Inertia and Momentum

Inertia:

It is the tendency of a body to maintain its state of rest or a uniform motion unless it is acted upon by some external force. It only depends on mass.

i.e.     Larger the mass large will be the inertia.

The property of a body due to which it remains or tends to remain in the state of rest or uniform motion in a straight line unless an unbalanced forces act on it is called inertia. Only unbalanced force can change the state of rest to the state of motion and vice versa. Inertia may show itself in any of the following three forms: inertia of rest, the inertia of motion and inertia of direction.

Inertia of rest

It is the property of the body by virtue of which it remains or tends to remain in the state of rest unless an unbalanced force acts on it. Examples:

• When the bus suddenly starts people in a bus jerks backwards in the bus as the lower parts of our body also sets into the motion with the bus but the upper parts tend to remain at rest due to the inertia of rest.
• When a blanket is given a sudden jerk, the dust particle falls off as blanket sets in motion but dust particles tend to remain at rest due to the inertia of rest.

Inertia of Motion

It is the property of a body by virtue of which it remains are tends to remain in the state of uniform motion in a straight line unless unbalanced forces act on it. Examples:

• When the bus suddenly stops people in a bus jerks forwards in the bus as the lower parts of our body comes to rest with the bus but the upper parts tend to remain in motion due to the inertia of motion.
• A coin thrown vertically upwards in moving bus comes back in the hands of a thrower because the coin continues to move with the bus. This is due to the inertia of motion.

Inertia of direction

It is the property of a body by virtue of which it maintains or tends to maintain its direction of motion unless unbalanced forces act on it. Examples:

• When a running bus suddenly takes a turn, passengers experiences a jerk in the outward direction as the passenger tends to maintain their original direction of motion due to the inertia of direction.
• When the wheel rotates at a high speed, the mud sticking to the wheel flies off tangentially. This is due to the inertia of direction.

Momentum

Momentum is the product of the mass and velocity of an object. It is a vector quantity. The momentum of a system is the vector sum of the momenta of the objects which make up the system. If the system is an isolated system, then the momentum of the system is a constant of the motion and subject to the principle of conservation of momentum.The symbol of momentum is p and its SI unit for momentum is kg m/s.
Momentum of a body is calculated by the given formula,

p = m \(\times\) v

where,
p = momentum
m = mass
v = velocity

The differences between inertia and momentum are as follows:

Inertia	Momentum
It cannot be calculated by using formulae.	It can be calculated by using formulae.
Inertia doesn’t have to be conserved in any case.	Momentum is conserved in some cases.
The inertia comes only in one form.	Momentum comes in the forms of linear momentum and angular momentum
The property of a body due to which it remains or tends to remain in the state of rest are uniform motion in a straight line unless an unbalanced forces act on it is called inertia.	Momentum is the product of mass and velocity.