Chapter 11 Force and Pressure Class 8 Notes | EduRev

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Class 8 : Chapter 11 Force and Pressure Class 8 Notes | EduRev

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Chapter – 11 Force and Pressure 
Force 
Force – A pull or a push is called force. The unit of force is Newton (N) 
1. Forces applied in same direction add apply greater force on an object. 
2. Forces applied in opposite directions subtracts to reduce the total applied force on an object. 
The amount of force applied on an objects is called its magnitude. For e.g. John applies 5N force towards left on 
an object. 5N is the magnitude of the force and towards the left is the direction of the force. 
 
State of motion – It is the state of an object determined by its speed and direction of motion. 
Effects of force on state of motion: 
1. Force can move a stationary object.  
2. Force can change the direction of a moving object. 
3. Force can increase the speed of a moving object. 
4. It can reduce the speed of a moving object. 
5. It can change the shape of an object. 
6. Force can stop a moving object if applied in opposite direction of motion. 
 
Types of Forces –  
1. Contact Forces – Force that can only be applied by touching the object. 
 
a. Muscular Force – The force produced by pulling or pushing through our muscles. E.g. 
pulling a rope, or pushing a car. 
 
b. Frictional force – Force acting between two surfaces that slows down or stops a moving 
object. For e.g. a moving ball stops at some distance due to friction between the ball and the 
ground or floor. 
 
2. Non-Contact Forces – Force that can be applied without directly touching the object. 
 
a. Magnetic Force – Two magnets pull of push each other without even getting in touch with 
each other. Magnets have two poles north pole and south pole. Same poles repel each other 
and opposite poles attract each other. 
 
b. Gravitational Force – The attractive force between two objects due to their mass. E.g. A 
pen thrown upward falling towards the Earth. All the objects attract each other by 
gravitational force but their mass is very small so the force among various objects is 
negligible. 
 
 
c. Electrostatic force – A force between one charged and another charged or uncharged object 
is called electrostatic force. For e.g. when we rub a comb with our hair, it get charged and it 
Page 2


Chapter – 11 Force and Pressure 
Force 
Force – A pull or a push is called force. The unit of force is Newton (N) 
1. Forces applied in same direction add apply greater force on an object. 
2. Forces applied in opposite directions subtracts to reduce the total applied force on an object. 
The amount of force applied on an objects is called its magnitude. For e.g. John applies 5N force towards left on 
an object. 5N is the magnitude of the force and towards the left is the direction of the force. 
 
State of motion – It is the state of an object determined by its speed and direction of motion. 
Effects of force on state of motion: 
1. Force can move a stationary object.  
2. Force can change the direction of a moving object. 
3. Force can increase the speed of a moving object. 
4. It can reduce the speed of a moving object. 
5. It can change the shape of an object. 
6. Force can stop a moving object if applied in opposite direction of motion. 
 
Types of Forces –  
1. Contact Forces – Force that can only be applied by touching the object. 
 
a. Muscular Force – The force produced by pulling or pushing through our muscles. E.g. 
pulling a rope, or pushing a car. 
 
b. Frictional force – Force acting between two surfaces that slows down or stops a moving 
object. For e.g. a moving ball stops at some distance due to friction between the ball and the 
ground or floor. 
 
2. Non-Contact Forces – Force that can be applied without directly touching the object. 
 
a. Magnetic Force – Two magnets pull of push each other without even getting in touch with 
each other. Magnets have two poles north pole and south pole. Same poles repel each other 
and opposite poles attract each other. 
 
b. Gravitational Force – The attractive force between two objects due to their mass. E.g. A 
pen thrown upward falling towards the Earth. All the objects attract each other by 
gravitational force but their mass is very small so the force among various objects is 
negligible. 
 
 
c. Electrostatic force – A force between one charged and another charged or uncharged object 
is called electrostatic force. For e.g. when we rub a comb with our hair, it get charged and it 
can attract pieces of paper without actually touching them. The force that pulls the pieces of 
paper is electrostatic force. 
 
Pressure 
Pressure – force applied per unit area is called pressure. 
    Pressure = Force/Area        (Area of the object on which the force is applied) 
 Units of pressure = N/m
2
   
 
The pressure increases as the force is increased as the numerator will increase. 
The pressure decreases as the area is increased as the denominator will increase. 
 
It is advised to wear shoes with large surface area on sand and snow to increase the surface area so that less 
pressure is applied on the surface. Heels have low surface area and apply large pressure on sand and snow, so 
are easily stuck inside. 
 
Liquids and gases exerts pressure on the walls of the containers.  
 
 
 
Another example of suction through the straw. I we such water from a bottle through a straw, quickly close the 
mouth of the straw with our finger, and take the straw out of the bottle. The water will on fall from the other end 
because  of the pressure applied by the water on the walls and the finger.       
 
Atmosphere – The air around us is called atmosphere.  
Atmospheric pressure – The pressure exerted by this envelope of air is called atmospheric pressure.        
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