and night formation, the flowering of a bud, evaporation, condensation, curd formation, burning of woods, melting of ice etc., are some of the changes that occur around us. The changes are of two kinds, physical changes and chemical changes.
Seasonal changes
Example:
Day turns to night, growing crops in the agricultural field, falling leaves from trees, blooming of flowers, etc.
Changes in the human body: Some of these changes in the human body may occur in a minute or even in a year, and also they can be unnoticeable.
Example:
The growth of nails, hair, ageing, increasing height and weight, etc,.
Ageing
Change:
Change is constant. A process in which a substance becomes a different one from what it was earlier. It is the difference between the initial and the final state of any substance. The difference in the size or shape of an object is termed as a 'change'.
Life cycle of a butterfly
Physical and chemical change
The changes around us can be generally classified into two main types: Reversible change and irreversible change.
Reversible change: The changes that can be reversed to form their original shape and size are reversible changes
Example:
The stretching of a rubber band, freezing of water, melting of ice, inflation of a balloon, and folding of paper, etc.
Inflated and deflated balloon
2. A toy ship is made by folding a sheet of paper. When unfolded, it comes to its original shape as before.
Paper ship
3. A dough is made into a ball and rolled it out into a roti. If its shape is not good, it can be changed back into a ball of dough.
Dough
In all the above examples, the substances are reversed back into their original form.
Physical change: In the physical transformation, only the physical properties such as colour, structure, size are changed. No new substances are formed, and they are reversible in nature.
Melting of ice cubes
Example:
The glass is filled with \(100g\) of ice cubes. When ice is melted, it gives \(100g\) of water. Here, physical change takes place with a change in state. We call it physical change because we can again bring water to the ice by freezing it.
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