Exploring Forces Class 8 Science Curiosity Chapter 5 Keep the
curiosity alive
1. Match items in Column A with the items in
Column B.
📊 Given:
|
Column A (Type of force) |
Column B (Example) |
|
(i) Muscular force |
(a) A cricket ball stopping on its own just before
touching the boundary line |
|
(ii) Magnetic force |
(b) A child lifting a school bag |
|
(iii) Frictional force |
(c) A fruit falling from a tree |
|
(iv) Gravitational force |
(d) Balloon rubbed on woollen cloth attracting hair
strands |
|
(v) Electrostatic force |
(e) A compass needle pointing North |
✅ See
Answer (with reasoning):
🟢 (a) A
cricket ball stopping on its own just before touching the boundary line
➡️ (iii)
Frictional force
💡
Explanation:
👉 Grass creates friction
🛑 which
opposes motion and slows the ball down
🟢 (b) A
child lifting a school bag
➡️ (i)
Muscular force
💡
Explanation:
👉 Muscles 💪 apply force to lift the
bag against gravity
🟢 (c) A
fruit falling from a tree
➡️ (iv)
Gravitational force
💡
Explanation:
👉 Earth pulls objects
towards itself 🌍 → Gravity
🟢 (d)
Balloon rubbed on woollen cloth attracting hair strands
➡️ (v)
Electrostatic force
💡
Explanation:
👉 Rubbing creates static
charge ⚡ →
attracts hair
🟢 (e) A
compass needle pointing North
➡️ (ii)
Magnetic force
💡
Explanation:
👉 Earth acts like a giant
magnet 🧲 →
compass aligns North
📊 ✅ Final Matching Table
|
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 🛑 |
|
(iv) Gravitational force |
(c) A fruit falling 🍎 |
|
(v) Electrostatic force |
(d) Balloon attracting hair ⚡ |
🎯 Quick
Revision Trick 🧠
👉 Muscle
→ Lift 💪
👉 Magnet →
Compass 🧲
👉 Friction → Stop 🛑
👉 Gravity → Fall 🌍
👉 Static →
Attraction ⚡
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.
👉 See
Answer: True ✅
💡
Explanation:
➡️ An object will keep moving at
a constant speed 🚶♂️ (or
stay at rest 🛑)
unless a net force acts on it
➡️ To make something speed up
or slow down, a push or pull is needed
🔴 (ii)
Due to friction, the speed of the ball rolling on a flat ground increases.
👉 See
Answer: False ❌
💡
Explanation:
➡️ This is a tricky question 😏
➡️ Friction acts like a brake 🛑
➡️ It always opposes motion,
so it reduces speed, not increases
🔴 (iii)
There is no force between two charged objects placed at a small distance apart.
👉 See
Answer: False ❌
💡
Explanation:
➡️ Charged objects create an electric
field ⚡
➡️ When they come close:
✔️ They either attract 🤝
✔️ Or repel 🚫
➡️ This is called Electrostatic
Force
⚡ 3. Two
balloons rubbed with a woollen cloth are brought near each other. What would
happen and why?
👉 See
Answer:
🎈 When
both balloons are rubbed with the same woollen cloth:
➡️ They get the same type of
electric charge ⚡
💡 Think
like this:
👉 Same team jersey 👕 = same charge
👉 Same charges → repel
each other 🚫
📌 Just
like:
🧲 Magnet (North–North /
South–South) → repel
➡️
Therefore:
🎈🎈 The
two balloons will move apart (repel) due to electrostatic force ⚡
🎯 Quick
Revision Trick 🧠
👉 Force
changes motion 🔄
👉 Friction slows down 🛑
👉 Same charges repel ⚡
⚖️ 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.
👉 See
Answer:
💡 This
is a battle between two forces ⚔️
🔽 1.
Gravitational Force (Weight)
➡️ Pulls
objects downwards 🌍
🔼 2.
