KSEEB Solutions For Class 8 Science Chapter 7 Force And Pressure

KSEEB Solutions Class 8 Science Chapter 7 Force And Pressure Points To Remember

Force:

A push or a pull, that changes or tends to change the state of rest or of uniform motion of an object or changes its direction or shape.

A force arises due to the interaction between two objects.

Force has magnitude as well as direction. The SI unit of force is Newton.

A change in the speed of an object or the direction of its motion or both implies a change in its state of motion.

Force acting on an object may cause a change in its state of motion or a change in its shape.

A force can act on an object with or without being in contact with it.

Types of Forces:

Contact Forces: The forces act on a body when the source of force is in actual contact with the body. The point where the force is applied on an object is called the point of application of force
1. Muscular Force: The force exerted by the muscles of the body. We make use of the muscular force of animals like bullocks, horses, and camels to get our activities done.
2. Mechanical Force: The force produced by a machine.
3. Frictional Force: The force that opposes the motion of an object.

Non-Contact Forces: Forces that do not involve physical contact between two bodies on which they act.
1. Magnetic Force: A magnet exerts a noncontact force on objects made of iron, steel, cobalt, or nickel.
2. Electrostatic Force: The force which results due to the repulsion of similar charges or attraction of opposite charges.
3. Gravitational Forces: The force that exists between any two bodies by virtue of their mass.

Pressure:

Thrust acting per unit surface area is called pressure. Thrust s the force acting on an object perpendicular to its surface. In the SI system, pressure is measured in newton per square meter which is equal to (1) pascal (Pa).

Like solids, fluids (liquids and gases) also exert pressure. A solid exerts pressure only in the downward direction due to its weight, whereas liquids and gases exert pressure in all directions. Hence liquids and gases exert pressure on the walls of their container.

The thick blanket of air that covers the earth is termed the atmosphere. The pressure exerted by the atmosphere is called atmospheric pressure. The tremendous atmospheric pressure surrounding us is not felt by us because the fluid pressure inside our bodies counterbalances the atmospheric pressure around us.

Kseeb Solutions For Class 8 Science Chapter 7 Force And Pressure Pdf

Force And Pressure NCERT Textbook Exercises

Question 1. Give two examples of each of the situations in which you push or pull to change the state of motion of objects.
Answer:

If a rubber ball or marble is placed on a very smooth surface and given a small push, it starts moving with some speed.

If a child is placed on a hanging swing in the state of rest and the swing is pulled again and again by a rope, the swing will move to and fro with a speed.

Question 2. Give two examples of situations in which applied force causes a change in the shape of an object.
Answer:

If an inflated balloon is taken and pressed from two sides with a hand, its shape gets changed.

If a plate of steel is beaten up with a hammer the shape of the plate will get change.

Question 3. Fill in the blanks in the following statements.
1. To draw water from a well we have to pull at the rope.
2. A charged body attracts an uncharged body toward it.
3. To move a loaded trolley we have to pull it.
4. The north pole of a magnet repels the north pole of another magnet.

Question 4. An archer stretches her bow while taking aim at the target. She then releases the arrow, which begins to move towards the target Based on this information fill up the gaps in the statements using the following terms.
Muscular, contact, non-contact, gravity, friction, shape, attraction
1. To stretch the bow, the archer applies a force that causes a change in its______
2. The force applied by the archer to stretch the bow is an example of _______force.
3. The type of force responsible for a change in the state of motion of the arrow is an example of a _____ force.
4. While the arrow moves towards its target, the forces acting on it are due _____to ______ and that due to air.
Answer:
1. Shape
2. Muscular
3. Contact
4. Gravity, friction.

Karnataka Board Class 8 Science Chapter 7 Solutions

Question 5. In the following statements identify the agent exerting the force and object on which its acts. State the effect of the force in each case.
1. Squeezing a piece of lemon between the fingers to extract its juice.
2. Take out paste from a toothpaste tube.
3. A load is suspended from a spring while its other end is on a hook fixed to a wall.
4. An athlete making a high jump to clear the bar at a certain height.
Answer:
Agents exerting force

1. Fingers
   
2. Fingers
   
3. A load
4. An athlete

The object on which force acts

1. Lemon
   
2. Toothpaste tube
   
3. Spring
   
4. On the legs

Effect of force

1. Lemon juice is extracted
   
2. Toothpaste come out
   
3. The spring expands
   
4. Cleans the height

Question 6. A blacksmith hammers a hot piece of iron while making tools. How does the force due to hammering affect the piece of iron?
Answer: The shape of the hot piece of iron changes. It flattens and becomes thinner than earlier. This is the effect of force due to hammering the piece of iron.

