- Books Name
- CBSE Class 6 Science Book
- Param Publication
- CBSE Class 6
Changes Caused by heating
(1) Some objects simply get hot, but no other changes take place.
When you drink hot milk or coffee from a cup you may feel that the cup gets hot however, no change in the state of the cup take place.
(2) Some object get hot and expand.
eg. Metal key on heating got hot as well as increased in size.
(3) Some object get hot and their shape and size changes.
eg. When the candle is lighted it starts burning. Its shape a nd size also changed.
(4) Some of the object shows change in their state.
eg. Ice is heated it change into water and on further heating changes into steam. All these changes can be reverse.
Again the metal rim is made slightly smaller than the wooden wheel. On heating, the rim expands and fits onto the wheel. Cold water is then poured over the rim, which contracts and fits tightly onto the wheel.
Cart wheel with metal rim fixed to it
CHANGES CAUSED BY PRESSURE OR FORCE
When you force into a balloon by applying pressure of your lungs, the shape and the size of the balloon changes. If you continue inflating the balloon with more air, a stage comes when the balloon burst and its shape changes again.
Metals can be hammered into thin sheets. The gold and silver leaves are prepare by gently hammering the small pieces of these metals with wooden handles.
eg. Stretching of rubber bands, spinning of cotton fibres
CHANGES CAUSED BY DISSOLVING
Substances, such as common salt, sugar, copper sulphate crystals etc. are soluble in water. During the process of dissolving a change is brought in the soluble substance.
Equal amounts of all soluble substances do not dissolve in any fixed amount of water.
However with the rise in temperature of water, more amount of substance dissolves in it.
1. Changes : Many changes are taken place around us on their own, e.g., flowers bloom and then wither away. We can also bring a change, e.g., change in the size of a ballon by blowing air in it.
2. Contraction : A process in which an object becomes smaller or shrinks is called contraction.
3. Evaporation : A process in which liquid changes into vapour is called evaporation.
4. Expansion : A process in which an object becomes bigger in size, e.g. metals expand on heating.
5. Melting : A process in which a solid melts to become a liquid on heating is called melting.