Buoyant Force (Upthrust)
➡️ Water
pushes objects upwards 💧
🪙 Coin
Case:
➡️
Gravity (↓) > Buoyant force (↑)
👉 Coin sinks ⬇️
🪵 Wooden
Block Case:
➡️
Buoyant force (↑) ≥ Gravity (↓)
👉 Block floats ⬆️
🎯 Conclusion:
👉 Object floats when upward
force balances or exceeds downward force
👉 Object sinks when gravity
is stronger
🎾 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
👉 See
Answer:
💡 Two
forces act on the ball:
➡️ 🌍 Gravitational Force
→
Downward ⬇️
➡️ 🌬️ Air Resistance (Friction) →
Downward ⬇️
📌 Both
forces oppose upward motion → ball slows down
🔽 (ii)
During its downward motion
👉 See
Answer:
💡 Again
two forces act:
➡️ 🌍 Gravitational Force
→
Downward ⬇️
➡️ 🌬️ Air Resistance → Upward
⬆️
📌 Air
resistance now opposes falling motion
⏸️ (iii)
At its topmost position
👉 See
Answer:
💡 At
this instant:
➡️ 🌍 Only Gravitational
Force acts downward ⬇️
➡️ 🌬️ Air resistance = zero (because
velocity = 0)
📌 Ball
stops for a moment before falling
🎯 Quick
Revision Trick 🧠
👉 Sink =
Gravity > Buoyant 💧
👉 Float = Forces balanced
⚖️
👉 Upward motion → both
forces ↓
👉 Downward motion → air ↑,
gravity ↓
Question 6, 7 and 8 in Class 8 Curiosity Chapter
5
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.
See Answer This is all about controlling friction! The ball
stops at point A because of the friction between the ball and the horizontal
surface.
(i) To make the ball stop before point A, we need to increase the friction. We
could make the horizontal surface rougher, for example, by laying a piece of
carpet or sandpaper on it.
(ii) To make the ball stop after crossing point A, we need to decrease the
friction. We could make the horizontal surface smoother. Polishing the surface
or applying a lubricant like a little bit of oil or talcum powder would reduce
friction and allow the ball to travel farther.
7. Why do we sometimes slip on smooth surfaces like ice or
polished floors? Explain.
See Answer We can walk because of the friction between the soles of our shoes
and the ground. This friction provides the grip we need to push off the ground.
Smooth surfaces like ice or a freshly polished floor have very few bumps and
irregularities. This means there is very little friction. Without that
essential grip, our feet slide easily, causing us to slip.
8. Is any force being applied to an object in a non-uniform
motion?
See Answer Yes. Non-uniform motion means the object’s velocity is changing—it’s
either speeding up, slowing down, or changing direction. Any change in velocity
is called acceleration, and to make an object accelerate, you must apply a net
(unbalanced) force. So, if you see an object in non-uniform motion, you can be
sure a force is at work.
Class 8 Science Curiosity Chapter 5 Question 9
and 10
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?
See Answer This is a key difference between mass and weight!
The change in weight is caused by the difference in gravity. The Moon is much
smaller and has less mass than the Earth, so its gravitational pull is much
weaker—about one-sixth as strong. Since weight is just the measure of this
gravitational pull, the object’s weight is less on the Moon.
However, the mass of the object does NOT change. Mass is the amount of ‘stuff’
or matter an object is made of. Whether you take a rock to the Moon, to
Jupiter, or keep it on Earth, it’s still made of the same amount of stuff. So,
its mass remains constant everywhere.
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
See Answer This is a brilliant puzzle about floating and
sinking. Let’s analyze the clues from the picture.
For an object to float, the upward buoyant force must exactly balance its
downward weight. The buoyant force is equal to the weight of the water the
object pushes aside (displaces).
– Object 1 is floating very high, which means it displaces only a small amount
of water. Therefore, it must be the lightest.
– Object 2 is floating lower in the water than object 1. It has to displace
more water to stay afloat, which means it must be heavier than object 1. So, W₂ > W₁.
– Object 3 has sunk to the bottom. This means its weight (W₃) is greater than the maximum
possible buoyant force the water can provide, even when the object is
completely underwater.
From this, we know for certain that the sunken object (3) is the heaviest, and
between the two floating objects, object 2 is heavier than object 1.
So the correct order of weights is W₃ > W₂ > W₁.
It appears that none of the multiple-choice options provided in the book match
this correct conclusion. This can sometimes happen in textbooks! The most
important thing is to understand the scientific principle, which clearly tells
us the correct order is W₃ > W₂ > W₁.
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