Test: Force And Pressure - 4 - Class 8 MCQ

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

The strength of a force is expressed by its magnitude. The magnitude of a force is expressed in the SI unit of force called Newton. 1 Newton is the force which can make an object of 1 kilogram mass to move at a speed of 1 meter per second. The direction in which a force acts is also to be specified.

The force between two charged bodies is called:

- Electrostatic force.

Solution:
- The electric force between two charged bodies at rest is known as electrostatic force or Coulomb force.
- This force is described by Coulomb's law, which states that the magnitude of the electrostatic force between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.
- Electrostatic forces can be either attractive or repulsive depending on the nature of the charges involved.The electric force between two charged bodies at rest is conventionally  called electrostatic force or Coulomb force.

The state of rest or motion of an object is defined using a reference point. The reference point is a point used to describe the location of something. An object is said to be in motion, if it changes its position relative to the reference point. The mass, volume and size of the object are not necessary to describe whether the object is at rest or in motion.

Magnetic forces are non - contact forces;  they pull or push on objects without touching them. Magnets are only attracted to a few 'magnetic'  metals and not all matter.

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:
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 the force that pulls objects towards the center of the Earth.
- When leaves or fruits are detached from the tree or plant, the only force acting on them is gravity.
- Gravity pulls the leaves or fruits downwards towards the ground, causing them to fall.
- This is because all objects with mass are subject to the gravitational force, and the force is directly proportional to the mass of the object. Therefore, larger and heavier leaves or fruits are pulled down more strongly by gravity.
- The gravitational force also depends on the distance between the object and the center of the Earth. The closer an object is to the Earth's surface, the stronger the gravitational force.
- As a result, when leaves or fruits fall from the tree, they accelerate towards the ground under the influence of gravity until they reach the surface.
In summary, leaves or fruits fall on the ground due to the gravitational force, which is the force of attraction between objects with mass.

Otto von Guericke was a German scientist, inventor, and politician. His major scientific achievements were the establishment of the physics of vacuums, the discovery of an experimental method for clearly demonstrating electrostatic repulsion, and his advocacy of the reality of "action at a distance" and of "absolute space".

Explanation:

The force of friction is actually an example of a contact force, not a non-contact force. Friction occurs when two surfaces come into contact with each other and resist the relative motion between them. It is caused by the microscopic irregularities on the surfaces that interlock and create resistance to motion. Here's why the force of friction is a contact force:

- Contact force: A contact force is a force that acts between objects that are physically touching each other. The force of friction is a contact force because it only occurs when two surfaces are in direct contact with each other.
- Nature of friction: Friction is a force that opposes the motion of an object. When two surfaces are in contact, they experience a force of friction that resists their relative motion. This force can be either static friction (when the surfaces are not moving with respect to each other) or kinetic friction (when the surfaces are sliding past each other).
- Causes of friction: Friction is caused by the interlocking of microscopic irregularities on the surfaces. These irregularities create resistance to motion, resulting in the force of friction.
- Examples of contact forces: Some examples of contact forces include the force of gravity, normal force, tension force, applied force, and friction. All of these forces require physical contact between objects to occur.
In conclusion, the force of friction is an example of a contact force, not a non-contact force. It occurs when two surfaces are in direct contact and resists their relative motion.

Explanation:

When two forces act on an object in opposite directions, the net force on the object is indeed the difference between the magnitudes of the two forces. The direction of the net force will be in the direction of the larger force.

For example, if a force of 10 N acts to the right and a force of 4 N acts to the left on the same object, the net force will be:

The net force is 6 N to the right. Thus, the statement is true.

A lubricant is a substance, usually organic, introduced to reduce friction between surfaces in mutual contact, which ultimately reduces the heat generated when the surfaces move. It may also have the function of transmitting forces, transporting foreign particles, or heating or cooling the surfaces.

The correct answer is B as force exerted per unit area is called pressure.

If the force applied on the object is in the direction of its motion, the speed of the object increases. If the force is applied in the direction opposite to the direction of motion, then it results in a decrease in the speed of the object. Thus, a force may bring a change in the state of motion of an object. 

Muscular force is a type of contact force that occurs when muscles contract and exert a force on an object. Here is a detailed explanation of why muscular force is a kind of contact force:
Definition of contact force:
- Contact force is a force that occurs when two objects are in direct contact with each other. It is a force that is transmitted through physical contact between objects.
Muscular force as a contact force:
- Muscular force is generated within the muscles of living organisms, such as humans and animals.
- When a muscle contracts, it exerts a force on the object it is in contact with, causing a physical interaction.
- The force generated by the muscle is transmitted through the points of contact between the muscle and the object.
- This force can be used to move or exert pressure on the object, leading to various actions and movements.
Examples of muscular force as a contact force:
- When a person lifts a heavy object, the muscles in their arms contract, exerting a force on the object through direct contact.
- During sports activities, muscles generate force to kick a ball, throw a javelin, or swim through the water.
- Animals use muscular force to walk, run, jump, or fly by exerting force on the ground or air through direct contact.
Key points:
- Muscular force is a type of contact force because it requires direct physical contact between the muscle and the object.
- This force is produced by the contraction of muscles and is transmitted through points of contact.
- Muscular force allows living organisms to interact with their environment and perform various actions and movements.
In conclusion, muscular force is indeed a kind of contact force as it involves direct physical contact between the muscles and the object, and the force is transmitted through this contact.

Explanation:
Gravity is a force that attracts objects towards each other. It is a non-contact force, meaning it does not require physical contact between objects for it to act. Instead, it acts over a distance.
Here is a detailed explanation of why the statement "Force of gravity is a contact force" is false:
Definitions:
- Contact force: A contact force is a force that acts when two objects are in physical contact with each other.
- Non-contact force: A non-contact force is a force that acts even when two objects are not in physical contact with each other.
Force of gravity:
- The force of gravity is an example of a non-contact force.
- It is the force that attracts objects with mass towards each other.
- It is responsible for keeping planets in orbit around the sun, holding objects on the surface of the Earth, and many other phenomena.
Characteristics of the force of gravity:
- Acts over a distance: The force of gravity acts between objects regardless of whether they are in physical contact or not.
- No direct physical contact: Objects do not need to be in physical contact for the force of gravity to act between them.
- Dependent on mass: The force of gravity depends on the mass of the objects involved. The greater the mass, the stronger the force of gravity.
Examples:
- Planetary motion: The force of gravity keeps planets in orbit around the sun. The planets are not in physical contact with the sun but are still under its gravitational influence.
- Falling objects: When an object falls towards the Earth, it is being influenced by the force of gravity. There is no physical contact between the object and the Earth until they come into contact with each other.
Therefore, the statement "Force of gravity is a contact force" is false. Gravity is a non-contact force that acts over a distance.

 

Yes, at least two objects must interact for a force to come into play. Force is a push or pull between two objects, and it can happen through contact or without contact. 

The Pascal is the Si unit of Pressure. Whereas the Si unit of force is  Newton. 
So, the given statement is false.

To move an object faster it has to be pushed or pulled repeatedly. 

Pull:-  Applying force in a direction towards us is known as pull. 

Push:- Applying force in a direction away from us is known as push.