Class 8 Science

CBSE Class 8 Science Chapter 4 Combustion And Flame Review Exercise Multiple Choice Questions

Question 1. Combustion is a process that

1. Releases Light And Heat
2. Absorbs Light And Heat
3. Produces Only Heat
4. Produces Only Light

Answer: 1. Releases Light And Heat

Question 2. Combustion is generally

1. A Physical Process
2. A Chemical Process
3. Both 1 And 2
4. None Of These

Answer: 2. A Chemical Process

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Question 3. The product(s) of combustion is or are

1. Only Oxygen
2. Oxygen And Water
3. Carbon Dioxide And Water
4. Only Carbon Dioxide

Answer: 3. Carbon Dioxide And Water

Question 4. Magnesium ribbon, on burning in air, produces

1. Magnesium Oxide, Water, And Light
2. Magnesium Oxide And Heat
3. Magnesium Oxide, Heat, And Light
4. Magnesium Oxide, Water, And Heat

Answer: 3. Magnesium Oxide, Heat, And Light

Question 5. Coal burns with

1. Flame
2. Only Glow
3. Both Flame And Glow
4. None Of These

Answer: 2. Only Glow

Question 6. The substance that does not burn with flame is

1. LPG
2. Camphor
3. Dry Grass
4. Charcoal

Answer: 4. Charcoal

Question 7. Which of these materials is combustible?

1. Steel
2. Wood
3. Glass
4. Marble

Answer: 2. Wood

Question 8. Which of the following is not a combustible substance?

1. Camphor
2. Glass
3. Straw
4. Alcohol

Answer: 2. Glass

Question 9. A substance that reacts with oxygen, giving heat, is called a combustible substance. Which one of the following is a combustible substance?

1. Iron nail
2. Glass
3. Stone piece
4. Wood

Answer: 4. Wood

Question 10. If a person’s clothes catch fire, the best way to extinguish the fire is to

1. Throw water on the clothes
2. Use a fire extinguisher
3. Cover the person with a woolen blanket
4. Cover the person with a polythene sheet

Answer: 3. Cover the person with a woolen blanket

Question 11. The substance expected to have the highest Ignition temperature out of the following is

1. Kerosene
2. Petrol
3. Coal
4. Alcohol

Answer: 3. Coal

Class 8 Science Chapter 4 Combustion And Flame

Question 12. Water was poured over a large oil fire to extinguish it. What would happen and why?

1. The fire will be put off since water extinguishes fires
2. The fire will spread since oil floats on water
3. The fire will be put off since water dissolves oil
4. The fire will spread since water contains hydrogen, which is a combustible gas

Answer: 2. The fire will spread since oil floats on water

Question 13. In a fire extinguisher, which substance is commonly used for cutting off the oxygen supply to the fire?

1. Water
2. Sand
3. Carbon dioxide
4. Gasoline

Answer: 3. Carbon dioxide

Question 14. On placing an inverted tumbler over a burning candle, the flame extinguishes after some time. This is because of the non-availability of

1. Oxygen
2. Water vapour
3. Carbon dioxide
4. Wax

Answer: 1. Carbon dioxide

Question 15. When a lighted candle placed partly in a trough of water is covered by an inverted glass, water rushes up as shown, and the flame extinguishes. If the above hypothesis is true, what will happen after the candle blows out in the new experimental setup?

1. The mouse will die or show signs of suffocation
2. The mouse will become more active
3. The glass will break, and the mouse will escape
4. There will be no change in the mouse’s behaviour

Answer: 1. The mouse will die or show signs of suffocation

CBSE Class 8 Science Chapter 9 Friction Very Short Answer Questions

Question 1. Will the force of friction come into play when a raindrop rolls down a glass window pane?
Answer: Yes, friction comes into play when two surfaces are in contact, but in a very small amount.

Question 2. If a body is moving on a rough horizontal surface towards the east, then in which direction will the frictional force act?
Answer: Frictional force always acts in the direction opposite to the direction of motion, so it will act towards the west.

