Force class 8to9 full detailed notes 2023

                  FORCE 《CLASS -- 9TH》

● Push and pull on an object is called Force.

■ EFFECT OF FORCE:

FORCE CAN_

• Move a stationary object.

• Stop a moving object.

• Change the speed of a body.

• Change the direction of a body

• Change the shape and size of the body.

A force can act on an object by: _

1. Pushing

2. Pulling                                    

3. Lifting

4. Stretching 

5. Compressing or

6. Twisting 

● Types of force :_

BALANCED FORCE

The net resultant force acting on an object is zero then the force is called balanced force.

~ A balanced force can change the shape and size of the body.

~ A balanced force can't produce motion in the body.

EXAMPLE. 

Squeezing of toothpaste etc.

UNBALANCED FORCE

If the net resultant force acting on a body is not zero then the type of force is called unbalanced force.

~A unbalanced force can't change the shape and size of the body.

~A unbalanced force can produce motion in a body.

EXAMPLE. 

Falling of object from some height and some distance etc.

          NEWTON'S LAWS OF MOTION 

                   

                    FIRST LOW

According to NEWTON'S 1st law of motion, a body in rest will remain be in rest or a body in motion will remain be in uniform motion in a straight line unless it is compelled by some external force to change its state of rest or uniform motion.

** NEWTON'S 1st LAW OF MOTION IS ALSO KNOWN AS GALILEOS LAW OF INERTIOA.

● INERTIA :

Inertia is the property of matter due to which it resist any changes in its position of rest or uniform motion.

# Mass is the measure of inertia.

                             2ND LAW 

                   

According to NEWTON'S 2nd law of motion the rate of change in momentum is directly proportional to applied force and take place in the direction of force.

So, According to Newtons 2nd law of motion 

 

        { F ∝ rate of change in momentum }

> F ∝ change in momentum ÷ time

> F ∝ (final momentum - initial momentum)÷ time    

> F ∝ (mv - mu)÷time

> F ∝ m(v-u)÷t

> F ∝ ma [ (v-u)÷t = a ]

> F = kma [ where k is constant of proportionality ].

   

 ● F= ma

• The SI unit of force kgm/s² or Newton or N.

We know _

                F = ma

1N = 1kg × 1 m/s²

• 1 newton is the force which when acts on a body of mass 1kg produces an acceleration of 1m/s².

                    3rd law of Motion

To every action there is equal and opposite reaction.

> • The action and reaction do not take place in the same body.

☆☆ Mathematically, Newtons third law is 

        give by __

                       F1 = F2

> Forces always exist in pairs .

   LAW OF CONSERVATION OF MOMENTUM 

According to law of conservation of momentum " whenever two or more bodies acts upon one another their total momentum remain constant. 

In other words, 

         Momentum can neither be created nor be destroyed. 

Therefore, 

Total initial momentum = total final momentum                                                              

                    ☆ TIM = TFM.

 

          📖 😊 THANKS FOR READING 📚 😀