## Introduction of Newton's Laws.

- Today in this article I will discuss on Newton's famous laws which will be beneficial for school going students of Class 9 and Class 10.

## .-

# Newton's laws of motion:-

- 1st law of motion:-

- If no external force is exerted on a body which is in uniform motion will remain in motion and a body which is at rest remains at rest. This is called Newton's 1st law of motion.

- From Newton's 1st law of motion we can know two principles of matter:-

- 1. Principle of inertia of a body

- 2. Defination of force.

- Inertia at rest:- It is a property of all regid bodies by virtue of which a body which is at rest remains at rest unless no external force is applied on them.

- Force :- Force is an external agency which is when applied on a body changes the state of motion or state of rest of a body or tries to change the state of a body. It is denoted by 'F' ; It is a vector quantity and its S.I unit is Newton.

- 2nd law of motion:-

- Rate of change of momentum of a moving body is directly proportional to its applied force.i.e;

- F∞ (mv - mu)/t

- => F= k.m(v-u)/t [ where 'k' is proportionality constant]

- 3rd law of motion :-

- Every action there is an equal and opposite reaction, action and reaction both takes place simultaneously together at same time.

## Newton's law of Gravitation:-

- In this universe, every object attracts another object with respect to earth,the force of attraction between two objects is directly proportional to the product of their masses and inversely proportional to the square of their distance.

## Illustration :-

- The mass of 1st object =M
- The mass of 2nd object = m
- distance between them = r
- and force of attraction = F Now,
- According to the law of gravitation,
- F∞ M.m…..(1)
- and F∞ 1/r²…..(2)
- Now from (1) and (2) we get,
- F∞Mm/r²
- => F= GMm/r²,[ Where 'G is a variation constant ,called gravitational constant], This law is also known as Newton's Universal law of gravitation.

## Using Newton's 2nd law of motion ,Prove that F=ma

## Using Newton's 2nd law of motion ,Prove that F=ma

### Answer:-

- In the picture, At position A,
- A body has a mass =m
- It has initial velocity = u
- In this case,
- its momentum = mu
- After applying a force F in a duration of 't' sec the body moves from A to position B
- Now the final velocity of the body is = v
- So, in this case,its momentum is = mv
- ∴ Change in momentum = mv - mu
- So, rate of change of momentum of the body = (mv-mu)/t
- Now,
- according to Newton's 2nd law of motion,
- F∞ (mv-mu)/t
- => F= Km(v-u)/t
- =>F =Kma [∵ (v-u)/t =a, where a is accleration of the moving body]...(1)
- Now, if F= 1 Newton
- m= 1 kg
- and a = 1 m/ s²
- then, from (1) we get,
- 1=K .1.1
- =>K =1
- Again from (1)
- F = 1.ma [ Putting K=1]
- => F = ma Proved.

## Formulae which are used to solve uniform motions problems are :-

- 1. S = Vt , where S is the distance travelled by the moving body, V is the velocity of the body and t being the time.

- 2. v = u + at , [ In case of acceleration]

- where, u is Initial velocity of the moving body, a is acceleration of the moving body and t is the time taken by the body to travel.

- 3. v = u - at [ In case of retardation.]

- 4. S = ut + ½ at² [ In case of acceleration]

- 5. S = ut - ½ at² [ In case of retardation]

- 6. V² = u² + 2aS [ In case of acceleration]

- 7. V² = u² - 2aS [ In case of retardation]

## Formulae for falling body under earth gravity in uniform motion:-

#### 1.v = u+ gt [ falling towards the direction of earth centre],Where,g = acceleration due to gravity of earth

2.v = u- gt [ opposite of earth gravity]

3.v² = u² + 2gS

4.v² = u² - 2gS

5.S = ut + ½ gt²

6.S = ut - ½ gt²

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## FREQUENTLY ASKED QUESTIONS:-
##
How many motion's law Newton have?

Answer :- There are three types of Newton's law of motion and they are:-
(i) 1st law of motion or law of inertia.
(ii) 2nd law of motion
(iii) 3rd law od motion.

## Newton's which law is also known as law of inertia?

Answer:- Newton's 1st law is also known as law of inertia.

## Newton's which law gives us the defination of force?

Answer:- Newton's 2nd law gives us the defination of force.

## what are the differences between 'g' and 'G' ?

Answer :- Answer: The differences between 'g' and 'G' are :-(i) g is called acceleration due to earth gravity where as G is known as gravitational constant of earth. (ii) The value of g is variable depending upon place to place but G is always constant in the universe.

##
Newton's which law is called law of action and reaction?

Answer:- Newton's 3rd law of motion.

##
What is Gravitational law ?

.
Answer :- In this universe every body attracts another body with respect to earth, this force of attraction is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
Mathematically Gravitational law can be illustrated as:-
The mass of 1st object =M
The mass of 2nd object = m
distance between them = r
and force of attraction = F Now,
According to the law of gravitation,
F∞ M.m…..(1)
and F∞ 1/r²…..(2)
Now from (1) and (2) we get,
F∞Mm/r²
=> F= GMm/r²,[ Where 'G is a variation constant ,called gravitational constant], This law is also known as Newton's Universal law of gravitation.

##
Examples of scaler and vector quantities?

Answer:- Scaler quantities :- Distance,time,length, speed……
vector quantities :- Displacement,Velocity,acceleration,force….

## How many motion's law Newton have?

Answer :- There are three types of Newton's law of motion and they are:- (i) 1st law of motion or law of inertia. (ii) 2nd law of motion (iii) 3rd law od motion.

## Newton's which law is also known as law of inertia?

Answer:- Newton's 1st law is also known as law of inertia.

## Newton's which law gives us the defination of force?

Answer:- Newton's 2nd law gives us the defination of force.

## what are the differences between 'g' and 'G' ?

Answer :- Answer: The differences between 'g' and 'G' are :-(i) g is called acceleration due to earth gravity where as G is known as gravitational constant of earth. (ii) The value of g is variable depending upon place to place but G is always constant in the universe.

## Newton's which law is called law of action and reaction?

Answer:- Newton's 3rd law of motion.

## What is Gravitational law ?

. Answer :- In this universe every body attracts another body with respect to earth, this force of attraction is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. Mathematically Gravitational law can be illustrated as:- The mass of 1st object =M The mass of 2nd object = m distance between them = r and force of attraction = F Now, According to the law of gravitation, F∞ M.m…..(1) and F∞ 1/r²…..(2) Now from (1) and (2) we get, F∞Mm/r² => F= GMm/r²,[ Where 'G is a variation constant ,called gravitational constant], This law is also known as Newton's Universal law of gravitation.

## Examples of scaler and vector quantities?

Answer:- Scaler quantities :- Distance,time,length, speed…… vector quantities :- Displacement,Velocity,acceleration,force….

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