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Question 3. The figure shows two boys applying force to a box. If the magnitude of the force applied by each is equal, will the box experience any force of friction?

Answer: No, the force applied by both boys is equal. So, the net force will be zero, and hence friction force will not come into play.

Question 4. It is easier to drag a carpet from the floor, but it is difficult to drag the carpet when someone is sitting on it. Explain the reason behind it.
Answer: If the two surfaces are pressed harder, then the force of friction will increase. So, it is easy to drag a carpet when nobody is sitting on it, but when a person is sitting on it, then it produces more friction.

Question 5. Why does a matchstick catch fire when it is rubbed on a rough surface?
Answer: On rubbing the matchstick on a rough surface, the temperature increases due to friction, making the matchstick catch fire.

Question 6. The jar of a mixer becomes hot when it is run for a few minutes. Comment.
Answer: Due to friction, the jar of a mixer becomes hot when it is run for a few minutes.

Question 7. Give n reason for railing friction as n necessary evil.
Answer: Friction is a necessary evil because it causes a lot of wear and tear.

Question 8. Why do kabaddi players rub their hands with soil?
Answer: Kabaddi players rub their hands with soil to increase the friction, so that they can grip the opposing team players firmly.

Question 9. Why do weightlifters apply chalk powder on their palms while lifting weights?
Answer: It increases the roughness in their hand. This provides a better grip while lifting weights.

Question 10. Why are oil, creams, and grease called lubricants?
Answer: Oil, creams and grease, when applied on a surface, make it smooth, thus reducing friction, so these are called lubricants.

Question 11. Can we eliminate friction?
Answer: No, we cannot eliminate friction because it is a characteristic property (molecular property) of a material.

Question 12. What is the special shape of the objects moving in fluids?
Answer: Streamlined shape is the special shape given to objects moving in fluids.

Question 13. Explain fluid friction brief.
Answer: When an object moves in a fluid, the resistance to the movement of the object exerted by the fluid is called fluid friction.

Question 14. Why does an arrow with a pointed tip move faster in the air than one with a flat tip?
Answer: The arrow with a pointed tip suffers small air resistance due to its pointed shape, so it moves faster.

CBSE Class 8 Science Chapter 4 Combustion And Flame Long Answer Questions

Question 1. In an experiment, 4.5 kg of a fuel was completely burnt. The heat produced was measured to be 180000 kJ. Calculate the calorific value of the fuel.
Answer: The amount of heat energy produced on the complete combustion of 1 kg of a fuel is called its calorific value.

Given, total mass of fuel = 4.5 kg

Total heat produced = 180000 kJ

Now, the heat produced in burning 1 kg of fuel, i.e., calorific value

⇒ \(\begin{aligned}
& =\frac{\text { Total heat produced }}{\text { Total mass of fuel }}=\frac{180000}{4.5} \\
& =\frac{180000 \times 10}{45}=\frac{1800000}{45} \\
& =\frac{360000}{9}=40000 \mathrm{~kJ} / \mathrm{kg} \quad \text { (divid }
\end{aligned}\)

Hence, calorific value of fuel =40000 kJ/kg

Question 2. Can the process of rusting be called combustion? Discuss.
Answer: The process of rusting cannot be called combustion because, in this process, no heat and light are produced. For this reason, iron is not considered a combustible substance.

Question 3. Abida and Ramesh were doing an experiment in which water was to be heated in a beaker. Abida kept the beaker near the wick in the yellow part of the candle flame. Ramesh kept the beaker in the outermost part of the flame. Whose water will get heated in a shorter time?
Answer: The water heated by Ramesh will get heated in a shorter time because he kept his beaker near the hottest (non-luminous) zone of the flame. 

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Question 4. Sparkling rods light up when inserted into a flame. The hotter the flame, the quicker the rod lights up. Tito’s picture shows four different zones of a flame.

1. In which zone should a sparkling rod be inserted to light it the fastest?

1. Zone 1
2. Zone 2
3. Zone 3
4. Zone 4

Answer: 1. Zone 1

2. Why does the flame of a candle go off when all the wax melts?

Answer: The flame of the candle goes off because no more wax is available on the candle, which can burn and give flame.

