Class 8 Science Curiosity Chapter 5 Solutions (NCERT 2026–27) – Exploring Forces

These Class 8 Science Curiosity Chapter 5 solutions cover Exploring Forces from the new NCF-2023 textbook (2026–27), with the “Probe and ponder” prompts, in-text activities and every “Keep the curiosity alive” exercise question answered step by step.

Class: 8 Subject: Science Book: Curiosity Chapter: 5 Exercise: Keep the curiosity alive (10 Qs) Session: 2026–27
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Class 8 Science Curiosity Chapter 5 Solutions – Overview

Chapter 5 of Curiosity, Exploring Forces, introduces force as a push or pull resulting from the interaction of two or more objects, measured in the SI unit newton (N). It shows how a force can make an object move, change its speed or direction of motion, or change its shape. The chapter then classifies forces into contact forces (muscular force and friction) and non-contact forces (magnetic, electrostatic and gravitational force), explains weight and its measurement with a spring balance, distinguishes weight from mass, and ends with buoyant force (upthrust) and the ideas of floating and sinking. These Class 8 Science Curiosity Chapter 5 solutions answer every textbook question step by step.

Key Concepts & Definitions

Force: a push or pull on an object resulting from the object’s interaction with another object. The SI unit of force is the newton (N); at least two objects must interact for a force to come into play.

Effects of force: a force may make an object move from rest, change its speed, change its direction of motion, change its shape, or cause some or all of these.

Contact forces: act only when two objects are in physical contact — e.g. muscular force (from the action of muscles) and friction.

Friction: the force that comes into play when an object moves or tries to move over another surface; it always acts opposite to the motion and is greater on rough surfaces.

Non-contact forces: act even without contact — magnetic force (between magnets/magnetic materials), electrostatic force (between charged bodies) and gravitational force (Earth’s pull, always attractive).

Weight: the force with which the Earth pulls an object towards itself; measured in newton (N) with a spring balance. Mass is the amount of matter (in g or kg) and stays the same everywhere, but weight can change from place to place.

Buoyant force (upthrust): the upward force a liquid applies on an object. If gravity > buoyant force the object sinks; if the two are equal it floats.

“Probe and ponder” & In-text Questions — Answers

Why does it feel harder to pedal a bicycle when going uphill than on flat ground?

ANSWERWhile going uphill, the Earth’s gravitational force pulls the bicycle and rider downwards along the slope, opposing the upward motion. The cyclist must apply an extra muscular force through the pedals to overcome this pull (and friction), so pedalling feels harder. On flat ground there is no such downhill pull to fight against.

Why is it easier to slip on a wet surface?

ANSWERFriction between our feet and the ground stops us from slipping. A film of water fills the tiny irregularities of the surface and keeps the surfaces apart, so the friction available to grip the floor is greatly reduced. With less friction to hold the foot in place, we slip easily.

Why do we feel ‘light’ or like we are ‘floating’ just after our swing reaches its highest point and begins to come down?

ANSWERAt the top of the swing, the swing and our body begin to fall back under gravity, both moving downward together. Because the seat is no longer pushing up against us as firmly as before, the support (push) on the body is reduced for a moment, giving the floating, light feeling we notice as the swing starts coming down.

Activity 5.1 (Let us explore): Did you move the box in any other way than shown in Fig. 5.1?

ANSWERA box can be moved by pushing it, pulling it (with hands or a rope), lifting and carrying it, sliding or rolling it, or tilting and dragging one edge. In every case we apply a push or a pull — that is, a force — to move the box.

Activity 5.2 (Let us analyse): Does a force cause a moving object to stop? Can it change speed, or direction of motion, or change the shape of an object?

ANSWER Yes. A force can stop a moving object (a friend holding a moving bicycle from behind — a pull) or decrease its speed. A force can change the direction of motion (hitting a moving ball with a bat — a push) and change the speed of a moving object. A force can also change the shape of an object (pressing an inflated balloon — a push). So a force can cause some or all of these effects.

