NCERT Solutions Class 8 Science Chapter 05 Exploring Forces

Question 1. Match items in Column A with the items in Column B.
Column A (Type of force)
(i) Muscular force
(ii) Magnetic force
(iii) Frictional force
(iv) Gravitational force
(v) Electrostatic force

Column B (Example)
(a) A cricket ball stopping on its own just before touching the boundary line
(b) A child lifting a school bag
(c) A fruit falling from a tree
(d) Balloon rubbed on woollen cloth attracting hair strands
(e) A compass needle pointing North
Answer: (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

In simple words: When you use your muscles to lift something, that is muscular force. When a magnet pulls things, that is magnetic force. When things slow down because surfaces rub together, that is friction. When things fall down, Earth is pulling them - that is gravity. When you rub a balloon on wool and it sticks to hair, that is electrostatic force.

Exam Tip: Match each force type to real-life examples you can see or feel. Remember that friction always opposes motion, and gravity always pulls downward toward Earth.

Question 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.
Answer: True. To make an object move faster or slower, a push or pull must act on it. Without a force, an object keeps moving at the same speed or stays at rest.
In simple words: Nothing changes speed by itself. You need a push or pull - that is, a force - to make it go faster or slower.

Exam Tip: This relates to Newton's first law of motion - remember that an object resists changes in motion unless a force acts on it.

Question 2. (ii) Due to friction, the speed of the ball rolling on a flat ground increases.
Answer: False. Friction works like a brake that slows things down. It always works against motion. So when a ball rolls, friction always makes it go slower, never faster.
In simple words: Friction stops moving things. It can never make something go faster.

Exam Tip: This is a trick question designed to test if you truly understand friction. Remember: friction always opposes the direction of motion.

Question 2. (iii) There is no force between two charged objects placed at a small distance apart.
Answer: False. Charged objects create an invisible force field around them. When two charged items come near each other, they either pull toward each other or push away from each other due to electrostatic force.
In simple words: Charged things can push or pull each other even without touching. This pushing or pulling is electrostatic force.

Exam Tip: Electrostatic force works without direct contact - this is a non-contact force like gravity and magnetism.

Question 3. Two balloons rubbed with a woollen cloth are brought near each other. What would happen and why?
Answer: When you rub two balloons with the same woollen cloth, both balloons collect the same type of static electrical charge. Similar electrical charges push away from each other. Just as two North poles of magnets push each other apart, two balloons with the same charge will repel each other and move apart.
In simple words: Both balloons get the same charge from the wool. Things with the same charge push each other away. So the balloons will move apart from each other.

Exam Tip: Remember the rule: like charges repel, unlike charges attract. This principle explains why the balloons push away.

Question 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: Two forces compete when an object is placed in water. First, gravity pulls the object downward with a force equal to its weight. Second, water pushes upward on the object with a buoyant force. For the coin, gravity pulls down harder than the water pushes up, so it sinks. For the wooden block, the upward push from water is strong enough to equal the downward pull of gravity. When these forces are balanced, the block floats.
In simple words: Gravity pulls objects down. Water pushes them up. If the water's push is strong enough to match gravity's pull, the object floats. If not, it sinks.

Exam Tip: Understand that buoyant force depends on how much water an object displaces. Heavier objects need to displace more water to float.

Question 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
Answer: During upward motion, two forces act on the ball. Gravitational force pulls the ball downward toward Earth. Air resistance (a form of friction from the air) also acts downward, opposing the upward movement of the ball.
In simple words: As the ball goes up, both gravity and air push it downward. This is why it slows down.

Exam Tip: Both forces point downward during upward motion - they work together to slow the ball.

Question 5. (ii) During its downward motion
Answer: During downward motion, gravitational force still pulls the ball downward toward Earth. Now air resistance acts upward, opposing the downward movement of the ball.
In simple words: Gravity pulls down, and air pushes up. Air pushes against the falling ball.