Which zone has unburnt carbon particles?

1. Zone 1
2. Zone 2
3. Zone 3
4. Zone 4

Answer: 3. Zone 3

Question 5. Observe the given picture and answer the following questions

1. Which is the hottest part of the flame in the given figure of a candle?
Answer: A or the outermost part of the flame.

2. Why does the middle zone of the candle flame glow with yellow colour?
Answer: The Middle zone of the candle flame contains unburnt carbon particles, which give the flame a yellow colour.

3. State any two conditions under which combustion takes place.
Answer: The Presence of a supporter of combustion and the presence of a combustible substance are two required conditions for combustion.

Question 6.

(1) In an experiment, 6.5 kg of a fuel was completely burnt. The heat produced was measured to be 1,90,000 KJ. Calculate the calorific value of the fuel in KJ per kg.

Answer: \(\begin{aligned}
& \text { Calorific value }=\text { Energy } / \text { Mass } \\
& =\frac{190000}{65}=29230 \mathrm{~kJ} / \mathrm{kg}
\end{aligned}\)

(2) CNG is a better fuel when compared to petrol or diesel. Regarding the data in the table, evaluate this statement

Answer: CNG produces less carbon monoxide than diesel and produces less greenhouse gas than diesel. Also, CNG has a higher energy density than diesel.

Question 7. The picture shows four types of fire extinguishers. Each extinguisher is suited for specific sources of fire.

1. A tailor has money for any two of the fire extinguishers. Which pair of fire extinguishers should be bought for his tailoring shop?

1. P and Q
2. Q and S
3. P and R
4. S and R

Answer: 3. P and R

2. Fire extinguisher K is suitable for kitchen fires.

1. Which fire extinguisher can perform most of the work of K?

1. P
2. Q
3. R
4. S

Answer: 2. Q

2. How does dumping sand on a fire extinguish the flame?

Answer: Sand absorbs heat and cuts off the oxygen supply, hence, it helps in extinguishing the flame.

Question 9. Although wood has a very high calorific value, we still discourage its use as a fuel. Explain.
Answer: Burning of wood has several disadvantages despite having a high calorific value. These are as follows-

Burning wood produces a lot of smoke, which causes respiratory diseases like asthma.

The cutting down of trees to obtain as a wood fuel leads to deforestation which is very harmful to the environment.

Trees provide us many useful substances. To obtain fuel wood, when trees are cut down, then all useful substances which can be obtained from trees are lost.

Question 10. A forest fire produces a lot of air pollution. Write a brief about the reasons for forest fires.
The reasons for forest fires are as follows

• At high temperatures, sometimes dry grass catches fire, which spreads throughout the forest.
• A campfire may also be a reason for fire.
• Lightning.
• The use of fires by villagers to ward off wild animals.
• Fire was lit intentionally by people living around forests for recreation.
• The friction of bamboo due to high wind velocity and rolling stones.

Question 11. Manu was heating oil to fry potato chips. The cooking oil all of a sudden caught fire, he poured water to extinguish the fire. Do you think, this action was suitable? If yes, why? If not, why not? In such a condition what should Manu have done?
Answer: Pouring water to extinguish the fire due to oil is not a suitable action. It is because oil is lighter than water. So, water will settle down below the oil. In such a condition, sand or soil should be used.

They cut off the supply of air to the fire. Thus, fire can be controlled. But sand or soil will not be available at that place.

So, Manu should have switched off the flame ofthe burner and put a lid on the frying pan. By doing this, the contact between fuel and oxygen is cut, and the flame could go off.

Simple Friction Experiments For Class 8 CBSE Students Activity 1

Aim: To observe the opposing or friction force.

Material Required: A table, a book

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Procedure:

1. Firstly, take a book and place it on the table.
2. Now, push the book gently towards the right. You will find that the book stops after covering some distance.
3. Now, push the book towards the left, and you will find that the book stops after covering some distance.