Activity 5.3 (Let us investigate): When you gently push the object, does it stop after travelling some distance? Is there a force acting on it which brings it to rest? Does it stop again when pushed in the opposite direction?

ANSWERYes, the object slides a short distance and stops. A force acts between the surfaces in contact, in the direction opposite to the motion, and brings the object to rest. This force is friction. When pushed in the opposite direction the object again stops, because friction once more opposes the new direction of motion.

Activity 5.4 (Let us explore): Does the object stop at the same distance on all surfaces (glass, cloth, wood, ceramic tile, sand)?

ANSWERNo. The object stops after travelling different distances on different surfaces. This shows that friction depends on the nature of the surfaces in contact: it is greater on rough surfaces (like cloth and sand), so the object stops sooner, and smaller on smooth surfaces (like glass and tile), so it travels farther.

Activity 5.5 (Let us test): Does the second ring magnet stay floating? Do you feel a force when you push it down? Does it still float when the poles are reversed?

ANSWERWhen like poles face each other, the second magnet floats above the first because like poles repel. Pushing it down, we feel an upward force resisting us. If the poles are reversed so unlike poles face each other, they attract, and the magnet no longer floats. This proves a magnet exerts magnetic force on another magnet without touching it — a non-contact force.

Activity 5.6 (Let us experiment): On bringing the rubbed plastic scale/straw near small pieces of paper, do you notice something surprising? Why does it happen?

ANSWERThe paper pieces get pulled towards the scale/straw and stick to it. On rubbing, electrical (static) charges build up on the plastic, making it a charged object. A charged object exerts an electrostatic force on the uncharged paper pieces even without contact, pulling them towards it.

Activity 5.7 (Let us experiment): What do you observe when the two rubbed balloons are released, and when the woollen cloth is brought near a rubbed balloon? What do we infer?

ANSWER The two balloons move away from each other (they repel), while a balloon moves towards the woollen cloth (they attract). We infer that like charges repel and unlike charges attract. The balloons gained the same kind of charge (so they repel), while the balloon and the cloth gained opposite charges (so they attract). The two kinds of charge are called positive and negative.

Activity 5.8 (Let us observe): Take a ball and throw it vertically upwards. Does it come down? When thrown harder, does it still fall back?

ANSWERYes, in both cases the ball comes back down to the ground. The Earth attracts every object towards itself with the gravitational force (gravity). However high the ball is thrown, this downward pull brings it back, showing that gravity acts on all objects.

Activity 5.9 (Let us explore): When different objects are hung from a spring, is the stretch caused by each object the same?

ANSWERNo, the stretch is different for different objects. A heavier object stretches the spring more. This shows the Earth pulls different objects with different forces, i.e. their weights are different — so a spring can be used to measure weight.

Activity 5.10 (Let us observe): Looking at the spring balance in Fig. 5.13, what is the maximum weight it can measure?

ANSWERThe maximum weight it can measure is 10 N, so the scale has a range of 0 to 10 N.

Activity 5.11 (Let us calculate): Find the smallest value of weight the spring balance can measure (weight between two bigger marks = 1 N; 5 divisions between them).

ANSWER Weight difference between two bigger marks (e.g. 0 to 01 N) = 1 N. Number of small divisions between them = 5. Value of one small division = 1 N ÷ 5 = 0.2 N. So the smallest weight this spring balance can read is 0.2 N.

Activity 5.13 (Let us investigate): When you push an empty closed bottle into water, do you feel an upward push? Does it bounce up when released?

ANSWERYes. We feel an upward push, and on releasing it the bottle bounces back to the surface. This shows water applies an upward force, called upthrust or buoyant force, on the object. (All liquids apply such a force.)

Class 8 Science Curiosity Chapter 5 Solutions — Keep the curiosity alive

1. Match items in Column A with the items in Column B.

ANSWER
Column A (Type of force)Column B (Example)
(i) Muscular force(b) A child lifting a school bag
(ii) Magnetic force(e) A compass needle pointing North
(iii) Frictional force(a) A cricket ball stopping on its own just before touching the boundary line
(iv) Gravitational force(c) A fruit falling from a tree
(v) Electrostatic force(d) Balloon rubbed on woollen cloth attracting hair strands
So: (i)–(b), (ii)–(e), (iii)–(a), (iv)–(c), (v)–(d).

