Students rely on Class 8 Science Extra Questions and Class 8 Curiosity Chapter 5 Extra Question Answer Exploring Forces to help self-study at home.
Class 8 Science Chapter 5 Exploring Forces Extra Questions
Class 8 Science Chapter 5 Extra Questions on Exploring Forces
Exploring Forces Class 8 Very Short Question Answer
Question 1.
A child is trying to push a wall with all their strength, but the wall doesn’t move. What does this tell you about the force applied and the resulting motion?
Answer:
A force is applied, but since the wall doesn’t move, the force is balanced by an equal and opposite reaction force from the wall. No unbalanced force means no motion.
Question 2.
You slide a book on a table, and it comes to rest without you touching it again. What invisible force caused the book to Stop? (Competency Based Que.)
Answer:
The frictional force between the book and table surface opposes the motion and gradually slows it down until it stops.
Question 3.
Why is it difficult to walk on a smooth ice surface?
Answer:
Smooth ice offers very little friction, so our feet can’t grip the surface properly, making it hard to walk.
Question 4.
During dry weather, clothes made of synthetic fibre often stick to the skin. Which type of force is responsible for this phenomenon? (NCERT Exemplar)
Answer:
During dry weather, clothes made of synthetic fibre often stick to the skin due to electrostatic force.
Question 5.
Two magnets are brought close with like poles facing each other. They push apart. What kind of force is this?
Answer:
This is a non-contact magnetic force of repulsion, which acts without the magnets touching.
Question 6.
You fill an empty bottle with water and drop it into a bucket. It sinks. You then drop a sealed empty bottle and it floats. What does this experiment tell you about floatation? (Competency Based Que.)
Answer:
The sealed bottle is less dense than water and displaces enough water to experience an upthrust greater than its weight, so it floats. The filled bottle is denser and sinks.
Exploring Forces Class 8 Short Question Answer
Question 1.
A chapati maker is a machine which converts balls of dough into chapati’s. What effect of force comes into play in this process? (NCERT Exemplar)
Answer:
A chapati maker works by pressing balls of dough between two hot plates using force. This applied force flattens the dough, changing its round shape into a flat, circular chapati. This demonstrates that force can change the shape of an object, which is one of the key effects of force.
Question 2.
Two blocks of iron of different masses are kept on a cemented floor as shown in fig. Which one of them would require a larger force to move it from the rest position? (NCERT Exemplar)
Answer:
The 2-unit block would require a larger force to move it from rest. This is because the force of friction between the block and the cemented floor depends on the weight of the object. The block with more mass (2 units) has more weight, which means it presses more against the floor, increasing the normal force and therefore the frictional force. To overcome this larger frictional force and set the block in motion, a greater applied force is required compared to the 1-unit block.
Question 3.
A marble is allowed to roll down an inclined plane from a fixed height. At the foot of the inclined plane, it moves on a horizontal surface (a) covered with silk cloth (b) covered with a layer of sand and (c) covered with a glass sheet. On which surface will the marble move the shortest distance. Give reason for your answer. (NCERT Exemplar)
Answer:
The marble will move the shortest distance on the surface covered with a layer of sand (option b). The layer of sand offers the greatest friction among the three surfaces. Friction opposes motion, and rough surfaces like sand create more resistance, causing the marble to lose its speed quickly and stop sooner. In contrast, silk cloth and especially glass sheet are smoother, offering less friction, so the marble rolls farther on them. Therefore, due to the high frictional force, the marble travels the shortest distance on the sandy surface.
Question 4.
How can you prove that magnetic force is a non-contact force using a simple activity? (Competency Based Que.)
Answer:
Bring a magnet close to some iron nails or paper clips without touching them. As the magnet approaches, the nails start moving towards it. This happens even though there is no direct contact between the magnet and the nails. This shows that magnetic force can act from a distance and hence, it is a non-contact force.
Question 5.
How does the distance between a magnet and an object affect the magnetic force acting on the object?
Answer:
Magnetic force decreases with increasing distance. The closer the object is to the magnet, the stronger the force it experiences. If the object is too far, the magnetic force may become too weak to act.
Question 6.
Why do we sometimes feel a small electric shock after walking on a carpet and touching a metal object?
Answer:
While walking on a carpet, our body may accumulate electric charges due to the friction between our feet and the carpet surface. This builds up a static charge on our body. When we touch a metal object, the excess charge suddenly moves from our body to the conductor (metal), causing a small spark or discharge. This sudden movement of charges is felt as a mild electric shock and it is due to electrostatic force.
