## Class 8 Science Chapter 11 Notes Force And Pressure Notes

In this post, we will discuss Class 8 Science Chapter 11 Notes Force And Pressure Notes. Class 8th science ch 11 notes help students in revision. Force And Pressure notes class 8, we will learn about Force, Type of Force and pressure. You can also download the Force And Pressure notes class 8 pdf for further study. NCERT notes for the Class 8 Science Chapter 11 are designed by our subject expert team.

In this Class 8th Science Ch 11 Notes pdf, we will learn about Force And Pressure.

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## Class 8 Science Chapter 11 notes Overview

In class 7 you have learnt how objects move. You also know that a moving object like a ball rolling on the ground Slow Down after some time. it may go faster or change the direction of motion. Have you ever noticed why all these tasks are done? This is because of force.

Here we study Force and Pressure.

## Force

A push or pull on an object is called force. Or force is any action that has the tendency or tries to change the position shape or size of the object.

If two forces are applied in the opposite direction the net force is given by the difference between the two forces.

If two forces are applied to an object in the same direction then the resultant force adds to one another.

### Due to force following action can be done

• Force can move a body which is initially at rest.
• Force can stop the moving object.
• Force can change the direction of moving objects.
• force can change the direction of the moving body.
• force can change the shape of the body.
• force can change the size of the body.
• Force means the interaction of one object with another object.

## Type of Force

1. Contact force
2. Non- Contact force

### Contact force

Contact forces:- Force which required touch or contact is called contact force. our everyday activities like pulling, and pushing include contact force.

Some contact forces are as follows

#### Muscular Force

Muscular force involves the action of muscles for example animals make use of muscles for doing many physical activities.

#### Friction Force

• Recall some experience.
1. A ball rolling on the ground gradually slow down and finally come to rest.
2. When we stop paddling a bicycle it gradually slows down and finally comes to rest.
• In all situations, you know why all these things slow down and finally come to rest is because of frictional force.

Now, what do you mean by frictional force?

The force that required the relative motion between the two surfaces is called frictional force.

• The direction of the frictional force is always opposite to the direction of motion.
• Frictional force always acts between two moving objects that are required contact.
• The frictional force is a type of contact force.
• The frictional force depends on the nature of the surface in contact.
• A smooth surface has less frictional force whereas a rough surface has more frictional force.

### Non-Contact force

Non-contact force:- The force which has its influence without touch or force that does not require contact.

Some Non-Contact forces are as follows

#### Magnetic force

• Force acting between the two magnets or a magnet and a magnetic material like iron steel etc.
• It can be an attractive or repulsive force.
• A magnet has two poles South Pole and the north pole.
• The same pole attracts i.e north-North and South-South Poles attract.
• Different pole repels i.e north-south and south-north pole Repulse.

#### Electrostatic Force

Force due to electric charge is called electrostatic force it can be attractive and repulsive. The force exerted by a charged body on another charge or uncharge body is known as electrostatic force full stop this Force comes into play when the bodies are not in contact. The electrostatic force is a non-contact force.

#### Gravitational Force

Recall Some experience

• A coin or a pen falls to the ground when it slips off your hand.
• Leaves and fruits also fall to the ground when they get detached from the plant. Have you ever wondered why it is so?

Objects or things fall towards the earth because it pulls them. This force is called the force of gravity, or just gravity. This is an attractive force. The force of gravity acts on all objects.

Gravity is not a property of the earth alone. In fact, every object in the universe, whether small or large, exerts a force on every other object. This force is known as the gravitational force.

## Pressure

The force acting on a unit area of a surface is called pressure. Or pressure is force per unit area.

pressure = force / area on which it acts

• The smaller the area, the larger the pressure on a surface for the same force that’s why porters place a round piece of cloth on their heads, when they have to carry heavy loads. By doing this they increase the area of contact of the load with their head. So, the pressure on their head is reduced.
• Liquids and gases also exert pressure.
• Liquids and gases exert pressure on the walls of the container

### Atmospheric Pressure

Air is all around us and this envelope of air is known as the atmosphere. The atmospheric air extends up to many kilometres above the surface of the earth. The pressure exerted by this air is known as atmospheric pressure.

## What we learn in Class 8 Science Chapter 11 Notes Force And Pressure

In Class 8th Science Ch 11 Notes pdf / Force And Pressure notes

• Force could be a push or a pull.
• A force arises due to the interaction between two objects.
• Force has magnitude as well as direction.
• A change in the speed of an object or the direction of its motion or both implies a change in its state of motion.
• Force acting on an object may cause a change in its state of motion or a change in its shape.
• A force can act on an object with or without being in contact with it.
• Force per unit area is called pressure.
• Liquids and gases exert pressure on the walls of their containers.
• The pressure exerted by the air around us is known as atmospheric pressure.

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