Sample Solution Paper 1 - Term- 1 Science, Class 8 Class 8 Notes | EduRev

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Class 8 : Sample Solution Paper 1 - Term- 1 Science, Class 8 Class 8 Notes | EduRev

 Page 1


  
 
CBSE VIII  |  SCIENCE 
Sample Paper – 1 Solution 
 
     
CBSE 
Class VIII Science 
Term 1 
Sample Paper – 1 Solution 
Time: 2 ½ hrs Total Marks: 80 
SECTION A 
 
1. Ans. Correct Option: [D] 
Solution: Dry soil requires watering before ploughing. After ploughing, the crumbs 
in the field have to be broken with a plank. Then the field is levelled for sowing as 
well as for irrigation purposes with the help of a leveller. 
 
2. Ans. Correct Option: [D] 
Solution: Viruses infect cells and take up the metabolic function of the host cell. 
Hence, it is difficult to kill only viruses without damaging the host cell. Hence, 
antibiotics are not effective against viruses and cannot cure diseases caused by a 
virus. 
 
3. Ans. Correct Option: [C] 
Solution: Citrus canker is an air-borne disease in plants, whereas measles is an air-
borne disease in humans. 
 
4. Ans. Correct Option: [B] 
Solution: Forests are natural habitats of animals. Due to deforestation, their natural 
habitat gets destroyed and such animals may fall prey to other animals and be killed. 
 
5. Ans. Correct Option: [B] 
Solution: Asiatic lion. This species has a wide distribution across southwest Asia. 
However, its population is now restricted only to India’s Gir forest. 
 
6. Ans. Correct Option: [B] 
Solution: Rayon is made of wood pulp. The wood obtained from plants is made of 
cellulose. 
 
7. Ans. Correct Option: [B] 
Solution: Thermoplastics get deformed easily on heating and can be bent easily. 
 
8. Ans. Correct Option: [B] 
Solution: Sodium is a metal which is soft and can be easily cut with a knife. 
  
Page 2


  
 
CBSE VIII  |  SCIENCE 
Sample Paper – 1 Solution 
 
     
CBSE 
Class VIII Science 
Term 1 
Sample Paper – 1 Solution 
Time: 2 ½ hrs Total Marks: 80 
SECTION A 
 
1. Ans. Correct Option: [D] 
Solution: Dry soil requires watering before ploughing. After ploughing, the crumbs 
in the field have to be broken with a plank. Then the field is levelled for sowing as 
well as for irrigation purposes with the help of a leveller. 
 
2. Ans. Correct Option: [D] 
Solution: Viruses infect cells and take up the metabolic function of the host cell. 
Hence, it is difficult to kill only viruses without damaging the host cell. Hence, 
antibiotics are not effective against viruses and cannot cure diseases caused by a 
virus. 
 
3. Ans. Correct Option: [C] 
Solution: Citrus canker is an air-borne disease in plants, whereas measles is an air-
borne disease in humans. 
 
4. Ans. Correct Option: [B] 
Solution: Forests are natural habitats of animals. Due to deforestation, their natural 
habitat gets destroyed and such animals may fall prey to other animals and be killed. 
 
5. Ans. Correct Option: [B] 
Solution: Asiatic lion. This species has a wide distribution across southwest Asia. 
However, its population is now restricted only to India’s Gir forest. 
 
6. Ans. Correct Option: [B] 
Solution: Rayon is made of wood pulp. The wood obtained from plants is made of 
cellulose. 
 
7. Ans. Correct Option: [B] 
Solution: Thermoplastics get deformed easily on heating and can be bent easily. 
 
8. Ans. Correct Option: [B] 
Solution: Sodium is a metal which is soft and can be easily cut with a knife. 
  
  
 
CBSE VIII  |  SCIENCE 
Sample Paper – 1 Solution 
 
     
9. Ans. Correct Option: [C] 
Solution: Iodine is a non-metal which is used as an antiseptic for skin treatment. 
 
10. Ans. Correct Option: [A] 
Solution: Metals combine with oxygen to form basic oxides. 
 
11. Ans. Correct Option: [B] 
Solution: The net force is 10 n - 5 n = 5 n (upwards). 
 
12. Ans. Correct Option: [A] 
Solution: Pulling a rope requires muscular force which is a contact force. Forces 
involved in all other cases may work from a distance. 
 