2. State whether the following statements are True or False. (i) A force is always required to change the speed of motion of an object.(ii) Due to friction, the speed of the ball rolling on a flat ground increases.(iii) There is no force between two charged objects placed at a small distance apart.

ANSWER (i) True. A change in speed cannot occur without the action of a force. (ii) False. Friction acts opposite to the motion, so it decreases the ball’s speed and finally stops it. (iii) False. Charged objects exert an electrostatic force (a non-contact force) on each other even when not touching.

3. Two balloons rubbed with a woollen cloth are brought near each other. What would happen and why?

ANSWER The two balloons move away from (repel) each other. Both balloons are rubbed with the same woollen cloth, so they acquire the same (like) kind of charge. Since like charges repel, the balloons push each other apart through the electrostatic force.

4. When you drop a coin in a glass of water, it sinks, but when you place a bigger wooden block in water, it floats. Explain.

ANSWER On every object in water two forces act: gravity (the object’s weight) downward and the buoyant force (upthrust) upward. For the coin, the downward gravitational force is greater than the buoyant force the water can provide, so the coin sinks. For the wooden block, the buoyant force becomes equal to its weight before it is fully submerged, so the upward and downward forces balance and the block floats. (Wood is less dense than water, so it displaces enough water to balance its weight.)

5. If a ball is thrown upwards, it slows down, stops momentarily, and then falls back to the ground. Name the forces acting on the ball and specify their directions. (i) During its upward motion(ii) During its downward motion(iii) At its topmost position

ANSWER In all three cases the main force is the Earth’s gravitational force (gravity), which always acts downwards (towards the Earth). (Air friction also acts, opposite to the ball’s motion.) (i) Upward motion: gravity acts downward, opposite to the motion, so the ball slows down. (ii) Downward motion: gravity acts downward, in the same direction as the motion, so the ball speeds up. (iii) Topmost position: gravity still acts downward, bringing the ball momentarily to rest and then pulling it back down.

6. A ball is released from the point P and moves along an inclined plane and then along a horizontal surface as shown in the Fig. 5.16. It comes to stop at the point A on the horizontal surface. Think of a way so that when the ball is released from the same point P, it stops (i) before the point A (ii) after crossing the point A.

ANSWER The ball stops because friction on the horizontal surface opposes its motion. Changing the friction changes where it stops. (i) To stop before A: increase the friction on the horizontal surface — for example, spread a rough material such as sand, cloth or a carpet on it. More friction stops the ball sooner. (ii) To stop after crossing A: reduce the friction — for example, make the surface smoother or polished (or place a glass/tile sheet). Less friction lets the ball travel farther before stopping.

7. Why do we sometimes slip on smooth surfaces like ice or polished floors? Explain.

ANSWERWalking depends on the friction between our feet and the ground gripping us in place. On ice or a polished floor the surface is very smooth, with very few irregularities to interlock, so the friction is very small. With too little friction to hold our feet, they slide forward and we slip.

8. Is any force being applied to an object in a non-uniform motion?

ANSWERYes. In non-uniform motion the object’s speed (or direction) keeps changing. A change in speed or direction cannot happen without a force, so a force must be acting on an object in non-uniform motion.

9. The weight of an object on the Moon becomes one-sixth of its weight on the Earth. What causes this change? Does the mass of the object also become one-sixth of its mass on the Earth?

ANSWER Weight is the gravitational force with which a body (Earth or Moon) pulls the object. The Moon’s gravitational pull is about one-sixth of the Earth’s, so the object’s weight on the Moon is about one-sixth of its weight on the Earth. No, the mass does not change. Mass is the amount of matter in the object; it stays the same everywhere — on the Earth, the Moon or any planet. Only the weight changes because gravity changes.