Conclusion: We can see that when the force is acting towards the left, the friction is towards the right, and when the force is acting towards the right, the friction is towards the left. Hence, we conclude that the force of friction always acts in a direction opposite to the direction of motion of an object

Fun Hands-On Friction Experiments For Grade 8 Students Activity 2

Aim: To show that the magnitude of friction is less over smooth surfaces with the help ofspring balance.

Material Required: A brick, a spring balance.

Procedure:

1. Firstly, tie a string around a brick and connect it to the hook of the spring balance.
2. Fully extend the other end of the spring balance by hand till the brick just begins to move.
3. Note the reading on the spring balance. It will give you the magnitude of the force of friction between the surface of the brick and the floor.
4. Now, wrap a piece of polythene around the brick and repeat the above steps to measure the magnitude ot the friction force.

Conclusion: We have concluded that the magnitude of friction is less, when we wrap the brick with a polythene. It means that smooth surfaces produce less friction.

Rolling Friction Demonstration ActivityFor Class 8 Science Activity 3

Aim: To observe the dependence of friction on the nature of surfaces.

Material Required: Wooden board, a pencil cell, a piece of cloth, some books, a table.

Procedure:

Firstly, set up an inclined plane on a smooth table by placing a wooden board supported by some books as shown.

Put a mark A on the inclined plane and let a pencil cell move down from this mark. Note the distance covered by the pencil cell on the table.

Now, put a piece of cloth over the table. Repeat the above steps again on the cloth spread over table. You will find that distance covered by the pencil cell is less than the distance covered in first case.

Again, repeat this activity by spreading a thin layer of sand over the table. You will find that the distance covered by the pencil cell is very small.

Conclusion: We have concluded that the distance covered by the pencil cell is different on different surfaces. Thus, the friction depends on the nature of the two surfaces in contact.

Class 8 Friction Activity Worksheet With Observations Activity 4

Aim: To show that rolling friction is less than the friction.

Material Required: A book. few pencils.

Procedure:

1. Firstly, take a few pencils of cylindrical shape and place them parallel to each other on a table.
2. Place a thick book over it.
3. Now, push the book gently. You will find that the pencils roll as the book moves.

Here, we find it easier to move the book in this way than to slide it.

Conclusion: We have concluded that the friction can be reduced by attaching wheels, to move an object. It is always easier to move an object by rolling as compare to sliding it.

CBSE Class 8 Science Chapter 9 Friction Fill In The Blanks

Question 1. Friction opposes the _________ between the surfaces in contact with each other.
Answer: Relative motion

Question 2. Friction depends on the _________ of surfaces.
Answer: Nature

Question 3. Friction produces _________.
Answer: Heat

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Question 4. Sprinkling of powder on the carrom board _________ friction.
Answer: Reduces

Question 5. Sliding friction is _________ than the static friction.
Answer: Less

Question 6. A spring balance is a device used for measuring the ________ acting on the object.
Answer: force

Question 7. On smooth surfaces, there are ________ number of irregularities. While on rough surfaces, there are an _______ number of irregularities.
Answer: Less, Large

Question 8. Friction can never be entirely ________.
Answer: Eliminated

Question 9. The soles of our shoes get worn out after a period of time. It is due to ________.
Answer: Friction

Question 10. ________ is produced by friction.
Answer: Heat

Question 11. Ball bearings reduce friction because they roll rather than ________.
Answer: Slide

Question 12. We pour a drop of oil on the hinge of the door to ________ friction.
Answer: Reduce

Question 13. Cars and speedboats are ________ to reduce drag.
Answer: Streamlined

Class 8 Science Chapter 9 Friction True Or False

Question 1. A fraction always works in the direction of the motion of the body.
Answer: False

Question 2. A soapy floor is slippery due to less friction.
Answer: True

Question 3. Friction increases with an increase in the smoothness of the surface.
Answer: False

Question 4. It is easier to roll the body over one another than to slide it.
Answer: True

