Changes Around Us-Revision Notes

CBSE Class–VI Subject Science
Revision Notes
CHAPTER – 6
Changes Around Us
  • Everything around us is undergoing a change.
  • Change is a continuous process.
  • Some changes can be reversed and some cannot be reversed.
  • A change may occur by heating a substance or by mixing it with some other.
COMMON CHANGES TAKING PLACE IN NATURE
  1. change in position , sun rise an set.
  2. change in colour , sky at night and day time.
  3. change in shape. , look at the moon.
  4. change in size, a seed germinate.
  5. change in temperature, hot summer and cold winter.
  6. change in state or form , water on cooling and heating.
  7. rusting of iron.
Types of changes:
(a) Reversible change: A change in which the initial substance can be obtained back by reversing the action. Example: folding of paper, dissolving sugar in water, etc.
(b) Non-irreversible change: Change in which the initial substance cannot be obtained back by reversing the action. Example: burign of paper, grinding grains etc.
(c) Physical change: Changes in the form of substance but not in chemical identity. No new substance formed. Changes is sometimes reversible. Example: breaking a log of wood.
(d) Chemical changes: Changes in which substance is transformed into new substance. Initial substance is lost. Change is  always irreversible. Example: burning a log of wood.
Ways by which changes occur:
(a) Boiling and Condensation:
(i) Boiling: The rapid vaporization of a liquid when it is heated to its boiling point.
(ii) Condensation: The change of water vapor into liquid water on cooling.
(b) Heating of metal: Process in which a metal is heated to a certain temperature and the cooled in a particular manner to alter its internal structure for obtaining desired degree of physical and mechanical properties such as brittleness, hardness, and softness.
(c) Freezing and Melting:
(i) Freezing: The process in which a liquid turns into solid when its temperature is lowered.
(ii) Melting: The process in which a solid converts to a liquid by applying heat.
(d)  using pressure to change things
  • Air can be compresse by applying pressure.
  • pressure may change the shape of the object.