NCERT Solutions for Class 8 Science Chapter 5 – Exploring Forces

The NCERT Solutions for Class-08 Science Chapter-05 - Exploring Forces provide students with an opportunity to learn about the difference between types of forces and how they affect motion, shape and direction of objects through a variety of practical examples that relate to everyday life, e.g. the activity of pushing and pulling, as well as the concepts of friction and gravity.

Chapter 05 assists students in developing their conceptual understanding of the relationship between science and their real-world experiences, including ways that the action (force) of pushing or pulling can affect an item's shape and whether it moves forward, or stays in place; and how gravity can cause something to fall, or remain on the ground.

Each solution has been broken down into easy-to-understand steps. This gives students the best opportunity to learn all about the effect of forces on the motion and interaction of things in their environment.

1.0NCERT Solutions for Class 8 Science Chapter 5 PDF Download

During your studies, the NCERT Solutions for Class 8 Science - Exploring Forces PDF provides students with easy access to all of the solutions provided by ALLEN’s faculty for convenient review.

Through careful preparation and expertise, we have ensured that our solutions are accurate, clear and provide students with a thorough understanding of all material contained in the syllabus. Additionally, the suggested solutions assist students in effectively reviewing their respective topics and gaining confidence in their ability to be successful on exams.

2.0NCERT Questions with Solutions Class 8 Science Chapter 5 Detailed Solutions

1. Match the items in Column-I with the items in Column-II.

Solution:
(A → q), (B → t), (C → p), (D → r), (E → s)

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.

Solution
(i) True
A force is always required to change the speed of motion of an object.

(ii) False
Due to friction, the speed of the ball rolling on a flat ground decrease.

(iii) False
Electrostatic force acts between charged objects – they may attract or repel.

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

Solution
When two balloons are rubbed with a woollen cloth and then brought near each other, they will repel each other. This happens because rubbing transfers electrons from the wool to the balloons, making both balloons negatively charged. Since like charges repel each other, the two balloons push away from one another.

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.

Solution

It's all about being heavy for your size. A coin is very heavy for its small size. It's so heavy that the water can't hold it up, so it sinks. The wooden block is very light for its big size. Because it's so spread out and light, the water can easily hold it up, so it floats.

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.

Solution

(i) During its upward motion:
Force of gravity acts downwards and air resistance (friction) acts downwards to oppose the upward motion.

(ii) During its downward motion:
Force of gravity still acts downwards and air resistance (friction) acts upwards to oppose the downward motion.

(iii) At its topmost position:
The velocity of the ball is zero for a moment so, air resistance is zero but the force of gravity still acts downwards, pulling it back toward Earth.

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 Figure. 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.

Solution
When the ball rolls down from point P, it gets some energy and keeps moving forward on the flat surface until friction (the rubbing force between the ball and the ground) makes it stop at point A.

(i) To make the ball stop before A,
We need to increase friction.
For example, put sand, rough cloth, or make the floor rough. Then the ball will lose energy faster and stop earlier, before A.

(ii) To make the ball stop after crossing A,
We need to reduce friction.
For example, polish the floor, put oil, or make it smooth. Then the ball will keep rolling longer and stop after A.

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

Solution- We slip on smooth surfaces due to a lack of friction, which is the gripping force between your shoes and the ground. When you walk, your feet push backward, and friction pushes you forward. Smooth surfaces like polished floors or ice have very few microscopic bumps for your shoes to grip thus reduces friction causing you to slip.

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

Solution - Yes, a force is definitely being applied. Non-uniform motion means an object is either speeding up, slowing down, or changing direction. Think of a car: to go faster, you press the gas pedal (applying more force). To slow down, you hit the brakes (applying a braking force). To turn, you use the steering wheel to apply a force that changes the car's direction. So, any change from moving at a steady speed in a straight line requires a force.

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?

Solution - This change is caused by a difference in gravity. The Moon is much smaller than the Earth, so its gravitational pull is far weaker—only about one-sixth as strong. Since weight is the measure of gravity's pull on an object, your weight on the Moon becomes one-sixth of what it is on Earth. No, the mass of the object does not change. Mass is the amount of matter, or "stuff," in an object, and that amount stays the same 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 Figure. 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

Solution - The correct answer is (ii) w₁ > w₂ > w₃.

For any object to float, the water has to push it up with a force that exactly equals the object's own weight. This upward push, called buoyant force, is equal to the weight of the water that the object pushes out of its way. 

Object 1 sinks the deepest, meaning it has to push aside the most water to float. This means it needs the biggest upward push from the water, so it must be the heaviest (w₁). Object 3 displaces the least water, so it's the lightest (w₃).

3.0Quick Insights About the Chapter – Exploring Forces

• Oppositional Force: Any two charged objects, such as two balloons each created with wool(rubbing with wool), will generate forces opposing each other's motions during repulsion.
• Role of the Friction: Friction must work against the external surface in order for someone or something to walk. The friction created by your foot's and shoe's movement against the ground generates force opposing the upward motion.
• A Momentary Change to Rest: When a ball is thrown into the air and reaches its highest point, its air resistance will momentarily halt its motion, but air resistance will be zero at the apex of upward motion.
• Contributing Density: A wooden block floats because it is very lightweight compared to its height and width due to the density factor.
• Varying Weights: The weight of an object can vary based on where in the universe you find that object, due to the force of gravity being variable based on the gravitational pull of that area or planet.

4.0Benefits of Studying This Chapter – Exploring Forces

• Practical Safety: Explains why we slip on smooth surfaces like ice (lack of friction) and how to manage friction for safety.
• Understanding Earth and Space: Provides the scientific basis for why weight changes on the Moon (one-sixth of Earth's weight) while mass remains constant.
• Mechanical Insight: Teaches how to control motion by increasing or decreasing friction, such as using sand to stop a rolling ball or oil to help it roll further.
• Physics Foundation: Establishes the relationship between electrostatic charges, magnetic fields, and physical movement that is essential for higher-level science.