All questions of Force and Pressure for Class 8 Exam

If we push or pull any object we use force to push or pull it. So... Force is both push and pull.

The correct answer is option 'C' - Magnitude.

Force is a physical quantity that is used to describe the interaction between objects. It can cause objects to accelerate, decelerate, or change direction. The strength of force is expressed by its magnitude, which refers to the size or quantity of the force.

Here's a detailed explanation of the other options and why they are not the correct answers:

a) Weight:
Weight is the force experienced by an object due to gravity. It is the measure of the gravitational force acting on an object's mass. While weight is a measure of force, it is not the same as the strength of force. Weight depends on the mass and the acceleration due to gravity, but the strength of force is a more general term that can encompass other types of forces beyond gravity.

b) Mass:
Mass is a measure of the amount of matter in an object. It is a scalar quantity and is not directly related to the strength of force. However, the mass of an object does affect the force required to accelerate it. According to Newton's second law of motion, the force acting on an object is equal to the mass of the object multiplied by its acceleration. So while mass is not the strength of force, it is related to the force required to produce a certain acceleration.

d) Longitudinal force:
Longitudinal force refers to a force that acts in the same direction as an object's motion. It is a type of force that can cause objects to accelerate or decelerate. However, it is not a measure of the strength of force in general. The magnitude of a longitudinal force would be a measure of its strength, but the term "longitudinal force" itself does not inherently imply the strength of force.

In conclusion, the strength of force is expressed by its magnitude, which refers to the size or quantity of the force. Other factors such as weight, mass, and the direction of force are related to force but do not directly measure its strength.

**False**

Friction is a type of force that opposes the relative motion between two surfaces in contact. It acts parallel to the surface and opposes the motion or tendency of motion between the surfaces. Therefore, friction is an example of a contact force, not a non-contact force.

Friction can occur between solid surfaces, such as when you try to slide a heavy box across the floor. It can also occur between a solid and a fluid, such as air resistance when an object moves through the air. In both cases, the surfaces must be in contact for friction to occur.

**Contact Forces vs Non-Contact Forces:**

Contact forces are those forces that require direct contact between two objects or substances for them to occur. Examples of contact forces include friction, normal force, tension force, and applied force. These forces are exerted through physical contact between the objects involved.

On the other hand, non-contact forces are forces that act on an object without any direct physical contact. These forces can act over a distance and do not require any physical contact between the objects involved. Examples of non-contact forces include gravitational force, magnetic force, and electrostatic force.

**Explanation:**

Friction is a contact force because it requires the surfaces of two objects to be in contact in order to occur. When two surfaces are in contact, the microscopic irregularities on the surfaces interact with each other, causing resistance to motion. This resistance is what we experience as friction.

For example, if you try to slide a heavy box across the floor, the roughness of the floor and the box's surface interact, creating friction that opposes the motion. If there was no contact between the box and the floor, there would be no friction and the box would easily slide without any resistance.

Therefore, since friction requires contact between surfaces to occur, it is not an example of a non-contact force but rather a contact force.

Force is the push or pull activity on an object. It has the following properties : 1) Force can change the direction of a moving object. For example, we can change the direction of a moving ball by kicking it in another direction. 2) Force can change the shape of an object. For example, we can change the shape of a paper by crumbling it. 3) Force can change the speed by making a moving object move faster. For example, we can change the speed of a ball by kicking it. 4) Force can stop or slow down a moving object. For example, we can catch a falling ball and can thus stop it from falling. 5) Force can move an object in rest. For example, we can move a chair by pulling it.

Explanation:
The statement is False.
When two forces act in opposite directions on an object, the net force is determined by the sum of the magnitudes of the two forces. The net force is not the difference between the two forces.
Here's a detailed explanation:
1. Definition of net force: Net force is the vector sum of all the individual forces acting on an object. It describes the overall effect of all the forces combined.
2. Opposite forces: When two forces act in opposite directions, they cancel each other out to some extent.
3. Equal magnitude opposite forces: If the two forces have equal magnitudes, they will completely cancel each other out, resulting in a net force of zero. The object will remain at rest or continue with its constant velocity.
4. Unequal magnitude opposite forces: If the two forces have different magnitudes, the resulting net force will be in the direction of the larger force. The net force will be equal to the difference between the magnitudes of the two forces.
5. Example: Let's consider an object with a force of 10 N acting to the right and a force of 5 N acting to the left. The net force will be 10 N - 5 N = 5 N to the right.
In summary, the net force is determined by summing the magnitudes of the individual forces, not by taking the difference between them.

The tendency of an object to maintain its state of motion, to remain at rest or to keep moving at a constant velocity, is known as inertia.

Pressure Exerted by Sharp Needle vs. Blunt Needle

Pressure is defined as the force applied per unit area. When comparing the pressure exerted by a sharp needle and a blunt needle on a surface, the key factor to consider is the surface area in contact with the object.

Sharp Needle
- A sharp needle has a very small surface area in contact with the object.
- As the surface area is small, the force applied by the sharp needle is concentrated over a small area.
- This results in a higher pressure being exerted by the sharp needle on the surface.

Blunt Needle
- A blunt needle has a larger surface area in contact with the object.
- The force applied by the blunt needle is distributed over a larger area.
- Due to the larger surface area, the pressure exerted by the blunt needle on the surface is lower compared to that of a sharp needle.

Therefore, the pressure exerted by a sharp needle is more than the pressure exerted by a blunt needle. This is because the force is concentrated over a smaller area in the case of a sharp needle, resulting in higher pressure.

Option B,C,d
D are examples of friction force which is a contact force wherein Option A is an example of magnetic force which is a non- contact force .

Understanding Net Force
When discussing forces acting on an object, the net force is the vector sum of all the forces. This means that when forces are applied, they can either combine or cancel each other out, leading to different effects on the object's motion.
Conditions for Zero Net Force
For the net force on an object to be zero, the forces acting upon it must be balanced. Here are the conditions:

• Opposite Directions: When two forces act on an object in opposite directions and are equal in magnitude, they cancel each other out. For example, if one force pulls an object to the right with 5 N and another pulls it to the left with 5 N, the net force is zero.
• Same Direction: If two forces act on an object in the same direction, they add up rather than cancel each other. For instance, two forces of 3 N and 2 N acting to the right result in a net force of 5 N to the right.
• Sometimes Opposite and Sometimes in Same Direction: If forces alternate between being in the same and opposite directions, the net force can still change depending on their magnitudes and directions. Thus, it does not guarantee that the net force is zero.

Conclusion
The correct answer is option 'A' because only when two forces act in opposite directions with equal strength can they result in a net force of zero. In all other scenarios, the forces will either add up or not completely cancel out, leading to a non-zero net force. Understanding these principles is crucial in physics, especially when analyzing motion and equilibrium.

Leaves or fruits fall on the ground due to gravitational force. Gravitational force is the force of attraction between two objects with mass. It is what keeps all of the planets in orbit around the sun and what causes objects to fall towards the ground when dropped. The other forces listed, such as magnetic force, electrostatic force, and muscular force, are not responsible for causing leaves or fruits to fall on the ground.