13. Ans. Correct Option: [D] 
Solution: Gym and tennis shoes have rubber soles rather than leather because 
rubber provides more friction than leather. 
 
14. Ans. Correct Option: [D] 
Solution: Timbre or quality of sound is a characteristic by virtue of which we can 
distinguish between two sounds of the same pitch and loudness. 
 
15. Ans. Correct Option: [B] 
Solution: Sounds with frequencies lower than 20 Hz are below audible level and 
hence are called infrasonic sound. 
 
SECTION B 
 
16. Ans.  
 
Kharif Crops Rabi Crops 
i. Crops grown in the monsoon and 
harvested in autumn are called 
kharif crops. 
i. Crops grown in the 
winter season are called 
rabi crops. 
ii. Their time period is the rainy 
season in India which is generally 
from June to September. 
ii. Their time period is 
generally from October 
to March. 
iii. Examples: Rice, maize, tobacco, 
potato, onion, soyabean, millets  
iii. Examples: Wheat, 
mustard, pea, barley, 
gram  
 
Page 3


  
 
CBSE VIII  |  SCIENCE 
Sample Paper – 1 Solution 
 
     
CBSE 
Class VIII Science 
Term 1 
Sample Paper – 1 Solution 
Time: 2 ½ hrs Total Marks: 80 
SECTION A 
 
1. Ans. Correct Option: [D] 
Solution: Dry soil requires watering before ploughing. After ploughing, the crumbs 
in the field have to be broken with a plank. Then the field is levelled for sowing as 
well as for irrigation purposes with the help of a leveller. 
 
2. Ans. Correct Option: [D] 
Solution: Viruses infect cells and take up the metabolic function of the host cell. 
Hence, it is difficult to kill only viruses without damaging the host cell. Hence, 
antibiotics are not effective against viruses and cannot cure diseases caused by a 
virus. 
 
3. Ans. Correct Option: [C] 
Solution: Citrus canker is an air-borne disease in plants, whereas measles is an air-
borne disease in humans. 
 
4. Ans. Correct Option: [B] 
Solution: Forests are natural habitats of animals. Due to deforestation, their natural 
habitat gets destroyed and such animals may fall prey to other animals and be killed. 
 
5. Ans. Correct Option: [B] 
Solution: Asiatic lion. This species has a wide distribution across southwest Asia. 
However, its population is now restricted only to India’s Gir forest. 
 
6. Ans. Correct Option: [B] 
Solution: Rayon is made of wood pulp. The wood obtained from plants is made of 
cellulose. 
 
7. Ans. Correct Option: [B] 
Solution: Thermoplastics get deformed easily on heating and can be bent easily. 
 
8. Ans. Correct Option: [B] 
Solution: Sodium is a metal which is soft and can be easily cut with a knife. 
  
  
 
CBSE VIII  |  SCIENCE 
Sample Paper – 1 Solution 
 
     
9. Ans. Correct Option: [C] 
Solution: Iodine is a non-metal which is used as an antiseptic for skin treatment. 
 
10. Ans. Correct Option: [A] 
Solution: Metals combine with oxygen to form basic oxides. 
 
11. Ans. Correct Option: [B] 
Solution: The net force is 10 n - 5 n = 5 n (upwards). 
 
12. Ans. Correct Option: [A] 
Solution: Pulling a rope requires muscular force which is a contact force. Forces 
involved in all other cases may work from a distance. 
 
13. Ans. Correct Option: [D] 
Solution: Gym and tennis shoes have rubber soles rather than leather because 
rubber provides more friction than leather. 
 
14. Ans. Correct Option: [D] 
Solution: Timbre or quality of sound is a characteristic by virtue of which we can 
distinguish between two sounds of the same pitch and loudness. 
 
15. Ans. Correct Option: [B] 
Solution: Sounds with frequencies lower than 20 Hz are below audible level and 
hence are called infrasonic sound. 
 
SECTION B 
 
16. Ans.  
 
Kharif Crops Rabi Crops 
i. Crops grown in the monsoon and 
harvested in autumn are called 
kharif crops. 
i. Crops grown in the 
winter season are called 
rabi crops. 
ii. Their time period is the rainy 
season in India which is generally 
from June to September. 
ii. Their time period is 
generally from October 
to March. 
iii. Examples: Rice, maize, tobacco, 
potato, onion, soyabean, millets  
iii. Examples: Wheat, 
mustard, pea, barley, 
gram  
 
  
 
CBSE VIII  |  SCIENCE 
Sample Paper – 1 Solution 
 
     
17. Ans. Modern methods of irrigation help us to use water economically, i.e. it prevents 
wastage of water. These methods also help to save time and labour. Hence, they are 
more efficient than traditional methods of irrigation. 
 
