8th Force and Pressure

  class 8th science

ICSE/ CBSE Notes-

For more Notes click this link https://cbsenotesallsub.blogspot.com/

Force

Force

• The push or pull on a body is known as force 
•  The direction in which the body push or pull is called direction of force
• It  enables us to do any  work 
• Unit of force is Newton
• Force = mass  x acceleration  (F = ma)

Eg- Stretching a rubber band

       A football player kicking the ball

       A boy lifting the bucket 

      Open or close the door   etc

For more Notes click this link https://cbsenotesallsub.blogspot.com/

Effect of  Force

• Force can Move a stationary body and  stop the moving body

• Force can change the speed and direction of the body

For more Notes click this link https://cbsenotesallsub.blogspot.com/

• Force can change the shape and size of the body
• Force increases the speed of the moving body.

• Force stop or reduces the speed of a moving object
  
  
  
  
  
  
  
  
  .

For more Notes click this link https://cbsenotesallsub.blogspot.com/

Types of Forces

There are two types of forces which are given below.

1. Contact force
2. Non contact force

1- Contact force

It is the force that is exerted by one object to another object when they are contact to each other is called contact force.

Eg- Frictional force between road and  vehicle 

Friction The friction force is the force exerted by a surface as an object moves across it or makes an effort to move across it.

• Frictional force refers to the force generated by two surfaces that contacts and slide against each other.
• Friction force occur between two surfaces.
• Direction of friction force is in opposite of applied force.
• Force exerting by machine is called mechanical force.

Friction between both surfaces

For more Notes click this link https://cbsenotesallsub.blogspot.com/

2- Non contact force

It  is the force exerted by one object over the another when both two objects are not physically in contact are called non contact force

  

Eg- Gravitational force ,magnetic force etc

• Falling of  apple  due to gravitational force.

• Gravitational force

• Movement of planet around the sun due to gravity between them.

• Planet moves due to gravitational force

For more Notes click this link https://cbsenotesallsub.blogspot.com/

• Attraction  and  Repulsion force are occur between to charge 
• Same charge repel to each other , different charge attract to each other.

• Magnetic force of attraction take place when any iron pin placed near it

For more Notes click this link https://cbsenotesallsub.blogspot.com/

• Opposite poles are attract to each other.
• Same poles are repel to each other.

For more Notes click this link https://cbsenotesallsub.blogspot.com/

Pressure

• Force acting per unit area is called pressure.
• Pressure = Force / Area

• The SI Unit of  Pressure is N/m2  or Pascal 
• If applied force is  maximum then Maximum Pressure exerted.
• To increase the pressure applied to any object increases the amount of force applied.So, greater the force greater would be the pressure applied. 
• If contact area is maximum then minimum pressure exerted.
• You can increase pressure due to the same force by reducing the amount of area over which the force is acting.
• 

eg  

• Pushing of  sharp knife for cutting the vegetables.

For more Notes click this link https://cbsenotesallsub.blogspot.com/

Distribution of pressure

• Force acting on a smaller area applies more pressure than the same force acting on a larger area.
• Examples: Porters place a round cloth on their heads to increase surface area and reduce pressure.
• A sharp knife cuts better as more pressure is exerted over a smaller area.

Pressure in fluids

• The pressure exerted by a fluid(gases or liquids) in a container is transmitted undiminished in all direction on the walls of the container.

Upthrust

• The upward force exerted by a fluid on an object is known as upthrust or buoyant force.
• Pressure exerted by water  according to newtons third law (every action have equal and opposite reaction)

Atmospheric Pressure

Gaseous pressure

• Gases exert the same pressure on the walls of the container in all directions.

Atmospheric pressure

• Our atmosphere extends to several kilometres above sea level. The weight of the air acts as pressure known as atmospheric pressure.
• The pressure in our body balances the atmospheric pressure and that is why we do not feel it..

For more Notes click this link https://cbsenotesallsub.blogspot.com/

            

***********************