Class 7
Chapter 6 Class 7 - Physical and Chemical Changes

Change in size and shape

An activity to show change in size and shape:

  • Take a sheet of paper and cut it into pieces .
  • Now we cannot join the cut pieces of paper to make the original shape. 
  • But each small piece of paper is still paper ; it has not changed to something else. 
  • So this activity only changes the size and shape of paper. 
  • No new substances are formed.
  • So it is a physical change .

 

Change in colour

An activity to show change in colour:

  • Take a hacksaw blade and hold it with tongs . Keep the other end on flame
  • After sometime we see that tip of blade get healed and change to red in colour. 
  • Now remove the blade from the burner and allow it to cool
  • On cooling the tip, the colour returns to the original grey
  • Temporary change in colour of take saw blade has taken place on heating
  • No new substances have been formed
  • Hence, it is a physical change

 

Change in physical state of substances 

An activity to show change in physical state:

  • Take some ice in a tumbler and keep it in the sun
  • It changes into water .
  • On heating the water it changes into steam .
  • if we cool the steam we get water and on freezing the water we get ice .
  • We see that only the physical state has changed. 
  • No new substances have been formed.
  • So it is a physical change .

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Maninder Singh

CA Maninder Singh is a Chartered Accountant for the past 13 years and a teacher from the past 17 years. He teaches Science, Economics, Accounting and English at Teachoo