Force and Pressure NCERT Science Class 8 Summary Note

Force 
The push or pull of an object, is called force. 

Forces are due to interaction between objects. 

Force applied on an object in the same direction add to each other. 

Force applied on an object in opposite directions substract each other. 

The strength of force is measured by its magnitude. 

A force can change the state of motion of an object. 
Change in state of motion jeans
Rest to motion
Motion to rest 
Increase in speed 
Decrease in speed

Force on an object may change its shape. 

Types of forces 
Contact force 
The force that can be applied only by touching object,is called contact force. 

Non-Contact force 
The force that can be applied without touching object,is called contact force. 

Muscular force 
The force resulting due to action of muscles is called muscular force. 

Friction
The force that oppose motion of an object. 

Magnetic force
The force exerted by a magnetic material is called magnetic force. 
Like pole repel each other. 
Unlike pole attract each other. 

Electrostatic force
The force exerted by a charged body , is called electrostatic force. 
Like charge repel each other. 
Unlike charge attract each other. 

Gravitational force 
The force of attraction between two objects, is called gravitational force. 

Gravity 
Force of attraction between any object and earth is called gravity. 

Pressure
The force acting on a unit area , is called pressure. 
Pressure= Force /Area 


Both gas and liquid exert pressure on wall of container. 

Atmosphere
The blanket of air around us is called atmosphere. 

Atmospheric pressure
The pressure exerted by air, is called atmospheric pressure. 




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