Question 7. An inflated balloon was pressed against a wall after it has been rubbed with a piece of synthetic cloth. It was found that the balloon sticks to the wall. What force might be responsible for the attraction between the balloon and the wall?
Answer: This is an electrostatic force.

Question 8. Name the forces acting on a plastic bucket containing water held above ground level in your hand. Discuss why the forces acting on
the bucket does not bring a change in its state of motion.
Answer: The forces that act on the bucket are as follows:
1. The pressure of water contained in it, exerted on its wall and on the base of the bucket.
2. Force of gravity by the earth
3. The water is contained in a bucket and the pressure of force is exerted on the wall of the bucket, which is sufficient to take it as a force. As the bucket is held in my hand, so I overcome the force of gravity of the earth. That is why these forces do not bring a change in the state of motion.

Question 9. A rocket has been fired upwards to launch a satellite in its orbit. Name the two forces acting on the rocket immediately after leaving the launching pad.
Answer: The two forces that are acting on the rocket immediately after leaving the launching pad are:

Force of gravity of the earth acting downward and

The frictional force produced by air particles.

Force And Pressure Class 8 Kseeb Solutions With Answers

Question 10. When we press the bulb of a dropper with its nozzle kept in water, the air in the dropper is seen to escape in the form of bubbles. Once we release the pressure on the bulb, water gets filled in the dropper. The rise of water in the dropper is due to
1. Pressure of water.
2. Gravity of the earth.
3. Shape of a rubber bulb.
4. Atmospheric pressure.
Answer: 4. Atmospheric pressure.

KSEEB Class 8 Science Chapter 7 Force And Pressure Questions 

Force And Pressure Activities

Question 1. Gives some examples of familiar situations involving the motion of objects. You can add more such situations or replace those given here. Try to identify the activities involved in each case as a push and/or a pull and record your observations. One example has been given to help you. Identifying Actions as Push or Pull
Answer:

Question 2. Choose a heavy object like a table or a box, which you can move only by pushing hard. Try to push it all by yourself. Can you move it? Now ask one of your friends to help you in pushing it in the same direction Is it easier to move it now? Can you explain why? Now push the same object, but ask your friend to push it from the opposite side Does the object move? If it does, note the direction in which it moves. Can you guess which one of you is applying a larger force?
Answer:
1. The box moves with difficulty when we push alone but moves easily if helped by our friend. Thus, force applied to an object in the same direction adds to one another.
2. When the object is pushed from the opposite side, it does not move. Thus, if two forces act in the opposite direction on an object the net force acting on it is the difference between the two forces.

Question 3. Take a rubber ball and place it on a level surface such as a tabletop or a concrete floor. Now, gently push the ball along the level surface Does the ball begin to move? Push the ball again while it is still moving. Is there any change in its speed? Does it increase or decrease? Next, place your palm in front of the moving ball. Remove your palm as soon as the moving ball touches it. Does your palm apply force on the ball? What happens to the speed of the ball now? Does it increase or decrease? What would happen if you let your palm hold the moving ball?

Answer: When we push the ball along the level surface, the ball begins to move. When we push the ball again while it is still moving, increases its speed. When we place our palm in front of the moving ball, decreases its speed. Hence, the force can change the state of motion.

Kseeb Class 8 Science Force And Pressure Exercise Solutions

Question 4. Take a ball and place it on a level surface as you did Make the ball move by giving it a push. Now place the ruler from your geometry box in its path In doing so, you would apply a force on the moving ball. Does the ball continue to move in the same direction after it strikes the ruler? Repeat the activity and try to obstruct the moving ball by placing the ruler such that it makes different angles to its path. In each case note your observations about the direction of motion of the ball after it strikes the ruler.
Answer: The ball changes direction after it strikes the ruler. Thus, a force can change the direction of motion of a moving object.

• A ball is set in motion by pushing it along a level surface and
• The direction of motion of the ball after it strikes the ruler placed in its path

Question 5. Some situations have been given in Column in which objects are not free to move. Column 2 of the Table suggests the manner in which a force can be applied to each object while Column 3 shows the action. Try to observe the effect of the force in as many situations as possible. You can also add similar situations using available material from your environment. Note your observations in Columns 4 and 5.
Answer: From the above actions, we can conclude that force can change the shape of an object.

