* Newton’s First Law Of Motion:-* When an object changes its location relative to time relative to other objects, then this state of the object is called motion. If there is no change in the position of the object with respect to time, then the object is at rest and if the position of the object changes with time, then the object is in the state of motion.

**Equation of the first law of motion**

v = u + at

Where

v = velocity

u = initial velocity

a = acceleration

t = time

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## Newton’s First Law of Motion

Newton’s first law of motion is also called Galileo or the law of inertia. According to this law, if an object is at rest, it will remain at rest and if it is moving in a straight line with uniform velocity (zero acceleration) then it will remain in motion as long as its current No external force should be applie to change the state.

The motion of an object at constant or with the same velocity, both are states of zero acceleration, for change in these states, external force is necessary.

## Example of Newton’s first law of motion

Newton’s first law defines inertia, there are three types of inertia

1. Static Inertia

2. Dynamic Inertia in Dynamic State

3. Inertia of Direction

**(1) Static Inertia in a steady state**

According to this law, if an object is stationary in the absence of an external force, it will remain in a stationary state. This is called the law of inertia in the steady state.

**Examples of inertia in steady state**

(i) If a stationary bus is suddenly accelerate, then the lower part of the passenger sitting in the bus will start moving with the bus, while the upper part will try to remain stationary due to inertia. Due to this, the passenger of the bus will get pushed backwards.

(ii) When a shot of a gun is fired at a glass window, other than the point of impact of the bullet, due to inertia, the other part of the glass remains in a fix state and does not crack. Because of this, there is only a bullet-shaped hole in the glass.

(iii) By placing a cardsheet over a glass, put a coin in a stationary state and remove the card sheet by hitting it sharply with a finger, then the card sheet will move away and the coin will fall into the glass by remaining on the glass due to inertia in the stationary state. .

(iv) When the blanket is shaken, the soil particles are separated from it. When the blanket is shaken, the blanket becomes dynamic, while the soil particles located in it try to remain stationary. So they separate from him.

(v) If the bus is moving slowly, then the inertia of the motion is transmitted uniformly in the body of the person, so that the whole body of the person moves with the bus and the person does not get any shock.

### **( 2 ) Inertia in the moving state ( Dynamic Inertia )**

According to this law, an object moving with the same velocity cannot accelerate or slow down by itself (without applying force), that is, a moving object tries to remain in motion continuously.

**Examples of inertia in motion**

(i) When a passenger in a train moving with a constant velocity tosses the ball upwards, it again falls into the passenger’s hand because due to the inertia of motion, the ball remains in motion in the direction of motion of the train even though it is in the air.

(ii) When a passenger disembarks from a moving bus, his feet stop on contact with the road, but the upper part of the body moves forward due to the inertia of the moving state and the passenger falls in the direction of motion of the bus.

(iii) The fast bowler of cricket runs fast on the long run-up before throwing the ball so that the extra velocity gained by his running may increase the effective velocity of the ball thrown by him.

(iv) When a moving bus applies the brakes suddenly, the upper part of the body of the passenger sitting in the bus keeps the motion forward due to mobility and the passenger gets a jolt forward.

** ( 3 ) Inertia of Direction**

According to this law, a moving object cannot automatically change the direction of its motion. That is, in the absence of external forces, the object will continue to move along a straight line.

**Examples of inertia of direction**

(i) If a stone is tied to a thin string and rotated in a circular path in the horizontal plane, and if the string is suddenly broken in the event of motion, then the stone tied to the string can no longer move in the circular path, but in the tangential direction along the circumference of the circle. Moving away, he moves away.

(ii) A rotating wheel of a vehicle throws mud outwards along the tangent to the wheel, due to the inertia of this direction.

## Important facts about inertia

1. Inertia has no unit or dimension.

2. Inertia is not a physical quantity, it is only an inherent property of the object which depends on the mass of the object.

3. There are two objects of equal mass, one of which is moving and the other is stationary. Both have the same value of inertia because inertia depends only on mass. It does not depend on the velocity and size of the object.

4. Inertia means resistance to change.