All questions of Exploring Forces for Class 8 Exam

Understanding Contact Forces
In physics, forces can be classified into two main types: contact forces and non-contact forces. Contact forces occur when objects physically touch each other, while non-contact forces act at a distance without physical contact.
Contact Forces Explained
- Tension: This is a force transmitted through a string, rope, or wire when it is pulled tight by forces acting from opposite ends. It is a classic example of a contact force.
- Friction: This force opposes the motion of an object when it is in contact with another surface. It arises from the interaction between the surfaces and is therefore a contact force.
- Muscular Force: This is the force exerted by muscles when they contract. When a person pushes or pulls an object, this force is applied through direct contact, making it a contact force.
Gravitational Force as a Non-Contact Force
- Gravitational Force: Unlike the others, gravitational force acts at a distance. It is the attraction between two masses, such as the Earth and an object. This force does not require physical contact to exist; it operates through the gravitational field.
Conclusion
In summary, the correct answer to the question is option 'C', the gravitational force, as it is a non-contact force, while the others—tension, friction, and muscular force—are all contact forces that require direct interaction between objects. Understanding these distinctions is fundamental in the study of physics and mechanics.

Understanding Non-Contact Forces
Non-contact forces are those that can act on an object without direct physical contact. In this case, the correct answer is option 'B', the gravitational force.
What is Gravitational Force?
- Gravitational force is the attraction between two masses.
- It acts at a distance, pulling objects toward each other, like the Earth pulling us towards its center.
Examples of Non-Contact Forces
- Gravitational Force: As mentioned, it operates without any physical contact, affecting everything with mass.
- Magnetic Force: Attracts or repels magnetic materials without direct contact.
- Electrostatic Force: Acts between charged particles, attracting or repelling them from a distance.
Contact Forces vs. Non-Contact Forces
- Contact Forces: Require physical touch to act on an object.
- Muscular Force: Generated by muscle contraction and requires direct physical contact.
- Tension: The force transmitted through a string, rope, or cable when it is pulled tight.
- Friction: The resistance that one surface or object encounters when moving over another.
Why Gravitational Force is Unique
- Unlike muscular force, tension, or friction, gravitational force can influence objects across vast distances (like the Moon influencing ocean tides on Earth).
- It is a fundamental force of nature, essential for the structure of the universe.
Understanding these concepts helps in grasping the fundamental differences between forces acting at a distance and those requiring contact.

Understanding Why a Ship Floats
The principle that explains why a ship floats on water is known as Archimedes' Principle. This principle provides insight into how buoyancy works.
What is Archimedes' Principle?
- Archimedes' Principle states that any object submerged in a fluid experiences an upward force, known as buoyant force, that is equal to the weight of the fluid displaced by the object.
Why Ships Float?
- Weight vs. Buoyant Force: A ship floats because the weight of the water it displaces is greater than or equal to the weight of the ship itself. If the weight of the displaced water is less than the weight of the ship, the ship will sink.
- Shape and Design: Ships are designed with a hull shape that maximizes the volume of water displaced. This allows large vessels to float even though they may be heavy.
Factors Affecting Buoyancy
- Density: The density of the ship must be less than the density of water for it to float. Ships are constructed using materials that are lighter than water when accounting for their shape.
- Surface Area: A larger surface area can help distribute the weight of the ship over a greater volume of water, enhancing buoyancy.
Conclusion
In summary, Archimedes' Principle clarifies that a ship floats because of the balance between the weight of the ship and the buoyant force acting on it from the water below. This principle is fundamental in understanding buoyancy and the mechanics of floating objects.

Understanding Interaction Forces
When two objects interact, they exert forces on each other that are governed by Newton's Third Law of Motion. This law states that for every action, there is an equal and opposite reaction.
Key Concepts:

• Equal and Opposite Forces: When Object A exerts a force on Object B, Object B simultaneously exerts a force of equal magnitude but in the opposite direction back on Object A.
• Real-World Examples:
  
  • When you push a wall, the wall pushes back with an equal force.
  • In a rocket launch, the rocket engines push down on the ground, and the ground pushes back up with an equal force, propelling the rocket upwards.
  
  
• Why They Don't Cancel Out: While the forces are equal and opposite, they act on different objects. Therefore, they do not cancel each other out in a way that affects the motion of a single object.
• Importance in Physics: Understanding these forces is vital for analyzing interactions in various fields, including engineering, sports, and mechanics.

Conclusion:
The forces exerted by two interacting objects are always equal in magnitude and opposite in direction, as per Newton's Third Law. This fundamental principle helps explain a wide range of physical phenomena and is crucial for understanding motion and forces in our world.