Karnataka Board 8th Science Chapter 7 Important Questions And Answers

Question 6. Take a pair of bar magnets. Place the longer side of one of the magnets over three round-shaped pencils or wooden rollers as shown in Fig. 11.4. Now bring one end of the other magnet near the end of the magnet placed on the rollers. Make sure that the two magnets do not touch each other. Observe what happens. Next, bring the other end of the magnet near the same end of the magnet placed on the rollers Note what happens to the magnet placed on the rollers every time another magnet is brought near it.
Answer: When unlike poles of the magnet are brought near the other magnet, they attract each other and move in the direction of another magnet. When like poles of a magnet are brought near to the other magnet, they repel each other and move in the direction away from the other magnet. Thus, the force exerted by a magnet on another magnet is a type of non-contact force.

Question 7. Take a plastic straw and cut it into nearly two equal pieces. Suspend one of the pieces from the edge of a table with the help of a piece of thread Now hold the other piece of straw in your hand and rub its free end with a sheet of paper. Bring the rubbed end of the straw near the suspended straw. Make sure that the two pieces do not touch each other. What do you observe? Next, rub the free end of the suspended piece of straw with a sheet of paper. Again, bring the piece of straw that was rubbed
earlier with paper near the free end of the suspended straw. What do you observe now?
Picture
Answer: A straw rubbed with paper attracts another straw but repels it if it has also been rubbed with a sheet of paper. The force exerted by a charged body on another charged or uncharged body is known as electrostatic force.
Question 8. Take a transparent glass tube or a plastic pipe. The length of the pipe/tube should be about 15 cm and its diameter should be 5-7.5 cm. Also, take a piece of a thin sheet of good quality rubber, say, a rubber balloon. Stretch the rubber sheet tightly over one end of the pipe. Hold the pipe in the middle, keeping it in a vertical position. Ask one of your friends to pour some water into the pipe. Does the rubber sheet bulge out? Note also the height of the water column in the pipe. Pour some more water. Observe again the bulge in the rubber sheet and the height of the water column in the pipe. Repeat this process a few more times. Can you see any relation between the amount of the bulge in the rubber sheet and the height of the water column in the pipe?
Answer: The amount of bulge in the rubber sheet increases with the height of the water column in the pipe. Thus, the pressure exerted by water at the bottom of the container depends upon the height of its column.

Question 9. Take a plastic bottle. You can take a discarded water or soft drink bottle. Fix a cylindrical glass tube, a few cm long near its bottom You can do so by slightly heating one end of the glass tube and then quickly inserting it near the bottom of the bottle. Make sure that the
water does not leak from the joint. If there is any leakage, seal it with molten wax. Cover the mouth of the glass tube with a thin rubber sheet as you did it. Now fill the bottle up to half with water. What do you observe? Why does the rubber sheet fixed to the glass tube bulge this time? Pour
some more water into the bottle. Is there any change in the bulge’ of the rubber sheet? Answer: Yes, the rubber tube bulge out, and the bulging increases with the amount of water in the bottle. Thus, liquid exerts pressure on the walls of the container.

Question 10. Take an empty plastic bottle or a cylindrical container. You can take a used tin of talcum powder or a plastic bottle. Drill four holes all around near the bottom of the bottle. Make sure that the holes are at the same height from the bottom Now fill the bottle with water. What do you observe? Do the different streams of water coming out of the holes to fall at the same distance from the bottle? What does this indicate?
Answer: We observed different streams of a waterfall at the same distance from the bottle. Thus, it indicates that liquids exert equal pressure at the same depth.

Question 11. Take a good quality rubber sucker. It looks like a small rubber cup Press it hard on a smooth plane surface. Does it stick to the surface? Now try to pull it off the surface. Can you do it?

Answer: When we press the sucker, most of the air between its cup and the surface escapes. The sucker sticks to the surface because the pressure of the atmosphere acts on it. To pull the sucker off the surface, the applied force should be large enough to overcome the atmospheric pressure. Thus, this activity gives us an idea about the magnitude of atmospheric
pressure.

Kseeb Class 8 Science Chapter 7 Textbook Solutions

Force And Pressure Additional Questions

Question 1. A ball of dough is rolled into a flat chapatti.
Name the force exerted to change the shape of the dough.
Answer: Muscular force

Question 2. Where do we apply a force while walking?
Answer: While walking we apply force on the ground.

