INERTIA:

 

Newton’s first law gives the definition of inertia , according to which an object cannot change its state by itself. If the object is in the state of rest , it will remain in the state of rest and if it is moving in some direction, it will continue to move with the same speed in the same direction unless an external force is applied on it.

Example-A book lying on a table to will remain placed unless it is displaced. Similarly, a ball rolling on a horizontal plane keeps on rolling unless the force of friction between the ball and the plane stops it.

                “The property of an object by virtue of which it tends to retain its state of rest or of motion, is called inertia. It is the inherent property of each object.”

 

INERTIA IS OF THE FOLLOWING TWO KINDS:

1-      INERTIA OF REST
2-      INERTIA OF MOTION

 

INERTIA OF REST:

                If a body is at rest, it will remain at rest unless an external force is applied to change its state of rest. This property of body is called the inertia of rest.


EXPLAIN THE FOLLOWING:


1-When a train suddenly starts moving forward, the passenger standing in the compartment tends to fall backwards, why?


Ans-The reason is that the lower passenger’s body is in close contact with the train, starts moving , his lower part shares the motion at once, but the upper part due to inertia of rest cannot share the motion simultaneously and so it tends to remain at the same place. Consequently, the lower part of the body moves ahead and the upper part is left behind, so the passenger tends to fall backwards.

 

2-When a hanging carpet is beaten with a stick, the  dust particals starts falling out of it, why?


Ans-The reason is that the part of the carpet where the stick strikes, comes in motion at once , while the dust particles settled on its fur, remain in position due to inertia of rest. Thus , the part of the carpet moves ahead with the stick, leaving behind the dust particles which fall down due to the earth’s pull.


3-On shaking the branches of a tree, the fruits fall down , why?


Ans- The reason is that when the stem of the tree are shaken , they come in motion, while the fruits due to inertia, remain in the state of rest . Thus , the  massive and weakly attached fruits get detached from the branches and fall down due to the pull of gravity.

 

4-On striking the coin at the bottom of a pole of carrom coins with a striker, lowest coin only moves away, while the rest of the pole remain intact, why?


Ans-The reason is that as the striker hits the lowest coin, it moves (i.e. changes its state of rest), while the remaining pile due to inertia I rest remains where it is and ultimately takes the place of the original pile due to the  force of gravity.

 

5-When a smooth card placed over the mouth of a tumbler is flicked sharply in the horizontal direction , the card flies away , but the coin kept over the card falls into the tumbler, why?


Ans-The reason is that when the card is flicked , a momentary force acts on the card, so it moves away. But the coin kept on it does not share the motion at once and it remain at its place due to inertia of rest . The coin then falls down into the tumbler due to the pull of gravity.

 

6-When a corridor train suddenly starts, the sliding doors of some compartments may open, why?


Ans-The reason is that the frame of sliding door being in contact with the floor of the train also comes in motion on start of the train, but the sliding door remain in its position due to inertia . thus  the frame moves ahead with the train while door slides opposite to the direction of motion of the train. Thus the door may open.

 

Inertia of motion :


A body in a state of notion, continues to be in the state of motion with the same  speed in the same direction in a straight line unless an external force is applied on it to change its state this property of body is called the inertia of motion.

 

EXPLAIN THE FOLLOWING:


1-A cyclic riding along a level road does not come to rest immediately after he stops pedalling, why?


Ans-The reason is that the bicycle continues to dur to inertia of motion even after the  cyclist stopes applying the force on the pedal. The bicycle comes to rest afterwards as result of the retarding force of friction between the tyres of bicycle and the ground.

 

2-When a passenger jumps out of a moving train, he falls down, why?


Ans-This is so because inside the train, his whole body was in a state of motion with the train . On jumping out of the moving train, as his feet touch the ground, the lower part of his body comes to rest, while the upper part still rrmains in motion due to inertsia o fmotion. As a result , he falls in the direction of motion of the train and gets hurt.

                To avoid falling , as the passenger’s feet touch the ground, he should start running on the ground in the direction of motion of the train for some distance.

 

3-When a running car stops suddenly, the  passenger tends to lean forward, why?


Ans-The reason is that in a running car, the whole bod of the passenger is in the stare o fmotion. When the car stops suddenly, the lower part of his body, being in contact with the car, comes to rest immediately but his upper part remains in the state of motion, due to inertia. Thus his body leans forward.

 

4-An athlete often runs before taking a long jump, why ?


Ans-The reason is that by running he brings his entire body in the state of motion. When the body is in motion. It becomes easier to take a long jump.

 

5-A ball thrown vertically upwards by a person in a moving train comes back to his hand, why ?


Ans-The reason is that at the moment when ball was  thrown, it was in motion along with the person and the train. It remains in the same state of forward motion even during the time the ball remains in air. The person , the time air and  the ball, all move ahead by the inside distance due to inertia and so the ball falls back into his palm on its return.