Understanding Mass and Weight
Mass and weight are fundamental concepts in physics, often confused but distinctly different in nature.
Definition of Mass
- Mass is a measure of the amount of matter in an object.
- It is a scalar quantity, meaning it has magnitude but no direction.
- Mass is constant regardless of location; it remains the same whether you are on Earth, the Moon, or in space.
Definition of Weight
- Weight is the force exerted by gravity on an object.
- It is a vector quantity, meaning it has both magnitude and direction (towards the center of the Earth).
- Weight can change depending on the gravitational field strength. For example, an object weighs less on the Moon than on Earth due to weaker gravity.
Relationship Between Mass and Weight
- The relationship is expressed by the equation: Weight = Mass × Gravitational Acceleration (W = m × g).
- While mass is a measure of how much matter is in an object, weight measures the gravitational force acting on that mass.
Inertia and Gravitational Force
- Mass measures inertia, which is an object's resistance to changes in its state of motion. A larger mass means greater inertia.
- Weight measures how strongly gravity pulls down on that mass. This is why weight varies with gravity, while mass does not.
In summary, mass and weight are related but represent different physical properties. Understanding this distinction is crucial for grasping basic principles of physics.

Understanding Mass and Weight
When discussing the movement of an object from Earth to the Moon, it's essential to differentiate between mass and weight.
Mass vs. Weight
- Mass is the amount of matter in an object and is a scalar quantity, which means it does not change regardless of location.
- Weight, however, is the force exerted on an object due to gravity and varies depending on the gravitational pull of the celestial body.
Mass on Earth vs. Moon
- An object retains the same mass whether it is on Earth or on the Moon. For instance, if an object has a mass of 10 kg on Earth, it will also have a mass of 10 kg on the Moon.
Why Does Mass Remain the Same?
- Mass is intrinsic to the object; it is a fundamental property.
- The gravitational force acting on the object changes when moving from Earth (with a gravitational acceleration of about 9.81 m/s²) to the Moon (with a gravitational acceleration of about 1.62 m/s²), but the mass itself does not change.
Conclusion
Thus, the correct answer to what happens to an object's mass when moved from Earth to the Moon is option 'C': it remains the same. Understanding this distinction helps clarify many concepts in physics, particularly in discussions regarding weightlessness and space travel.

Understanding Weight and Gravity
When an object is taken to a planet with a stronger gravitational force, its weight changes due to the influence of gravity. Weight is defined as the force exerted on an object due to gravity, and it is calculated by the equation:
Weight = Mass × Gravitational Acceleration
Implications of Stronger Gravity
- Increased Gravity: A planet with a stronger gravitational force exerts more pull on objects. This means that for the same mass, the weight of the object will increase.
- Example: If you weigh 60 kg on Earth and travel to a planet with double the gravitational pull, your weight would effectively double as well.
Why Weight Increases
- Mass Remains Constant: The mass of the object does not change when moving from one planet to another. It is the gravitational acceleration that changes.
- Direct Relationship: The relationship between weight and gravitational force is direct; as gravity increases, weight increases proportionally.
Conclusion
In summary, when an object is taken to a planet with stronger gravitational force, its weight increases. This is because the gravitational pull on the object is stronger, making it heavier than it would be on a planet with weaker gravity. Thus, the correct answer is option 'D': it increases.

The Concept of Balanced Forces
When an object experiences balanced forces, it means that the total force acting on it is zero. This balance leads to specific outcomes regarding the object's motion.
What Are Balanced Forces?
- Balanced forces occur when two or more forces acting on an object are equal in size but opposite in direction.
- They cancel each other out, resulting in no net force.
Consequences of Balanced Forces
- Remains at Rest: If the object is stationary, it will stay at rest. For example, a book on a table remains in place as the gravitational force downward is balanced by the normal force upward.
- Continues Moving at Constant Speed: If the object is already in motion, it will continue to move at the same speed in the same direction. A car cruising at a steady speed on a straight road is a perfect illustration-here, the engine's forward force is balanced by friction and air resistance.
Summary of Option B
- The correct answer is option 'B' because balanced forces do not change the state of motion of an object.
- It will either remain at rest or keep moving uniformly, demonstrating Newton's First Law of Motion, which states that an object in a state of rest or uniform motion will stay that way unless acted upon by an unbalanced force.
Understanding balanced forces is crucial in physics as it lays the foundation for analyzing more complex motion scenarios.

Understanding the Motion of an Object Thrown Upwards
When an object is thrown upwards against the force of gravity, it experiences a change in speed due to gravitational pull. Let's explore why option 'B' is the correct answer.
Initial Speed and Upward Motion
- When you throw an object upward, it starts with an initial speed.
- This speed is determined by the force applied during the throw.
Effect of Gravity
- Gravity constantly acts downward on the object.
- This force opposes the upward motion, causing the object to slow down.
Decrease in Speed
- As the object ascends, its speed decreases gradually because of gravitational pull.
- The upward velocity diminishes until it reaches a point where it becomes zero.
Point of Stopping
- At the peak of its trajectory, the object's speed is zero for just an instant before it starts descending.
- This point is crucial; it marks the transition from upward motion to downward motion.
Conclusion
- Therefore, as the object is thrown upwards, its speed decreases until it stops.
- This is why option 'B' is correct: the speed decreases until it stops before reversing direction due to gravity.
Understanding these concepts of motion helps clarify why objects behave the way they do when thrown against gravitational forces.