18. Ans. Uses of microorganisms in agriculture: Microorganisms help in manure 
formation and in increasing soil fertility. 
Uses of microorganisms in medicine: Microorganisms are used to prepare 
antibiotics and vaccines. 
 
19. Ans. Plastics are replacing metals in the car industry because  
(i) They are cheaper than metals. 
(ii) They can be easily moulded in various shapes. 
 
20. Ans. Yes. We can classify substances as metals and non-metals based on lustre. 
Metals have a shiny lustre, while non-metals generally do not have a shiny lustre. 
 
21. Ans.  
(i) Cricket ball hit by a batsman: Push 
(ii) Planting a pin on the pin board: Push 
(iii) Plucking the nail off the wall: Pull 
(iv) Picking up a shopping bag: Pull 
 
22. Ans. Friction is because of irregularities of two surfaces in contact. In sliding 
friction, the time given for the interlocking of the irregularities of the two surfaces is  
small, and that is why sliding friction is less than static friction. 
 
 
SECTION C 
23. Ans.  
(i) Significance of a biosphere reserve is as follows: 
1. To provide opportunities to conduct studies on different plants and animals. 
2. To protect the tribal people living in the area. 
3. To maintain the ecological balance of the area. 
 
(ii) Carbon dioxide is known as a greenhouse gas. Plants absorb atmospheric carbon 
dioxide to carry out the process of photosynthesis. Deforestation, human 
activities and pollution have lead to the increase in the concentration of carbon 
dioxide. CO 2 traps the heat rays reflected by the Earth which leads to an increase 
in the average temperature of the Earth and causes global warming. 
 
  
Page 4


  
 
CBSE VIII  |  SCIENCE 
Sample Paper – 1 Solution 
 
     
CBSE 
Class VIII Science 
Term 1 
Sample Paper – 1 Solution 
Time: 2 ½ hrs Total Marks: 80 
SECTION A 
 
1. Ans. Correct Option: [D] 
Solution: Dry soil requires watering before ploughing. After ploughing, the crumbs 
in the field have to be broken with a plank. Then the field is levelled for sowing as 
well as for irrigation purposes with the help of a leveller. 
 
2. Ans. Correct Option: [D] 
Solution: Viruses infect cells and take up the metabolic function of the host cell. 
Hence, it is difficult to kill only viruses without damaging the host cell. Hence, 
antibiotics are not effective against viruses and cannot cure diseases caused by a 
virus. 
 
3. Ans. Correct Option: [C] 
Solution: Citrus canker is an air-borne disease in plants, whereas measles is an air-
borne disease in humans. 
 
4. Ans. Correct Option: [B] 
Solution: Forests are natural habitats of animals. Due to deforestation, their natural 
habitat gets destroyed and such animals may fall prey to other animals and be killed. 
 
5. Ans. Correct Option: [B] 
Solution: Asiatic lion. This species has a wide distribution across southwest Asia. 
However, its population is now restricted only to India’s Gir forest. 
 
6. Ans. Correct Option: [B] 
Solution: Rayon is made of wood pulp. The wood obtained from plants is made of 
cellulose. 
 
7. Ans. Correct Option: [B] 
Solution: Thermoplastics get deformed easily on heating and can be bent easily. 
 
8. Ans. Correct Option: [B] 
Solution: Sodium is a metal which is soft and can be easily cut with a knife. 
  
  
 
CBSE VIII  |  SCIENCE 
Sample Paper – 1 Solution 
 
     
9. Ans. Correct Option: [C] 
Solution: Iodine is a non-metal which is used as an antiseptic for skin treatment. 
 
10. Ans. Correct Option: [A] 
Solution: Metals combine with oxygen to form basic oxides. 
 
11. Ans. Correct Option: [B] 
Solution: The net force is 10 n - 5 n = 5 n (upwards). 
 
12. Ans. Correct Option: [A] 
Solution: Pulling a rope requires muscular force which is a contact force. Forces 
involved in all other cases may work from a distance. 
 
13. Ans. Correct Option: [D] 
Solution: Gym and tennis shoes have rubber soles rather than leather because 
rubber provides more friction than leather. 
 