Question 3. What is the name of the instrument used to measure atmospheric pressure?
Answer: Barometer

Question 4. Give two examples of contact force.
Answer: Muscular force, the force of friction.

Question 5. What kind of force is an electrostatic force?
Answer: Non-contact force

Question 6. What do you mean by magnitude?
Answer: The strength of a force is usually expressed by its magnitude.

Question 7. How do fluids exert pressure?
Answer: Fluids exert pressure in all directions. Fluids also exert pressure on the walls of the container that hold them.

Question 8. A force of 100 N is applied on an area of 4m² Compute pressure is applied on the area.
Answer: Given: Force = 100 N, Area = 4n²
Pressure = Force /Area =100/4 = 25pa.

Question 9. What is the similarity between electrostatic and magnetic forces?
Answer:

Both are non-contact forces.

Both are attractive as well as repulsive forces.

Question 10. What are the effects of force on an object?
Answer:

Force can change the state of motion of an object.

Force changes the speed of a moving object.

Force can cause an object to turn or change direction.

Force can change the shape of an object.

Kseeb 8th Standard Science Chapter 7 Notes And Solutions

Question 11. State the difference between contact force and non-contact force.
Answer:
Contact force

The force that can be applied only when it is in contact with an object is called a contact force. Examples: muscular force, and frictional force.

Non-contact force

The force exerted on an object without touching it is known as non-contact force. Examples: gravitational force, and magnetic force.

Question 12. Why it is easier to walk on soft sand if we have flat shoes rather than shoes with sharp heels (or pencil heels)?
Answer: A flat shoe has a greater area in contact with the soft sand and exerts less pressure on the soft ground. Due to this, the flat’ shoes do not sink much in soft sand and it is easy to walk on them. On the other hand, a sharp heel has a small area in contact with the soft sand and exerts greater pressure on the sand. Due to this, the sharp heels sink deep into soft sand making it difficult for the wearer to walk on them.

Force And Pressure Class 8 KSEEB Exercise Solutions 

Force And Pressure Activity

Question 1. Take a tumbler and fill it with water. Cover the mouth of the tumbler with a thick card similar to that of a postcard. Hold the tumbler with one hand while keeping the card pressed to its mouth with your other hand. Turn the tumbler upside down while keeping the card pressed tots mouth. Make sure that the tumbler is held vertically. Gently remove the hand pressing the card. What do you observe? Does the card get detached allowing the water to spill? With a little practice, you will find that the card continues to hold water in the tumbler even after it is not supported by your hand. Also, try this activity by using a piece of cloth to hold the tumbler in an upside-down position.
Answer: Question 2. Make a 50cm x 50cm bed of dry sand about 10cm in thickness. Make sure that its top surface is leveled. Take a wooden or a plastic stool. Cut two strips of graph paper each with a width of 1 cm. Paste them vertically on any leg of the stool—one at the bottom and the other from the top. Now gently put the stool on the sand bed with its legs resting on the sand. Increase the size of the sand bed if required. Now put a load, say a school bag full of books, on the seat of the stool. Mark the level of sand on the graph strip. This would give you the depth, if any, to which the legs of the stool sink in the sand. Next, turn the stool upside down so that now it rests on its seat on the sand bed. Note the depth to which the stool sinks now. Next, put the same load on the stool and note the depth to which it sinks in the sand. Compare the pressure exerted by the stool in the two situations.
Answer: Pressure exerted by the stool is greatest in the first situation.

Multiple Choice Questions

Question 1. Two boys A and B are shown applying force on a block. If the block moves toward 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 force applied by A is smaller than that of B.
3. The net force on the block is towards A.
4. The magnitude of force applied by A is equal to that of B.
Picture
Answer: 1. Magnitude of force applied by A is greater than that of B.
Explanation: The magnitude of force applied by 1 is bigger than that of B as a result of the block moves towards the right i.e. towards 2.

Question 2. When the circuit is completed, the hammer strikes the gong. Which of the following force is responsible for the movement of the hammer?
1. Gravitational force alone
2. Electrostatic force alone
3. Magnetic force alone
4. Frictional force alone

Answer: 3. Magnetic force alone
Explanation: As electric current flows through the coil it behaves like an electromagnet which creates magnetic force. Hence the answer is magnetic force alone.

Question 3. During dry weather, while combing hair, sometimes we experience hair flying apart. The force responsible for this is
1. Force of gravity.
2. Electrostatic force.
3. The force of friction.
4. Magnetic force.
Answer: 2. Electrostatic force.
Explanation: On combing the hair, the comb and hair get oppositely charged due to electrostatic force.

