GSEB Solutions for Class 6 Science and Technology – Changes Aroun Us (English Medium)
The changes which are brought about nature itself are called natural changes. These changes are beyond the control of man.
Example: Change of season, Tides in the sea, Ageing of plants, Landslides etc.
The changes which are brought about by man are called man-made changes. These changes are under the control of man.
Example: Formation of curd, Burning of fuels, Cutting nails, Switching on an electric fan etc.
Examples of reversible changes are as follows:
- Melting of ice
- Pulling of rubber band
- Folding of paper
- Evaporation of water
Examples of non-reversible changes are as follows:
- Burning of a matchstick
- Germination of seed
- Rusting of iron
- Burning of fire crackers
Changes in which physical properties like shape, size and state change without formation of a new substance are called Physical changes.
Examples: Melting of wax, Boiling of water, Expansion of iron on heating etc.
The changes which take place in a long period of time are called slow changes.
- Baking a chapatti
- Burning of paper
- Burning of wood.
The changes which take place in a short period of time are called fast changes.
- Burning a matchstick
- Burning of magnesium ribbon
- Evaporation of petrol
Changes brought about by a person or the nature, which are harmful, are known as non-agreeable changes.
- Souring of milk
- Rusting of iron
- Spoiling of food
- Flooding of rivers
Changes which are desired to occur that is we want them to take place are known as desirable changes.
- Germination of seeds
- Growth of a child
- Healing of a wound
Periodic changes are as follows:
Day and night
Phases of the moon
Changes that do not repeat themselves at regular intervals of time are called non-periodic changes.
- Movement of spring: Reversible change
- Germination of a broad bean: Non-reversible change
- Growth of human being: Slow change
- Calcium oxide (Quick lime) reacts with water to form calcium hydroxide, also called slaked lime.
CaO + H2O → Ca(OH)2
A lot of heat is produced in the reaction. Due to this, sometimes water boils.
- When common salt is added to water, it forms a salt solution.
- Blowing of wind: Natural, Desirable, Non-periodic
- Ebb-tide: Natural, Periodic
- Formation of curd from milk: Non-reversible, Desirable
- Rainfall: Natural, Desirable
- Heating of wax: Physical, Reversible
- Pressing a rubber ball: Physical, Reversible
- Preparing organic manure: Man-made, Non-reversible
- Frying puris: Man-made, Non-reversible, Desirable
- Ripening of mangoes: Desirable, Non-reversible, Slow
- Contamination of food: Non-agreeable