Question 5. Friction enables vehicles to move on the ground.
Answer: True

Question 6. Fluid friction depends on the shape of an object placed in the fluid and the nature of the fluid.
Answer: True

Question 7. Athletes wear spikes to increase muscular force.
Answer: False

Question 8. A streamlined body shape helps in reducing drag.
Answer: True

Question 9. Frictional force does not depend on the nature of the
surfaces in contact
Answer: False

Class 8 Science Chapter 9 Friction Match The Columns

Question 1. Match Column 1 with those In Column 2

Answer: (a)-(2), (b)-(3), (c)-(5), (d)-(1), (e)-(4)

Class 8 Science Chapter 9 Friction Assertion-Reason Questions

The following questions consist of two statements: Assertion (A) and Reason (R). Answer these questions by selecting the appropriate option given below.

1. Both A and R are true, and R is the correct explanation of A.
2. Both A and R are true, but R is not the correct explanation of A.
3. A is true, but R is false.
4. A is false, but R is true.

Question 1.

Assertion (A): The  Force of friction is smaller on smooth surfaces than on rough surfaces.
Reason (R): Static friction is greater than the sliding friction.

Answer: 2. The  Force of friction is smaller on smooth surfaces than on rough surfaces because on smooth surfaces, the irregularities present are much less compared to rough surfaces.

Question 2.

Assertion (A): Lubricants increase the friction force.
Reason (R): Friction is a necessary evil.

Answer: 4. Lubricants are the materials that minimise the friction force. Friction has advantages as well as disadvantages. That’s why it is called a necessary evil.

Question 3.

Assertion (A) Birds can fly easily in the sky.
Reason (R) Streamlined body helps them in minimizing the friction.

Answer: 1. A body shape that offers a small resistance to the flow of fluid around it, is called streamlined shape. Birds have streamlined shape by nature. That’s why, they fly easily in the air.

Question 4.

Assertion (A) It is difficult to push or pull a heavier object than a lighter object.
Reason (R) Interlocking of irregularities is more prevalent between heavy object surfaces than light object surfaces

Answer: 1. The interlocking of irregularities is more between heavy object surfaces than light object surfaces. That’s why it is difficult to push or pull heavier objects.

The following questions consist of two statements -Assertion (A) and Reason (R). Answer these questions by selecting the appropriate option given below.

1. Both A and R are true, and R is the correct explanation of A.
2. Both A and R are true, but R is not the correct explanation of A.
3. A is true, but R is false.
4. A is false, but R is true.

Question 5.

Assertion (A): We often see that suitcases fitted with wheels are easy to pull.
Reason (R): Rolling friction is smaller than the static and sliding friction.

Answer: 1. Both A and R are true, and R is the correct explanation of A.

Question 6.

Assertion (A): Rocket and aeroplanes has a special body shape, i.e,. streamlined shape.
Reason (R): Streamlined shape helps an object reduce friction drag between the fluid and the object moving through it.

Answer: 1. Both A and R are true, and R is the correct explanation of A.

CBSE Class 8 Science Chapter 8 Force And Pressure Multiple Choice Questions

Question 1. In the figure, two boys, A and B, are shown applying force on a block. If the block moves towards the right, which one of the following statements is correct?

1. The magnitude of force applied by A is greater than that of B.
2. The magnitude of the force applied by A is smaller than that of B.
3. Net force on the block is towards A.
4. The magnitude of force applied by A is equal to that of B

Answer: 1. The Magnitude of force applied by A is greater than that of B.

Question 2. In the circuit shown in the figure, when the circuit is completed, the hammer strikes the gong. Which of the following forces is responsible for the movement of a hammer?

1. Gravitational force alone
2. Electrostatic force alone
3. Magnetic force alone
4. Frictional force alone

Answer: 3. Magnetic force alone

Question 3.

A brick is kept in three different ways on a table, as shown in the figure. The pressure exerted by the brick on the table will be

1. Maximum in position a
2. Maximum in position c
3. Maximum in position b
4. Equal in all cases

Answer: 1. Maximum in position a

Question 4. The figure shows a container filled with water. Which of the following statements is correct about the pressure of water?

