Changes around us Notes
Answer the following questions:
1. Classify the following as slow or fast changes:
(i) ripening of fruits
(ii) curdling of milk by adding lemon juice
(iii) change of season
(iv) bursting of a cracker
(v) the spinning of a top
(vi) rusting of a bicycle rim
vii) the burning of paper
(viii) Weathering of a rock
1. Classify the following as slow or fast changes:
(i) ripening of fruits — slow change
(ii) curdling of milk by adding lemon juice— fast change
(iii) change of season — slow change
(iv) the bursting of a cracker — fast change
(v) the spinning of a top — fast change
(vi) rusting of a bicycle rim — slow change
(vii) the burning of paper — fast change
(viii) weathering of a rock — slow change
2. Give two examples each of:
(i) slow and fast changes
(ii) desirable and undesirable changes
(iii) periodic and non-periodic changes
(iv) reversible and irreversible changes
(v) physical and chemical changes
(i) the spinning of a top — fast change
the burning of paper — fast change
rusting of a bicycle rim — slow change
weathering of a rock — slow change
(ii) Desirable changes — formation of curd from milk formation of manure from cow-dung and dead plants.
Undesirable changes — spoiling of foodstuff, burning of a building
(iii) Periodic changes — the change of seasons the phases of the moon
Non-periodic changes — the growth of a plant, falling of leaves, rusting of an iron nail etc.
(iv) Reversible changes — The change from ice to water and water to ice and folding of leaves of touching me not plant.
Irreversible changes — Milk can be changed into curd but curd cannot be changed back into the milk. The growth of a child into an adult.
(v) Physical changes — Sublimation, Stretching of a rubber band.
Chemical changes — Burning of fuels, Rusting of iron.
3. State two changes which are desirable as well as undesirable.
Ans: (i) Change of seasons
(ii) Clothes getting worn out
4. What are periodic and non-periodic changes?
Ans: The changes that do not repeat themselves at regular intervals of time are known as non-periodic changes.
The changes that occur again and again after a fixed interval of time are known as periodic changes.
5. Classify the following changes as periodic or non-periodic:
(i) high and low tides in the sea
(ii) phases of the moon
(iii) the eruption of volcanoes
(iv) the falling of tree leaves
Ans: Classify the following changes as periodic or non-periodic:
(i) high and low tides in the sea — periodic change
(ii) phases of the moon — periodic change
(iii) the eruption of volcanoes — non-periodic change
(iv) the falling of tree leaves — non-periodic change
6. What are reversible and irreversible changes?
Ans: A change which can be reversed to the original form of a substance is called a reversible change. A change which cannot be reversed to form the original substance is known as an irreversible change.
7. Classify the following changes as reversible or irreversible:
(i) the breaking of a glass tumbler
(ii) cooking of rice
(iii) melting of Wax
iv) germination of seeds
(v) ploughing of a field
vi) stretching of a rubber band
(i) the breaking of a glass tumbler — irreversible change
(ii) cooking of rice — irreversible change
(iii) melting of wax — reversible change
(iv) germination of seeds — irreversible change
(v) ploughing of a field — irreversible change
(vi) stretching of a rubber band — reversible change
8. What are the physical and chemical changes?
A physical change is a temporary change in which the physical appearance of a substance may change but its chemical composition remains unchanged. A chemical change is a permanent change in which the composition of the substance changes giving rise to one or more new substances with different properties.
9. Classify the following cases as physical or chemical:
(i) cooking of food
(ii) curdling of milk
(iii) formation of clouds
(iv) the burning of a candle
(v) drying of wet hair
(vi) ironing of clothes
(vii) the souring of milk
(viii) rusting of iron
(ix) wool being knitted into a sweater
(x) coal burning in air
(i) cooking of food — chemical
(ii) curdling of milk — chemical
(iii) formation of clouds — physical change
(iv) the burning of a candle — physical change
(v) drying of wet hair — physical change
(vi) ironing of clothes — physical change
(vii) the souring of milk — a chemical change
(viii) rusting of iron — a chemical change
(ix) wool being knitted into a sweater — physical change
(x) coal burning in the air — a chemical change
Q- State whether the following statements are ‘True’ or ‘False’
(i) Curdling of milk is a desirable change.
(ii) Cooking of food is a physical change.
(iii) The occurrence of an earthquake is a periodic change.
(iv) The bursting of crackers is a fast as well as a chemical change.
(v) Dissolution of quicklime in water is an exothermic change.
(vi) The burning of paper is a reversible change.
(i) True, (ii) False, (iii) False, (iv) True, (v) True, (vi) False.
C. Pick the correct answer
(i) Which of the following is a chemical change?
(a) the breaking of a brick with a hammer
(b) melting of sulphur
(c) curdling of milk
(d) the beating of the heart
(ii) Which of the following is not a periodic change?
(a) The occurrence of day and night
(b) High and low tides in the sea
(c) Change of seasons
(iii) Ripening of fruits cannot be called as a/an
(a) slow change
(b) irreversible change
(c) desirable change
(d) physical change
(iv) Which of the following is a physical change?
(a) Burning of paper
(b) Formation of clouds
(c) Cooking of food
(d) Rusting of iron nails
(i) (c), (ii) (d), (iii) (d), (iv) (b)
CLASS VI SCIENCE