Exam Tip: The direction of air resistance changes - it always opposes motion, so it points upward when the ball falls.

Question 5. (iii) At its topmost position
Answer: At the highest point, the ball stops moving for just an instant. At this exact moment, only gravitational force acts on the ball, pulling it straight downward. Air resistance becomes zero because the ball is not moving at that instant.
In simple words: At the top, the ball does not move, so only gravity pulls on it. There is no air resistance because there is no motion.

Exam Tip: The instant the ball stops is the moment when velocity is zero and only gravity acts. After this instant, gravity pulls it downward again.

Question 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: Friction controls where the ball stops. The ball halts at point A because friction between the ball and the horizontal surface slows it down.

(i) To make the ball stop before point A, increase the friction on the surface. Lay a carpet or sandpaper on the horizontal surface to make it rougher. Greater roughness creates more friction, which stops the ball sooner.

(ii) To make the ball stop after crossing point A, decrease the friction on the surface. Polish the surface or apply a lubricant such as oil or talcum powder. A smoother, more slippery surface has less friction, allowing the ball to travel farther.
In simple words: Rough surfaces create more friction and stop the ball faster. Smooth surfaces create less friction and let the ball go farther.

Exam Tip: Understand that friction is directly related to surface texture - rougher surfaces produce stronger friction forces.

Question 7. Why do we sometimes slip on smooth surfaces like ice or polished floors? Explain.
Answer: Walking depends on friction between shoe soles and the ground. This friction gives our feet the grip needed to push off the ground. Ice and freshly polished floors are very smooth with almost no bumps or rough spots. With so little friction, our feet cannot get a firm grip. Without proper grip, our feet slide, and we slip.
In simple words: Our shoes grip the ground through friction. Smooth surfaces have no grip, so our feet slide.

Exam Tip: The lack of friction on smooth surfaces is the key reason for slipping - rough shoes or textured surfaces increase friction and prevent falls.

Question 8. Is any force being applied to an object in a non-uniform motion?
Answer: Yes. Non-uniform motion means the object's velocity is changing - it is speeding up, slowing down, or changing direction. Any change in velocity is called acceleration. To cause acceleration, a net (unbalanced) force must be applied. Therefore, an object in non-uniform motion always has a force acting on it.
In simple words: If something is changing speed or direction, a force must be pushing or pulling it. No force, no change.

Exam Tip: Remember that acceleration means any change in motion - speeding up, slowing down, or turning. Any acceleration requires a force.

Question 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 changes because of differences in gravitational pull. The Moon is smaller and has much less mass than Earth, so its gravity is weaker - about one-sixth as strong. Weight is the measure of gravitational pull, so an object weighs less on the Moon. Mass, however, does NOT change. Mass is the amount of material or matter an object contains. Whether you take a rock to the Moon, to Jupiter, or leave it on Earth, the amount of stuff it is made of stays the same. Mass remains constant everywhere in the universe.
In simple words: The Moon's weaker gravity makes things weigh less. But the things are still made of the same amount of stuff - their mass does not change.

Exam Tip: This is a critical distinction: weight depends on gravity (changes from place to place), but mass is the amount of material (stays the same everywhere).

Question 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: For an object to float, the buoyant force pushing upward must exactly match its weight pulling downward. The buoyant force equals the weight of water the object displaces. Object 1 floats high in the water, displacing only a small amount of water, so it must be lightest. Object 2 sits lower in the water than object 1 and must displace more water to stay afloat, making it heavier than object 1 (W₂ > W₁). Object 3 has sunk to the bottom, meaning its weight exceeds the maximum buoyant force water can provide, even when fully submerged, so it is the heaviest. The correct order is W₃ > W₂ > W₁.
In simple words: Things that float high are light. Things that sink lower in the water are heavier. Things at the bottom are the heaviest of all.

Exam Tip: Use the position of objects in water to rank their weights - floating high means light, floating low means heavier, sinking means heaviest. The depth tells you the weight order.