10. Three objects 1, 2, and 3 of the same size and shape but made of different materials are placed in the water. They dip to different depths as shown in Fig. 5.17. If the weights of the three objects 1, 2, and 3 are w1, w2, and w3, respectively, then (i) w1 = w2 = w3(ii) w1 > w2 > w3(iii) w2 > w3 > w1(iv) w3 > w1 > w2

ANSWER (iv) w3 > w1 > w2. Objects of the same size and shape displace more water as they sink deeper, so they feel a larger buoyant force only when heavier. The object that dips the deepest (3) is the heaviest, and the one that dips the least (2) is the lightest. From the depths shown in Fig. 5.17 (3 deepest, then 1, then 2 least), the order of weights is w3 > w1 > w2.

Common Misconceptions to Avoid

Watch out for these

  • Thinking a force needs only one object — a force always arises from the interaction of at least two objects.
  • Believing friction can speed up an object — friction always acts opposite to the motion, so it only slows objects down.
  • Treating weight and mass as the same — weight is a force (in N) that changes with gravity; mass (in g/kg) is the matter and stays constant.
  • Assuming gravity can repel — gravitational force is always attractive, unlike magnetic and electrostatic forces.
  • Confusing “non-contact” with “no force” — magnetic, electrostatic and gravitational forces act even without touching.
  • Saying smooth surfaces have no friction at all — they have less friction, not zero, which is why we still slip rather than glide forever.

Extra Practice Questions

Very Short Answer Type Questions

Q1. What is the SI unit of force?

ANSWERThe newton (symbol N).

Q2. Name one contact force and one non-contact force.

ANSWERContact force — friction (or muscular force); non-contact force — gravitational force (or magnetic/electrostatic force).

Q3. In which direction does friction always act?

ANSWEROpposite to the direction in which the object is moving or trying to move.

Short Answer Type Questions

Q1. Differentiate between contact and non-contact forces with one example each.

ANSWERContact forces act only when objects are in physical contact, e.g. friction. Non-contact forces can act from a distance without touching, e.g. gravitational force. Muscular force is a contact force; magnetic force is a non-contact force.

Q2. State four effects that a force can produce on an object.

ANSWERA force can (i) make an object move from rest, (ii) change its speed if it is moving, (iii) change its direction of motion, and (iv) change its shape. It may cause some or all of these effects.

Long Answer Type Question

Q1. Explain how a spring balance is used to measure the weight of an object, and why it reads weight in newton.

ANSWER A spring balance has a spring fixed at one end and a hook at the other, with a marked scale. When an object is hung from the hook, the Earth’s gravitational force pulls it down and stretches the spring. A heavier object stretches the spring more, so the amount of stretch indicates the pull, i.e. the weight. Since weight is a force, it is measured in the same unit as force — the newton (N). (A second scale often shows the corresponding mass in grams, calibrated for use on the Earth.)

MCQs & Assertion–Reason

1. The SI unit of force is the:

(a) kilogram    (b) newton    (c) joule    (d) watt

2. Which of the following is a non-contact force?

(a) muscular force    (b) friction    (c) gravitational force    (d) push of a hand

3. Friction always acts:

(a) in the direction of motion    (b) opposite to the motion    (c) upward    (d) downward

4. The force with which the Earth pulls an object towards itself is called its:

(a) mass    (b) weight    (c) friction    (d) upthrust

5. Which device is used to measure weight?

(a) thermometer    (b) beam balance    (c) spring balance    (d) measuring tape

6. Two like charges placed near each other will:

(a) attract    (b) repel    (c) stay still    (d) become neutral

7. Gravitational force is always:

(a) attractive    (b) repulsive    (c) zero    (d) sometimes attractive, sometimes repulsive

8. The upward force applied by a liquid on an object is called:

(a) friction    (b) muscular force    (c) buoyant force    (d) magnetic force

9. The smallest weight read by a spring balance with 1 N between big marks and 5 divisions between them is:

(a) 0.5 N    (b) 0.2 N    (c) 1 N    (d) 5 N

10. When an object is taken from the Earth to the Moon, its:

(a) mass increases    (b) weight stays the same    (c) mass stays the same but weight decreases    (d) both mass and weight become one-sixth

Answer key: 1-(b), 2-(c), 3-(b), 4-(b), 5-(c), 6-(b), 7-(a), 8-(c), 9-(b), 10-(c).