14. Ans. Correct Option: [D] 
Solution: Timbre or quality of sound is a characteristic by virtue of which we can 
distinguish between two sounds of the same pitch and loudness. 
 
15. Ans. Correct Option: [B] 
Solution: Sounds with frequencies lower than 20 Hz are below audible level and 
hence are called infrasonic sound. 
 
SECTION B 
 
16. Ans.  
 
Kharif Crops Rabi Crops 
i. Crops grown in the monsoon and 
harvested in autumn are called 
kharif crops. 
i. Crops grown in the 
winter season are called 
rabi crops. 
ii. Their time period is the rainy 
season in India which is generally 
from June to September. 
ii. Their time period is 
generally from October 
to March. 
iii. Examples: Rice, maize, tobacco, 
potato, onion, soyabean, millets  
iii. Examples: Wheat, 
mustard, pea, barley, 
gram  
 
  
 
CBSE VIII  |  SCIENCE 
Sample Paper – 1 Solution 
 
     
17. Ans. Modern methods of irrigation help us to use water economically, i.e. it prevents 
wastage of water. These methods also help to save time and labour. Hence, they are 
more efficient than traditional methods of irrigation. 
 
18. Ans. Uses of microorganisms in agriculture: Microorganisms help in manure 
formation and in increasing soil fertility. 
Uses of microorganisms in medicine: Microorganisms are used to prepare 
antibiotics and vaccines. 
 
19. Ans. Plastics are replacing metals in the car industry because  
(i) They are cheaper than metals. 
(ii) They can be easily moulded in various shapes. 
 
20. Ans. Yes. We can classify substances as metals and non-metals based on lustre. 
Metals have a shiny lustre, while non-metals generally do not have a shiny lustre. 
 
21. Ans.  
(i) Cricket ball hit by a batsman: Push 
(ii) Planting a pin on the pin board: Push 
(iii) Plucking the nail off the wall: Pull 
(iv) Picking up a shopping bag: Pull 
 
22. Ans. Friction is because of irregularities of two surfaces in contact. In sliding 
friction, the time given for the interlocking of the irregularities of the two surfaces is  
small, and that is why sliding friction is less than static friction. 
 
 
SECTION C 
23. Ans.  
(i) Significance of a biosphere reserve is as follows: 
1. To provide opportunities to conduct studies on different plants and animals. 
2. To protect the tribal people living in the area. 
3. To maintain the ecological balance of the area. 
 
(ii) Carbon dioxide is known as a greenhouse gas. Plants absorb atmospheric carbon 
dioxide to carry out the process of photosynthesis. Deforestation, human 
activities and pollution have lead to the increase in the concentration of carbon 
dioxide. CO 2 traps the heat rays reflected by the Earth which leads to an increase 
in the average temperature of the Earth and causes global warming. 
 
  
  
 
CBSE VIII  |  SCIENCE 
Sample Paper – 1 Solution 
 
     
24. Ans. 
(i) A farmer needs to carry out the following steps in order to ensure the safe 
storage of the harvest: 
1. The fresh crop should be properly dried in the Sun to reduce the moisture in 
them so as to prevent the attack by moulds and fungi. 
2. The grains should be stored in jute bags or metallic bins to protect them from 
pests. 
3. Specific chemical treatments must be carried out for storing large quantities 
of grains in big godowns to protect them from pests and microorganisms. 
(ii) Lowering of temperature slows down the growth of bacteria, yeast and moulds, 
and inhibits the action of enzymes present in the food material and helps to 
increase the shelf-life of food. 
 
25. Ans.  
(i) Three methods of food preservation are as follows: 
1. Preservation by common salt: Meat and fish are preserved by covering with 
dry salt. Salting prevents the growth of bacteria. Salting is also used in the 
preservation of amla, pickles, tamarind etc. 
2. Preservation by oil and vinegar: Vinegar too prevents the growth of bacteria. 
Hence, it is used in pickles, vegetables, fruits and fish. 
3. Heat and cold treatments: Some bacteria cannot thrive at high temperature 
and at  low temperatures. Hence, certain food items (e.g. milk) are boiled, and 
food is stored in the refrigerator. 
(ii) Sodium benzoate and sodium metabisulphite are two common preservatives.  
 