1. Pressure at A > Pressure at B > Pressure at C
2. Pressure at A = Pressure at B = Pressure at C
3. Pressure at A < Pressure at B > Pressure at C
4. Pressure at A < Pressure at B < Pressure at C

Answer: 4. Pressure at A < Pressure at B < Pressure at C

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Question 5.

A water tank has four taps fixed at points A, B, C, and D as shown in the figure. The water will flow out at the same pressure from taps at

1. B and C
2. C and D
3. A and B
4. A and C

Answer: 1. B and C

Question 6. P, Q, and Rand S are four solid objects having the same mass. Which object is exerting the least pressure on the table?

1. P
2. Q
3. R
4. S

Answer: 2. Q

Question 7. Type of force where only attraction is found

1. Electrostatic force
2. Magnetic force
3. Gravitational force
4. Both (a) and (b)

Answer: 3. Gravitational force

Question 8. The wear and tear in the machine part is due to

1. Electrostatic force
2. Muscular force
3. Frictional force
4. Gravitational force

Answer: 3. Frictional force

Question 9. Like poles exert a force of

1. Attraction
2. Repulsion
3. Both 1 and 2
4. None of these

Answer: 4. None of these

Question 10. A block of mass 2 kg tied with a rope is going down under the force of gravity of 20 N.

How much force is required by the hand to stop the motion of the block?

1. 10 N
2. 20 N
3. 30 N
4. 40 N

Answer: 2. 20 N

Question 11. When a stone is rotated on a circular path uniformly, the effect of the force will be

1. Change in direction and magnitude of motion.
2. Change in shape of an object.
3. Change in direction of motion only.
4. Change in magnitude only.

Answer: 3. Change in direction of motion only.

Class 8 Science Chapter 8 Force And Pressure Long Answer Type Questions And Answers

Question 1. Two groups of students are playing tug-of-war.

1. Choose the correct direction of force applied by Group Land Group 2.

Answer: 4.

2. Group1 is pulling with a 250 N force, and Group 2 is pulling with a 300 N force. What would be the likely position of the two groups after a minute of pulling?

Answer: 1.  Net 50n Force Demonstration Winning Team Movement

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Question 2. Rishi drops a metal block from the same height onto different wooden blocks of the same mass but different contact areas. The teacher was also watching this activity. He asked Rish some questions to Rish, which are listed below.

Explain the relationship between the contact area of the wooden block and how deeply the wooden block would sink into the soft ground.

A force of 100 N is applied on an area of 4 m 2. Calculate the pressure applied to the area.

The contact area of one of the wooden blocks is 9 cm2. Calculate the force acting on it if the pressure is 900 Pa.

Question 3. Four students wanted to find out who could kick a football the strongest. Each student kicked the football. The table shows the distance the football travelled in the air before hitting the ground.

1. Which student kicked the ball with the greatest force?

1. Student 1
2. Student 2
3. Student 3
4. Student 4

2. Which of these factors must remain the same when each student kicks the football? Choose ‘Yes’ or ‘No’ for the correct response.

Shade the columns in the graph to correctly show the data in the table.

Answer:

As pressure is equal to force divided by area, hence as the contact area of the wooden block increases, the depth to which block would sink into the soft ground decreases.

⇒ \(\text { Pressure }=\frac{\text { Force }}{\text { Area }}\)

Force = 100 N, Area = 4 m2

⇒ \(\text { Pressure }=\frac{\text { Force }}{\text { Area }}=\frac{100}{4}=25Pa\)

The relation between pressure and force is

⇒ \(\text { Pressure }=\frac{\text { Force }}{\text { Area }}\)

Force = Pressure X Area

= (900) (0.0009) ( v 9 cm 2 = 0.0009 m 2 )

= 0.81 N

Question 3. It is much easier to burst an inflated balloon with a needle than with a finger. Explain.
Answer:

Because the needle tip has a very small area of cross-section in comparison to that of our finger, and we know that pressure exerted by a force is inversely proportional to the area where it has been applied, the pressure exerted will be more by the needle tip than the finger.

