Class 9, Science, Chapter-8, Lecture-1, Inertia (Notes)
FORCE:
An external influence which when acting on a body, changes or tends to change its state of rest or motion in a straight line.
Force is a VECTOR quantity
S. I. Unit of force : newton ( N )
POINT OF APPLICATION OF FORCE:
The point in a body at which applied force is exerted, is called the point of application of force.
LINE OF APPLICATION OF FORCE
The straight line through the point of application of force in the direction of force is called the line of force.
BALANCED FORCES:
A number of forces acting on a body which do not produce any change in state of rest or uniform motion or direction of motion are called Balanced Forces.
CONDITION FOR TWO FORCES TO BE BALANCED
- Forces must be equal and opposite in direction.
- They must have same line of action of force,
Effect of Balanced Forces: Change in shape
UNBALANCED FORCES:
A number of forces acting on a body which produce some change in state of rest or uniform motion or direction of motion are called unbalanced forces.
Effect of Unbalanced Forces: Change in state of rest or motion
GALILEO’S LAW OF INERTIA:
“A body continues to be in a state of rest or of uniform motion along a straight line unless an external unbalanced force acts upon it.”
NEWTON’S FIRST LAW OF MOTION:
“A body continues to be in a state of rest or of uniform motion along a straight line unless an external unbalanced force acts upon it.”
INERTIA:
The property of a body due to which it resists a change in its state of rest or of uniform motion is termed as inertia.
Three Types:
- Inertia of Rest
- Inertia of Motion
- Inertia of Direction.
If a moving bus stops suddenly, passengers fall in the forward direction.
Reason:
When bus stops suddenly, the lower part of the passengers which is in contact with the bus comes to rest along with the bus.
But the upper part of the passengers remain in state of motion due to inertia of motion.
If a bus accelerates suddenly from rest, passengers fall in the backward direction.
Reason:
When bus accelerates suddenly from rest, the lower part of the passengers which is in contact with the bus comes in motion along with the bus.
But the upper parts of the passengers remain in state of rest due to inertia of rest.
If a moving bus accelerates suddenly, passengers fall in the backward direction.
Reason:
When bus accelerates suddenly, the lower part of the passengers which is in contact with the bus changes state of motion and accelerates along with the bus.
But the upper parts of the passengers remain in state of uniform motion due to inertia of motion.