26. Ans. A material which gets decomposed through natural processes (such as the 
action of bacteria) is called a biodegradable material. 
Examples: Peels of vegetables and fruits, wood  
A material which is not easily decomposed by natural processes (such as the action 
of bacteria) is called non-biodegradable material. 
Examples: Plastics, glass  
 
  
Page 5


  
 
CBSE VIII  |  SCIENCE 
Sample Paper – 1 Solution 
 
     
CBSE 
Class VIII Science 
Term 1 
Sample Paper – 1 Solution 
Time: 2 ½ hrs Total Marks: 80 
SECTION A 
 
1. Ans. Correct Option: [D] 
Solution: Dry soil requires watering before ploughing. After ploughing, the crumbs 
in the field have to be broken with a plank. Then the field is levelled for sowing as 
well as for irrigation purposes with the help of a leveller. 
 
2. Ans. Correct Option: [D] 
Solution: Viruses infect cells and take up the metabolic function of the host cell. 
Hence, it is difficult to kill only viruses without damaging the host cell. Hence, 
antibiotics are not effective against viruses and cannot cure diseases caused by a 
virus. 
 
3. Ans. Correct Option: [C] 
Solution: Citrus canker is an air-borne disease in plants, whereas measles is an air-
borne disease in humans. 
 
4. Ans. Correct Option: [B] 
Solution: Forests are natural habitats of animals. Due to deforestation, their natural 
habitat gets destroyed and such animals may fall prey to other animals and be killed. 
 
5. Ans. Correct Option: [B] 
Solution: Asiatic lion. This species has a wide distribution across southwest Asia. 
However, its population is now restricted only to India’s Gir forest. 
 
6. Ans. Correct Option: [B] 
Solution: Rayon is made of wood pulp. The wood obtained from plants is made of 
cellulose. 
 
7. Ans. Correct Option: [B] 
Solution: Thermoplastics get deformed easily on heating and can be bent easily. 
 
8. Ans. Correct Option: [B] 
Solution: Sodium is a metal which is soft and can be easily cut with a knife. 
  
  
 
CBSE VIII  |  SCIENCE 
Sample Paper – 1 Solution 
 
     
9. Ans. Correct Option: [C] 
Solution: Iodine is a non-metal which is used as an antiseptic for skin treatment. 
 
10. Ans. Correct Option: [A] 
Solution: Metals combine with oxygen to form basic oxides. 
 
11. Ans. Correct Option: [B] 
Solution: The net force is 10 n - 5 n = 5 n (upwards). 
 
12. Ans. Correct Option: [A] 
Solution: Pulling a rope requires muscular force which is a contact force. Forces 
involved in all other cases may work from a distance. 
 
13. Ans. Correct Option: [D] 
Solution: Gym and tennis shoes have rubber soles rather than leather because 
rubber provides more friction than leather. 
 
14. Ans. Correct Option: [D] 
Solution: Timbre or quality of sound is a characteristic by virtue of which we can 
distinguish between two sounds of the same pitch and loudness. 
 
15. Ans. Correct Option: [B] 
Solution: Sounds with frequencies lower than 20 Hz are below audible level and 
hence are called infrasonic sound. 
 
SECTION B 
 
16. Ans.  
 
Kharif Crops Rabi Crops 
i. Crops grown in the monsoon and 
harvested in autumn are called 
kharif crops. 
i. Crops grown in the 
winter season are called 
rabi crops. 
ii. Their time period is the rainy 
season in India which is generally 
from June to September. 
ii. Their time period is 
generally from October 
to March. 
iii. Examples: Rice, maize, tobacco, 
potato, onion, soyabean, millets  
iii. Examples: Wheat, 
mustard, pea, barley, 
gram  
 
  
 
CBSE VIII  |  SCIENCE 
Sample Paper – 1 Solution 
 
     
17. Ans. Modern methods of irrigation help us to use water economically, i.e. it prevents 
wastage of water. These methods also help to save time and labour. Hence, they are 
more efficient than traditional methods of irrigation. 
 
18. Ans. Uses of microorganisms in agriculture: Microorganisms help in manure 
formation and in increasing soil fertility. 
Uses of microorganisms in medicine: Microorganisms are used to prepare 
antibiotics and vaccines. 
 
19. Ans. Plastics are replacing metals in the car industry because  
(i) They are cheaper than metals. 
(ii) They can be easily moulded in various shapes. 
 
20. Ans. Yes. We can classify substances as metals and non-metals based on lustre. 
Metals have a shiny lustre, while non-metals generally do not have a shiny lustre. 
 
