What is Inertia?


Inertia is something that everyone uses but do not understand. In addition, it relates to every object or body at some point.

Furthermore, it is a state of rest or inactivity. In this topic, we will discuss inertia and how it works for the object. Also, in the topic, we will discuss the various properties of it.

Law of Inertia

It refers to the position in which a body repels a change in its position of motion or rest. Moreover, it also includes a change in the direction of an object.

Most noteworthy, the object can keep on moving or stay at rest until and unless it is stopped or moved in a different direction with an external unbalanced force.

Inertia is also known as Sir Isaac Newton’s first law of motion which state that “An object will remain at rest or in its state of uniform motion in a straight line unless it is constrained to change its state by the act of an external force.”


Inertia and Mass

According to Newton’s Second Law, the force (F) on an object is equal to the mass (m) and acceleration (a) of the object. Also, these things are required to change the state of motion of an object. Besides, its formula is:

F = ma

For understanding how a mass of an object relates to it, consider a continuous force. Fe that is acting on two objects or bodies. Among the object, the first body is of mass ma and the second object has a mass of mb.

When the force Fe acts upon object ma and the acceleration is a1. Then

Fe = maa1

When the force (Fe) acts on mass mb and the acceleration is a2.  Then

Fe = mba2

Since Fe remains constant and it does not change in both then:

maa1 = mba2


ma / mb = a2 / a1

Besides, if ma is bigger than mb then a2 will also be bigger than a1 to make both of them equal to Fe and vice versa.

In simple words, the mass of an object is a way to measure its tendency to resist an applied force and continue in the same state as it is now moving or at rest.

Besides, mass and inertia are two completely different things. We use units of mass for measuring it. Furthermore, the unit of measure in the British system is slugs, and in the SI unit, it is gram and kilogram.

Usually, the scientist does not consider it while discussing motion problems. In addition, they discuss the mass of an object.

Moment of Inertia

The rotating bodies also have a tendency to resist forces. But, due to its composition of a collection of particles that are at a distance from the centre of rotation, scientist discuss the moment of inertia relatively than its inertia.

The inertia of a body or object in linear motion is equated according to its mass. But, on the other hand, the inertia of a body in a circular motion is complicated and it depends upon the shape of the body.

Besides, the formula of the generalized expression for the moment of inertia (I) or a rotating body of mass m and radius r is

I = Kmr2

In the formula, K is constant and depends upon the shape of the body. Also, the units of the moment of inertia are (mass) (axis-to-rotation-mass distance)2.

Solved Question for You

Question. Which of the following do we use to measure Inertia of an object?

A. Σ miri2

B. F = ma

C. E = mc2

D. s = d/t

Answer. The correct answer is option B.

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