CHANGES AROUND US | SPEED NOTES | SCIENCE | CBSE | CLASS 6

Change in position, sunrise and sunset. Change in colour , sky at night and day time. Change in shape. ,look at themoon. Change in size,a seed germinate. Change in temperature, hot summer and cold winter. Change in state or form , water on cooling and heating. Rusting of iron. Everything around us is undergoing a change. Change is a continuous process. Some changes canbe reversed andsome cannot bereversed. A change may occur byheating a substance or by mixing it with someother. (a) Reversible change: A change in which theinitial substance canbe obtained backby reversing the action. Example: folding of paper, dissolving sugar inwater, etc.

CBSE Class–VI Subject Science Revision Notes CHAPTER – 6 Changes Around Us

COMMON CHANGES TAKING PLACE INNATURE Types of changes: (b) Non-irreversible change: Change in which theinitial substance cannot be obtained back by reversing the action. Example: burign of paper, grinding grains etc. (c) Physical change: Changes in the formof substance butnot in chemical identity. No new substance formed. Changes is sometimes reversible. Example: breaking a log ofwood. (d) Chemical changes: Changes inwhich substance istransformed into newsubstance. Initial substance is lost. Change is always irreversible. Example: burning alog of wood.

Air can becompressed by applying pressure. pressure maychange the shape of the object. Ways bywhich changes occur: (a) Boiling and Condensation: (i) Boiling: The rapid vaporization of a liquid when it isheated to itsboiling point. (ii) Condensation: The change of water vaporinto liquid wateron cooling. (b) Heating of metal: Process in which a metalis heatedto a certain temperature and thecooled in a particular manner to alter itsinternal structure forobtaining desired degree of physical and mechanical properties such as brittleness, hardness, and softness. (c) Freezing and Melting: (i) Freezing: Theprocess in whicha liquid turns into solid whenits temperature islowered. (ii) Melting: Theprocess in whicha solid converts to a liquid by applying heat. (d) usingpressure to change things