Question 7.
Why do two plastic straws, rubbed with a cloth, repel each other when brought close?
Answer:
When two plastic straws are rubbed with the same cloth, they acquire the same type of electric charge (either both positive or both negative). Like charges repel each other due to the” nature of electrostatic force. So, when the straws are brought close, they push away from each other. This behavior is a result of electrostatic repulsion, which is a non-contact force.
Question 8.
Does force of gravity act on dust particles? (NCERT Exemplar)
Answer:
Yes, the force of gravity does act on dust particles. Even though dust particles are very light, they still have mass. And any object with mass experiences gravitational force. On Earth, gravity pulls dust particles downward, which is why they eventually settle on surfaces if not disturbed by air currents.
Question 9.
A gas filled balloon moves up. Is the upward force acting on it larger or smaller than the force of gravity? (NCERT Exemplar)
Answer:
A gas-filled balloon moves up because the upward force (buoyant force) acting on it is larger than the downward force of gravity (its weight). This imbalance causes the balloon to rise. When the upthrust is greater than the weight, the object moves upward.
Question 10.
Why does a wooden log float on water but an iron nail sinks, even if both are placed gently on the water surface?
Answer:
A wooden log floats because the buoyant force acting on it is greater than or equal to its weight due to its lower density. An iron nail sinks because its density is much higher than water, so the upward buoyant force cannot balance its weight.
Exploring Forces Class 8 Long Question Answer
Question 1.
(i) Two friends are trying to push a heavy load as shown in fig. Why is it difficult for them to push the load?
(ii) Suggest a way which will make this task easier for them. (NCERT Exemplar)
Answer:
(i) The load is heavy, so it has a large mass and therefore a large inertia (resistance to motion). There is friction between the surface and the load, which opposes their push. Since they are pushing with less mechanical advantage (no tools used), more effort is required to move it.
(ii) Use rollers, wheels or trolleys to reduce friction between the load and the ground. Apply lubricants to the surface to decrease resistance. Use inclined planes or pulleys to gain mechanical advantage. Both friends can push in the same direction at the same time to combine their forces effectively.
Question 2.
An archer shoots an arrow in the air horizontally.
However, after moving some distance, the arrow falls to the ground. Name the initial force that sets the arrow in motion. Explain, why the arrow ultimately falls down. (NCERT Exemplar)
Answer:
The initial force that sets the arrow in motion is the muscular force applied by the archer. When the archer pulls back the string of the bow and releases it, the tension created in the string gets transferred to the arrow. This muscular force gives the arrow an initial push in the forward (horizontal) direction, setting it into motion.
However, once the arrow is released and begins to move through the air, it is no longer in contact with the archer. But that doesn’t mean no force acts on it. The force of gravity, a non-contact force, continuously pulls the arrow downward toward the Earth. Although the arrow has horizontal motion due to the muscular force, the vertical motion (falling down) is caused by gravity.
As a result of these two forces, horizontal muscular force at the start and continuous vertical gravitational force, the arrow follows a curved path (called a projectile path) and eventually falls to the ground. Thus, even though it was shot horizontally, it cannot keep moving in a straight line because the Earth’s gravitational force pulls it down throughout its flight.
Question 3.
You are given a bar magnet and a few unknown metal objects. Design an activity to identify which objects are magnetic. What observations will you make and what conclusions can you draw? (Competency Based Que.)
Answer:
To identify magnetic materials, bring the bar magnet near each object like a nail, coin, screw, plastic cap, and key. If the object moves toward the magnet, it is magnetic (like the nail or key). If it shows no reaction, it is non-magnetic (like plastic). This activity helps conclude that magnetic force acts only on specific materials such as iron, nickel and cobalt. The attractive force acts even without contact, making it a non-contact force.
Question 4.
You rub a plastic scale on your shirt and bring it near dry, light objects like bits of paper. They get attracted and stick to it. But after some time, they fall off. Why does this happen? (Competency Based Que.)
Answer:
Rubbing transfers charge to the plastic scale, enabling it to attract small objects due to electrostatic force. However, over time, the charge leaks away into the air or neutralizes due to moisture or contact. Once the scale loses its charge, the electrostatic force weakens, and the objects fall off. This shows that electrostatic effects are temporary and require insulating materials and dry conditions to be observable.
Question 5.
You are swimming in a pool and you feels lighter in water than on land.
(i) What is the reason behind this sensation?
(ii) Name the force responsible and explain how it acts.
