Test: Exploring Forces - Class 8 MCQ

Gravitational force is a non-contact force because it acts at a distance, pulling objects toward each other without any physical contact. This force is always attractive and is responsible for the weight of objects on Earth. An interesting fact is that gravitational force acts between all masses, not just those on Earth.

Kicking a ball is an example of a push force. When the foot strikes the ball, it applies a force in a specific direction, causing the ball to move. This demonstrates how force can initiate motion in an object.

Mass measures the amount of matter in an object and is constant regardless of location, while weight measures the gravitational force acting on that mass. Weight can change depending on the strength of the gravitational field, such as on different planets.

Buoyant force is the upward force exerted by a liquid on an object immersed in it. This force can determine whether an object floats or sinks depending on its weight relative to the buoyant force. An interesting fact is that objects with a density less than that of the liquid will float.

Archimedes' Principle explains why a ship floats on water. It states that an object immersed in a fluid experiences an upward buoyant force equal to the weight of the fluid displaced. If the weight of the ship is less than the weight of the water it displaces, it floats.

a) They are always unequal → Incorrect. Newton’s Third Law states that forces are equal in magnitude, though they act on different objects.

b) They have no effect on each other → Incorrect. The forces exist because of interaction, so they definitely affect the motion of the objects.

c) They cancel each other out → Incorrect. The forces don’t cancel because they act on different objects. For cancellation, forces must act on the same object.

d) They are equal and opposite → Correct. Whenever two objects interact, each exerts a force on the other that is equal in size and opposite in direction (Newton’s Third Law).

Friction is classified as a contact force because it arises from the interaction between two surfaces in contact. It acts to oppose the motion of an object sliding or attempting to slide over another surface, making it essential in various practical applications.

The weight of an object increases if it is taken to a planet with stronger gravitational force. Weight is directly proportional to the gravitational acceleration acting on the object. This is why astronauts weigh less on the Moon than on Earth, as the Moon's gravity is weaker.

• Muscular force: When you squeeze an object (like a rubber ball or clay), you apply pressure using your muscles. This muscular force changes its shape.
• Magnetic force: Acts only on magnetic materials and does not change the shape of an object when you squeeze it.
• Gravitational force: Pulls objects toward the Earth’s center. It doesn’t cause shape change during squeezing.
• Electrostatic force: Acts between charged objects. It is not responsible for squeezing shape change.

Rougher surfaces have more friction because the irregularities in the surfaces interlock more effectively, resisting motion. This is why objects slide more easily on smooth surfaces compared to rough ones. This concept is vital in engineering and design to reduce or increase friction as needed.

The SI unit of force is the newton (N). It is defined as the force required to accelerate a one-kilogram mass by one meter per second squared. This unit helps in quantifying force in scientific experiments and calculations.

A force is defined as a push or pull applied to an object. It is responsible for changing the state of motion of that object, including starting, stopping, or changing its direction. Understanding this fundamental concept is crucial in physics as it explains how objects interact with one another.

Gravitational force is not a contact force, as it acts at a distance. In contrast, friction, muscular force, and tension all require physical contact between objects. Understanding these distinctions is essential in physics for analyzing different types of interactions.

Like-charged objects repel each other when brought close together. This is a principle of electrostatics, where similar charges repel and opposite charges attract. This property is fundamental in understanding electrical interactions and applications.

An object's mass remains the same regardless of its location, whether on Earth, the Moon, or any other planet. Mass is a measure of the amount of matter in an object and does not change with gravitational influence.

Friction always acts in the opposite direction to the motion of an object, which means it will slow down the object. This resistance is due to the interactions between the surfaces in contact. For example, a box sliding on a rough surface will come to a stop quicker than on a smooth surface due to greater friction.

When an object experiences balanced forces, it will either remain at rest or continue moving at a constant speed. This is because the net force acting on the object is zero, meaning that the forces are equal in magnitude and opposite in direction, resulting in no change in motion.

Applying a push force to a stationary object will cause it to start moving. This is an example of how force can change the state of an object from rest to motion. This principle is foundational in physics, as it demonstrates the relationship between force and motion.

The speed of an object thrown upwards against gravity decreases until it comes to a stop at its highest point. Gravity acts as a downward force, continuously opposing the upward motion until the object halts and begins to fall back down.

Applying brakes to a moving vehicle decreases its speed or stops it entirely. This action involves a push force that counteracts the vehicle's motion, illustrating how force can control the movement of objects.