21. Ans.  
(i) Cricket ball hit by a batsman: Push 
(ii) Planting a pin on the pin board: Push 
(iii) Plucking the nail off the wall: Pull 
(iv) Picking up a shopping bag: Pull 
 
22. Ans. Friction is because of irregularities of two surfaces in contact. In sliding 
friction, the time given for the interlocking of the irregularities of the two surfaces is  
small, and that is why sliding friction is less than static friction. 
 
 
SECTION C 
23. Ans.  
(i) Significance of a biosphere reserve is as follows: 
1. To provide opportunities to conduct studies on different plants and animals. 
2. To protect the tribal people living in the area. 
3. To maintain the ecological balance of the area. 
 
(ii) Carbon dioxide is known as a greenhouse gas. Plants absorb atmospheric carbon 
dioxide to carry out the process of photosynthesis. Deforestation, human 
activities and pollution have lead to the increase in the concentration of carbon 
dioxide. CO 2 traps the heat rays reflected by the Earth which leads to an increase 
in the average temperature of the Earth and causes global warming. 
 
  
  
 
CBSE VIII  |  SCIENCE 
Sample Paper – 1 Solution 
 
     
24. Ans. 
(i) A farmer needs to carry out the following steps in order to ensure the safe 
storage of the harvest: 
1. The fresh crop should be properly dried in the Sun to reduce the moisture in 
them so as to prevent the attack by moulds and fungi. 
2. The grains should be stored in jute bags or metallic bins to protect them from 
pests. 
3. Specific chemical treatments must be carried out for storing large quantities 
of grains in big godowns to protect them from pests and microorganisms. 
(ii) Lowering of temperature slows down the growth of bacteria, yeast and moulds, 
and inhibits the action of enzymes present in the food material and helps to 
increase the shelf-life of food. 
 
25. Ans.  
(i) Three methods of food preservation are as follows: 
1. Preservation by common salt: Meat and fish are preserved by covering with 
dry salt. Salting prevents the growth of bacteria. Salting is also used in the 
preservation of amla, pickles, tamarind etc. 
2. Preservation by oil and vinegar: Vinegar too prevents the growth of bacteria. 
Hence, it is used in pickles, vegetables, fruits and fish. 
3. Heat and cold treatments: Some bacteria cannot thrive at high temperature 
and at  low temperatures. Hence, certain food items (e.g. milk) are boiled, and 
food is stored in the refrigerator. 
(ii) Sodium benzoate and sodium metabisulphite are two common preservatives.  
 
26. Ans. A material which gets decomposed through natural processes (such as the 
action of bacteria) is called a biodegradable material. 
Examples: Peels of vegetables and fruits, wood  
A material which is not easily decomposed by natural processes (such as the action 
of bacteria) is called non-biodegradable material. 
Examples: Plastics, glass  
 
  
  
 
CBSE VIII  |  SCIENCE 
Sample Paper – 1 Solution 
 
     
27. Ans.  
(i) Coal is a hard, black combustible mineral which consists mainly of carbon. 
(ii) Coal is a source of energy:  
Coal is mainly carbon. When heated in air, coal burns and produces mainly 
carbon dioxide gas. A lot of heat energy is also produced during the burning of 
coal. This can be written as 
 
Coal is important because it can be used as a source of heat energy (just by 
burning it), or it can be converted into other forms of energy such as coal gas, 
coke or electricity. 
(iii) The real source of energy of coal is solar energy (or the Sun's energy). This is 
because the plants and trees which decomposed to form coal grew on the Earth 
by absorbing sunlight energy during the process of photosynthesis. 
 
28. Ans.  
(i) Balanced Forces: When the resultant of all the forces acting on a body is zero, the 
forces are said to be balanced forces. 
Unbalanced Forces: When the resultant of all the forces acting on a body is not 
zero, the forces are unbalanced forces. 
(ii) The materials which break easily when force is applied on them are considered 
brittle. Examples of brittle materials are ceramic and glass. Objects made of 
plastic and wood are non-brittle in nature. 
 
29. Ans.  
(i) When oil is applied between the two surfaces in contact, a thin layer of oil is 
formed between the two surfaces. This layer separates the two surfaces a little 
bit due to which their interlocking is reduced to a large extent when they rub 
against each other.  
 
(ii) Grease and oil are two commonly used lubricants. 
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