Theory:

Change is constant. A process in which a substance becomes different one from what it was earlier.
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Ageing
  
Change 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 'change'.
 
Change is the Law of Nature:

We notice various changes in our day-to-day lives.
 
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Seasonal changes
Example:
Weather changes on a regular basis (daily/seasonally). A paper burns quickly; however, an iron nail takes a few days to corrode. Milk takes several hours to turn into curd, yet vegetables soften in just a few minutes when cooked.
Shape, colour, temperature, position, and composition all vary due to the modifications described above. Some changes are visible, while others are difficult to detect.
 
Classification of changes:
  
There are numerous types of changes that take place in the natural world around us. Some changes occur immediately, while others take hours, days, or even years. Some changes are only temporary, while others are long-term.
 
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Types of changes
  
Some alterations result in the formation of new compounds, while others do not. Some changes occur naturally, while humans cause others. Finally, some changes are beneficial to us, while others are not.
 
We will now categorise modifications based on key similarities and contrasts:
  • Slow and Fast changes
  • Reversible and Irreversible changes
  • Physical and Chemical changes
  • Desirable and Undesirable changes
  • Natural and Man-made changes