For each Assertion–Reason question, choose: (A) Both true and the Reason correctly explains the Assertion; (B) Both true but the Reason is not the correct explanation; (C) Assertion true, Reason false; (D) Assertion false, Reason true.

A-R 1. Assertion: Friction acts in a direction opposite to the motion of an object.

Reason: Friction arises due to the interlocking of irregularities on the two surfaces in contact.

A-R 2. Assertion: The weight of an object is different on the Earth and the Moon.

Reason: The mass of an object changes from the Earth to the Moon.

A-R 3. Assertion: Gravitational force is a non-contact force.

Reason: The Earth attracts objects towards itself even without touching them.

A-R 4. Assertion: Two unlike charges attract each other.

Reason: Like charges repel and unlike charges attract.

A-R 5. Assertion: A wooden block floats on water while a coin sinks.

Reason: The buoyant force balances the weight of the block but not that of the coin.

Answer key: 1-(A), 2-(C), 3-(A), 4-(A), 5-(A).

Quick Revision Summary

  • A force is a push or pull resulting from the interaction of two objects; its SI unit is the newton (N).
  • A force can change an object’s speed, direction of motion or shape, or make it move from rest.
  • Contact forces (act on touching): muscular force and friction; friction opposes motion and is greater on rough surfaces.
  • Non-contact forces (act from a distance): magnetic, gravitational and electrostatic forces.
  • The force exerted by a magnet is magnetic force; by a charged body, electrostatic force; by the Earth, gravitational force (always attractive).
  • Weight = the Earth’s pull on an object (in N), measured by a spring balance; mass (in g/kg) stays constant but weight can vary from place to place.
  • A liquid exerts an upward buoyant force (upthrust); if it equals the weight the object floats, if less the object sinks.

Real-life Applications

Forces are everywhere in daily life. Friction lets us walk, write and apply brakes, which is why tyres and shoe soles are made rough and roads are not too smooth. We reduce harmful friction with oil, grease and ball bearings, and streamline aeroplanes, ships and high-speed trains to cut down air and water friction. Gravity holds us and our belongings on the ground and brings thrown objects back down; the buoyant force lets ships and wooden boats float. Magnetic force runs compasses, fridge magnets and electric motors, while electrostatic force explains a comb attracting hair and dust sticking to a charged TV screen.

How to score full marks in this chapter

Learn the definition of force and the four effects it can produce, and clearly classify forces as contact (muscular, friction) or non-contact (magnetic, electrostatic, gravitational). Always state the direction of a force in answers (e.g. gravity acts downward, friction opposes motion). Practise the spring-balance least-count calculation (1 N ÷ 5 = 0.2 N) and never mix up weight (force, in N) with mass (matter, in kg).

Frequently Asked Questions

What is Class 8 Science Curiosity Chapter 5 about?

Chapter 5, Exploring Forces, is about force as a push or pull from the interaction of objects, its effects, contact forces (muscular force, friction), non-contact forces (magnetic, electrostatic, gravitational), weight and its measurement with a spring balance, and buoyant force (floating and sinking).

What is the difference between contact and non-contact forces?

Contact forces act only when two objects physically touch (e.g. friction and muscular force), while non-contact forces act even from a distance without touching (e.g. magnetic, electrostatic and gravitational forces).

How many questions are in the “Keep the curiosity alive” exercise of Chapter 5?

There are 10 questions, all solved step by step on this page along with the “Probe and ponder” prompts and the in-text activity questions.

Are these Class 8 Science Curiosity Chapter 5 solutions free?

Yes. All solutions are free and follow the official NCERT Curiosity textbook for 2026–27.

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