(iii) Also, relate this to the concept of upthrust.
Answer:
(i) When we are in water, we feel lighter because water pushes upward on our body. This upward push reduces our apparent weight, so we feel less heavy than on land.
(ii) The force is called upthrust or buoyant force. It act because water pressure increase with depth. The bottom part of the body experiences more pressure than the top, creating a net upward force.
(iii) According to Archimedes’ principle, in water, our body displaces water and this displaced water’s weight equals the upthrust. This upward force makes us feel lighter.
Exploring Forces Class 8 Case Based Questions
Question 1.
Riya is participating in her school’s science exhibition. She decides to demonstrate the role of friction in our daily life. She sets up a ramp and rolls different objects (a wooden block, a steel ball, and a rubber ball) down the ramp. She also covers the ramp with different materials-smooth plastic sheet, sandpaper, and a towel-one after the other and records how far each object moves after coming down the ramp.
She observes that the steel ball rolls the farthest on the plastic sheet and the rubber ball moves the shortest distance on the sandpaper. She concludes that friction varies depending on the surface and the Object involved. (Competency Based Que.)
(i) Why did the steel ball move farther on the plastic sheet compared to the rubber ball on sandpaper? What does this tell us about friction?
(ii) Riya wants to reduce the friction further on the ramp to allow the objects to slide more easily. What method can she use and how will it affect the motion of the objects?
(iii) Even though friction opposes motion, Riya mentions in her report that it is a necessary force. Explain why friction is both helpful and unwanted in nature.
Answer:
(i) The steel ball moved farther on the plastic sheet because the plastic sheet offers very little resistance or friction to the ball’s motion. In contrast, the rubber ball on sandpaper experienced greater friction, which quickly reduced its speed and stopped it in a shorter distance. This demonstrates that smoother surfaces create less friction, while rough surfaces create more friction, slowing down moving objects more quickly. It shows that friction depends on the nature of the surface in contact.
(ii) Riya can apply oil, grease, or powder (like talcum powder) on the ramp to reduce friction. This is called lubrication. Lubricants fill the tiny gaps between surfaces and make them smoother, which reduces the contact and resistance between the ramp and the objects. As a result, the objects will slide or roll more freely and cover longer distances, because the resisting force of friction is minimized.
(iii) Friction opposes motion, which can make it harder to move objects. However, it is also essential in our daily life. For example:
(a) Walking or driving would not be possible without friction between our shoes or tires and the ground.
(b) It helps us grip objects and write using a pen or pencil.
(c) It allows brakes in vehicles to function and stop them safely.
So, although friction can reduce efficiency by causing wear and heat, it is crucial for control and safety. Thus, friction is considered a necessary evil, we often need to manage it, not completely eliminate it.
Question 2.
Rohan went to the village pond during summer vacation and noticed something strange. When he tried to pull a bucket full of water out of the pond, it felt lighter under water, but as soon as it came out of the water, it suddenly felt much heavier.
Curious, he dipped a plastic bottle filled with air into the water, and saw it float back up. When he filled the same bottle with water and pushed it in, it sank. This made him wonder how objects behave differently in water and what force is responsible for it.
(i) Why did the bucket feel lighter when it was submerged in water but heavier when it came out? Name and explain the force responsible.
(ii) Why did the empty plastic bottle float while the water-filled bottle sink? What does this tell us about the relation between upthrust and weight?
(iii) How is the concept of upthrust useful in real-life applications? Give two examples based on the observations Rohan made.
Answer:
(i) The bucket felt lighter under water because of the upward force exerted by water on the bucket. This upward force is called upthrust or buoyant force. Upthrust acts in the opposite direction to gravity, so it partially cancels out the weight of the object when submerged. Once the bucket is taken out of water, this upthrust disappears and the entire weight is felt, making it feel heavier.
(ii) The empty plastic bottle is filled with air, making its average density less than that of water. Therefore, the upthrust acting on it is greater than its weight, and it floats. On the other hand, the water-filled bottle has a density equal to or more than water, so the upthrust is not enough to balance its weight, causing it to sink. This shows that whether an object floats or sinks depends on the balance between upthrust and the object’s weight.
(iii) The concept of upthrust is widely used in real-life situations.
(a) Ships and boats are designed with hollow bases to ensure that their average density is less than water, allowing them to float due to buoyant force.
(b) Submarines control their depth by adjusting the amount of water in their tanks, which changes their overall density and hence the effect of upthrust.
