# NCERT Class 8th Chapter -11: Force and pressure

Updated Thu, 02 Jun 2022 12:58 AM IST

## Highlights

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When an object is pushed or pulled, it is called a force. The motion produced in an object is due to the action of force.

 What is force Law of force Types of force Contact force Muscular force Frictional force What is pressure?

For example- A force exerted on an object causes the table to move in a certain direction. The strength of a force is usually expressed in terms of magnitude. Power also has a direction. Likewise, if there is a change in size or direction, it directly affects the force.

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Source: Amar ujala

If the force is exerted in the opposite direction to the direction of motion, it causes a decrease in the speed of the object. If an object is in motion, an external force can change the position or direction of motion of that object. The state of motion of an object can be expressed by the speed and direction of its motion. The “at rest” state of an object is considered zero speed because no object can change its speed on its own. No object can change direction on its own. A force can move an object from rest. A force can change the speed of a moving object. A force can change the direction of a moving object. A force can try to change the shape of an object.

The force caused by muscle action is known as muscle strength. Any force that slows the speed of a moving object is called “friction”. Road wheel; As soon as the power source stops working, the frictional force stops this wheel.

### Laws of force-

• All forces acting on an object in the same direction. Together they form a mighty force.
• A force applied in the opposite direction reduces the force acting on that object. The total force in this will be equal to the difference between the two forces.
• Rather, strength is measured by its outcome.
• The shape of any object changes when a force is applied.
• There is a change in the speed of any object when a force is applied.

### Types of Force

There are mainly two types of force…..

1. Contact force
2. Non-contact force

### Contact force -

Contact force is exerted by the interaction of two objects with each other. We can divide this force mainly in two ways.

### Muscular force -

The force exerted by an animal is called muscular force. Muscles are needed to exert this force. For example, the bull is pulling a cart.

### Frictional force -

This force is exerted by the movement of two objects with each other. This force is acting on every object. This force acts in the opposite direction of motion.

## What is pressure?

• The force acting on a unit area of a surface is called pressure (pressure = force/area it acts on).The envelope of air that extends several kilometers above the earth’s surface is called the atmosphere.

The pressure affected by air is called atmospheric pressure.The pressure inside our body is exactly equal to the atmospheric pressure and eliminates the pressure coming from outside.

## Q1-What is the force in short?

Answer -force is a push or pull upon an object resulting from the object's interaction with another object. Whenever there is an interaction between two objects, there is a force upon each of the objects.

## Q2-What is the importance of force?

Answer- Forces are important because, as we learned in another lesson, they are responsible for changes in motion. In fact, Isaac Newton describes this in his first law. This law of inertia states that an object continues in its state of rest or motion unless acted on by an outside unbalanced force.

## Q3-What is the effect of force?

Answer -Force can. Move stationary object. Stop moving object. Change speed of the object. Change direction of a moving body

## Q4-What is the unit of force and pressure?

Answer -The unit of force is Newton and the unit of pressure is Pascal

## Q5-What is the characteristic of force?

Answer -Characteristics of Force:
Forces are due to an interaction of at least two objects.
It may change the state of motion of an object.
It may change the shape of an object.
Forces applied on an object in the same direction add to one another and the resultant is in the same direction.

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