CBSE Class 8 Science Chapter 4 Combustion And Flame Short Answer Questions

Question 1. We were told that food is a fuel for our bodies. Why?
Answer: The food that we eat is broken down in our body by reaction with oxygen, and energy is produced, which is utilised by our body as a fuel.

Question 2. We have read that the Sun produces its heat and light. Is it also some kind of combustion?
Answer: No, it is not combustion. The heat and light in the Sun are produced by nuclear reactions.

Read And Learn More CBSE Class 8 Science Short Answer Questions

Question 3. Why is it important to know the telephone number of the fire service in your area?
Answer: It is important to know the telephone number of the fire service so that, in case of a fire, the fire brigade can reach on time and extinguish the fire.

Question 4. Why should we never sleep in a room with a burning or smouldering coal fire?
Answer: It is because carbon monoxide gas produced can kill persons sleeping in the room with a burning or smouldering coal fire.

Question 5. If you hold a piece of iron wire with a pair of tongs inside a candle flame or a Bunsen burner flame, what will you observe? Will it produce a flame?
Answer: The Iron wire will become red hot and glow. It will not produce a flame.

Question 6. Boojho wants to separate the following materials as combustible and non-combustible. Can you help him? Charcoal, chalk, stone, iron rod, copper coin, straw, cardboard, glass, paper, candle, wood,
Answer:

1. Combustible — charcoal, straw, cardboard, paper, candle, wood.
2. Non-Combustible- Chalk, Stone, iron rod, copper coil, glass.

CBSE Class 8 Science Chapter 8 Force And Pressure Short Answer Type Questions

Question 1. Two people are applying forces on two opposite sides of a moving cart. The cart still moves with the same speed in the same direction. What do you infer about the magnitudes and direction of the forces applied?
Answer: The magnitude of forces will be equal, and they act in opposite directions, so that they cancel each other. We can understand this by using the following

Question 2. A man is pushing a cart down a slope. Suddenly, the cart starts moving faster, and he wants to slow it down. What should he do?

Answer:

The man can do the following things

1. He can start pulling the cart instead of pushing it to balance the downward force due to gravity.
2. He can go to the other side by moving himself very fast in the direction of motion and try to slow down the speed of the cart by giving an opposite force to the moving cart.

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Question 3. A soccer ball flew towards a goalkeeper standing at the goalpost. He tried to grab it, but it slipped from his hands. Describe the action of the force at the point when the goalkeeper grabbed the ball.

Answer:

When the goalkeeper tried to grab the ball coming towards him, the force he applied caused it to change direction. At the same time, the force caused the ball to decrease in its speed. The force applied did not stop the ball from moving or increase its speed.

Question 4. The figure shows a man with a parachute. Name the force that is responsible for his downward motion. Will he come down with the same speed without the parachute?

Answer:

1. The name of the force responsible for the downward motion of the parachute is called force of gravity.
2. No, because the air friction will become less.

Question 5. In the circuit shown in the figure, when the key is closed, the compass needle placed in the match box deflects. Name the force that causes this deflection.

Answer: On closing the switch, the current starts flowing in the wire, and due to this current, a magnetic field is established around the wire, which exerts a magnetic force on the needle, and it gets deflected.

Question 6. Does the force of gravitation exist between two astronauts in space?
Answer: Yes, there will be a gravitational force between the astronauts because every object in the universe, whether small or large, exerts a force on every other object; it is the universal law of gravitation.

Question 7. The figure shows a car stuck to an electromagnet. Name the forces acting on the car. Which one of them is larger?
Answer:

1. The forces working on the object (car) are
2. Force of gravity (downwards)
3. Magnetic force (upwards)

Since the car is moving upwards, so magnetic force due to the electromagnet is greater.

Class 8 Science Chapter 8 Force And Pressure Very Short Answer Type Questions

Question 1. Where do we apply a force while walking?
Answer: We apply a force on the ground while walking, and the ground applies a reaction force on our foot, due to which we can move forward.