Question 4. A container filled with water. Which of the following statements is correct about the pressure of water?
1. The pressure at A> Pressure at B > Pressure at C.
2. The pressure at A= Pressure at B = Pressure at C.
3. The pressure at A< Pressure at B > Pressure at C.
4. The pressure at A< Pressure at B.
Answer: 4. The Pressure at A< Pressure at B
Explanation: An increase in water leads to an increase in depth.

Question 5. Two objects repel each other. This repulsion could be due to
1. Frictional force only
2. Electrostatic force only
3. Magnetic force only
4. Either a magnetic or an electrostatic force
Answer: 4. Either a magnetic or an electrostatic force
Explanation: when two objects are experiencing repulsive force because there may be an electrostatic force or a magnetic force.

Step-By-Step Solutions For Force And Pressure Class 8 Karnataka Board

Question 6. Which one of the following forces is a contact force?
1. Force of gravity
2. Force of friction
3. Magnetic force
4. Electrostatic force
Answer: 2. Force of friction
Explanation: Force of attraction acts only when the bodies are in contact.

Question 7. A water tank has four taps fixed at points A, B, C, and D in Fig. The water will flow out at the same pressure from the taps at
1. B and C
2. A and B
3. C and D
4. A and C
Answer: 1. B and C
Explanation: B and C are at the same level, hence pressure will be the same at B and C.

Question 8. A girl is pushing a box in the east direction. In which direction should her friend push the box so that it moves faster in the same direction?
Answer: Towards the east.

Question 9. In the circuit, when the key is closed, the compass needle placed in the matchbox deflects. Name the force which causes this deflection.
Answer: Magnetic force.

Question 10. During dry weather, clothes made of synthetic fiber often stick to the skin. Which type of force is responsible for this phenomenon?
Answer: Electrostatic force

Question 11. While sieving grains, small pieces fall down. Which force pulls them down?
Answer: Force of gravity.

Question 12. Does the force of gravity act on dust particles?
Answer: Yes, the force of gravity act on dust particles.

Question 13. 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 is larger than the force of gravity.

Question 14. Does the force of gravitation exist between two astronauts in space?
Answer: Yes, the force of gravitation exists between two astronauts in space.

Question 15. A chapati maker is a machine that converts balls of dough into chapati. What effect of force comes into play in this process?
Answer: Force works on the dough to convert it to chapati.

Question 16. Shows a man with a parachute. Name the force which is responsible for his downward motion. Will he come down at the same speed without the parachute?
Answer: Force of gravity is responsible for his downward motion. If he comes down without a parachute his speed will be higher.

Question 17. Two persons are applying forces on two opposite sides of a moving cart. The cart still moves at the same speed in the same direction. What do you infer about the magnitudes and direction of the forces applied?
Answer: Force applied is of equal magnitude in the opposite direction hence the cart moves with the same speed in the same direction.

Question 18. Two thermocouple balls held close to each other move away from each other. When they are released, name the force which might be responsible for this phenomenon. Explain.
Answer: Two Thermocol balls held close to each other move away from each other, which is because of electrostatic force. The balls having similar charges move away due to repulsion between similar charges.

Question 19. Fruits detached from a tree fall down 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: Earth and fruits.

Question 20. Aman 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: He should apply force to pull the cart up the slope.

Question 21. Shows a car sticking to an electromagnet. Name the forces acting on the car. Which one of them is larger?

Answer:

Magnetic force (in the upward direction) force of gravity or the weight of the car (downward) act once.

Magnetic force is larger than the force of gravity.

Karnataka State Board Syllabus for Class 8 Textbooks Solutions

• Chapter 1 Crop Production and Management
• Chapter 2 Microorganisms: Friend and Foe
• Chapter 3 Synthetic Fibres and Plastics
• Chapter 4 Materials: metals and Non-Metals
• Chapter 5 Coal and Petroleum
• Chapter 6 Conservation of Plants and Animals
• Chapter 8 Friction
• Chapter 9 Sound
• Chapter 10 Combustion and Flame
• Chapter 11 Cell Structure and Functions
• Chapter 12 Reproduction in Animals
• Chapter 13 Reaching the age of Adolescence
• Chapter 14 Chemical Effects of Electric Current
• Chapter 15 Some Natural Phenomena
• Chapter 16 Light
• Chapter 17 Stars and the Solar System
• Chapter 18 Pollution of Air and Water