Rohan’s observation with the bottle shows the basic principle behind these technologies, how controlling weight and volume affects floating and sinking due to upthrust.
Skill Based Questions
Question 1.
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 air before hitting the ground. Thinking skin
| Student 1 | Student 2 | Student 3 | Student 4 | |
| Distance the ball travelled in air before hitting the ground | 10 m | 12 m | 8 m | 14 m |
(i) Which student kicked the ball with the greatest force?
(a) Student 1
(b) Student 2
(c) Student 3
(d) Student 4
(ii) Shade the columns in the graph to correctly show the data in the table.
(iii) Which of these factors must remain the same when each student kicks the football? Choose Yes or No for the correct response.
| Factor that must remain the same | Yes or No |
| Type of ground surface | Yes/No |
| Direction and speed of the wind | Yes/No |
| Size of the shoe worn by the student | Yes/No |
Question 2.
Raju wanted to find out which one of flour surfaces produces the greatest friction. He pushed the same toy car on the four surfaces, separately.
Raju noted the distance travelled by car on each surface before stopping.
| (a) Surface 1 | (b) Surface 2 | (c) Surface 3 | (d) Surface 4 | |
| Distance travelled by the toy car before stopping | 120 cm | 150 cm | 100 cm | 180 cm |
(i) On which surface did the car experience the greatest
(a) Surface 1
(b) Surface 2
(c) Surface 3
(d) Surface 4
(ii) What must be kept the same in the activity to compare the distances travelled by the car?
………………………………………………
……………………………………………..
(iii) What will happen to the car if it continues to move on the surface for 1 hour.
(a) The wheels will get hard.
(b) The wheels will becomes hot
(c) The wheels will shrink in size
(d) The wheels will change shape.
Question 3.
You are given the following materials
• A bar magnet
• A sheet of paper
• Some iron nails
• A plastic ruler
• A wooden block
You are asked to place the sheet of paper on the table and hide the bar magnet under it. Then, you sprinkle the iron nails on top of the sheet. (Application Based Que.)
(i) Observe and explain what happens to the iron nails.
(ii) Identify the force acting on the nails and explain how it works through the paper.
(iii) Predict and justify whether the same effect will be observed if you replace the iron nails with pieces of aluminium foil.
Question 4.
You are given the following materials
• A plastic bottle (with cap)
• A bucket filled with water
• Small stones or marbles
• A weighing scale
• A notebook for observations
You are asked to perform the following activity and answer the related questions.
Activity
(i) Place the empty plastic bottle in the bucket of water. Observe what happens.
(ii) Now slowly place stones/marbles into the bottle, one by one and observe how the bottle behaves.
(iii) Continue adding until the bottle starts to sink.
Tasks
(i) What force causes the empty bottle to float? Name and define it.
(ii) As you add stones, explain why the bottle begins to sink. What changes in the balance of forces acting on it?
(iii) How does this activity demonstrate the concept of upthrust and buoyant force?
(iv) If the same bottle is filled with oil and placed in water, what will happen? Why? (Application Based Que.)
Exploring Forces Extra Questions for Practice
Very Short Answer Type Questions
Question 1.
Which force is used when we squeeze a toothpaste tube and what change does it produce?
Question 2.
If two people pull a rope with equal force in opposite directions and the rope doesn’t move, what can you say about the net force?
Question 3.
Why do we use wheels or rollers while shifting heavy loads?
Question 4.
How can you demonstrate that electrostatic force can act without direct contact?
Question 5.
What is the direction of the force of buoyancy acting on a floating object?
Short Answer Type Questions
Question 1.
If friction is a contact force, how can you reduce it without touching the object?
Question 2.
How does gravitational force help in the formation of rain?
Question 3.
How does charging by rubbing work in everyday materials?
Question 4.
How does the shape of a boat help it float?
Question 5.
Why does a sealed empty plastic bottle float on water but sinks when filled with water?
Long Answer Type Questions
Question 1.
While walking on a polished marble floor with wet feet, you are more likely to slip than on a rough surface. Explain, why this happens. How does friction vary on different surfaces? Describe an activity to prove your observation.
Question 2.
Two inflated balloons hung close to each other on threads move apart when rubbed with wool. Which force is acting here? How can you perform this activity at home or in school to show electrostatic repulsion? What does it tell us about like charges?
Question 3.
You observe that an inflated balloon released from your hand quickly rises in the air. Explain this observation in terms of forces acting on the balloon. What are the different forces at play? Describe how you can verify the presence of each of them through simple activities.