Question 2. Does the palm apply any force on the ball when we place our palm in front of a moving ball?
Answer: Yes, when we place our palm in front of a moving ball, then the palm applies a force on the moving ball and stops it.

Question 3. Name an activity that does not involve any pushing force.
Answer: When a person swims freestyle, he is pulling themselves forward in the water.

Question 4. A ball of dough is rolled into a flat chapati. Name the force exerted to change the shape of the dough.
Answer: The shape of the dough is changed due to the muscular force applied by the hand.

Question 5. In ‘tug of war’, when two teams pull equally hard, what happens?
Answer: In ‘tug of war’, when two teams pull equally hard, then the rope does not move in any direction.

Question 6. A girl is pushing a box towards the East. In which direction should her friend push the box, so that it moves faster in the same direction?
Answer: Her friend should push the box towards the East direction, so that it will start moving faster towards the East because the magnitude of force increases.

Question 7. During dry weather, clothes made of synthetic fibre often stick to the skin. Which type of force is responsible for this phenomenon?
Answer: The electrostatic force starts working between the cloth made of synthetic fibre and sticks to the skin.

Question 8. Two thermocol balls are held close to each other, but they move away from each other when they are released. Name the force which might be responsible for this phenomenon. Explain.
Answer: This is an electrostatic force which is created due to the rubbing, and since the same charges are induced on two balls, they move away from each other.

Question 9. While sifting grains, small pieces fall. Which force pulls them down?
Answer: It is the force of gravity that is responsible for the grains to fall.

Question 10. Does the force of gravity act on dust particles?
Answer: Yes, the force of gravity acts on the dust particles.

Question 11. A gas-filled balloon moves up. Is the upward force acting on it larger or smaller than the force of gravity?
Answer: The upward force will be greater than the force of gravity, then the balloon will be able to lift against this gravitational force.

Question 12. Fruits detached from a tree fall due to the force of gravity. We know that a force arises due to the interaction between two objects. Name the objects interacting in this case.
Answer: The interacting objects in this case are: Earth and fruit. Earth applies a force of gravity on the fruit towards its centre, so the fruit falls.

Question 13. Rahul is pushing a magnet along his table when some paper clips on his table suddenly move. In which direction does the force act on the paper clips?

Answer: As the magnet will attract the paper clips, the force acting on them will be towards the magnet.

Question 14. Under which circumstances, a person not experience any gravitational force?
Answer: A person who is in a space that is too far away from Earth’s gravitational force will not suffer any gravitational force.

Question 15. An astronaut travels from Earth to the moon. How does his weight and mass change?
Answer: The Mass of an object remains constant at all places, so the mass of the astronaut will not change. The weight of an object depends on the gravity; on the moon, gravity is less than on Earth, so the weight of an astronaut will decrease.

Question 16. Have you ever wondered what makes an object slow down or go faster or change its direction of motion?
Answer: Force makes an object slow down or go faster, or change its direction of motion.

Question 17. Paheli remembers that a magnet attracts a piece of iron towards it. Is attraction also a pull? What about repulsion between similar poles of two magnets? Is it a pull or a push?
Answer: The Attraction or repulsion between the poles of a magnet can be seen as another form of pull or push.

Question 18. Does it mean that the net force on an object is zero if the two forces acting on it in opposite directions are equal?
Answer: Yes, when two forces of equal magnitude act in opposite directions, the net force is zero on that body.

Question 19. Boojho has seen children competing with one another in moving a rubber tyre or a ring by pushing it. Why does the speed of the tyre or ring increase whenever it is pushed?
Answer: With every push, they are applying a little more force on the moving tyre in the direction of motion. Hence, the speed of the tyre increases continuously.

Question 20. Does the application of a force always result in a change in the state of motion of the object?
Answer: No, sometimes a heavy material may not move at all, even if you apply the maximum force that you can exert.

Example: When you try to push a wall, no effect of force is observed.