The True Meaning of Inertia


The word inertia is the most misunderstood term in schools. Teachers teach them as a term and never have given the accurate definition of what inertia is. Here is an intuitive approach to help you understand inertia.

Before I explain to you about inertia, it will be helpful if I explain you the difference between weight and mass.


Mass is the amount of matter in an object. Let us consider an object like an iron ball for examples here. The molecules in it are densely packed and the total amount of these molecules are 100 kg. Now this is the mass of that particular ball and it is a constant one. When you take the ball to the outer space, the mass never changes.


The weight, on the contrary, changes from planet to planet. It becomes zero when taken to outer space. From what we learned in school about Newton’s second law, weight simply means mass times the acceleration due to gravity. The 100 kg ball on earth will weigh (100 x 9.8) 980 N. Earth’s acceleration due to gravity is 9.8 m/s. Mars’s acceleration due to gravity is 3.8 m/s (Microsoft Encarta 2005). The same ball on Mars would weigh (100 x 3.8) 380 N.


Let me remind you about Newton’s first law. An object will remain at rest or move with a constant velocity unless acted upon by an unbalanced force. This is also called as the law of inertia. So what is inertia?

We could explain inertia as the tendency or natural property of an object to stay at rest or stay in a constant motion. It is the resistance to its change of state of motion. Take the iron ball for example. It will be very hard to move a 100 kg ball. Remember, it is always about mass when it comes to inertia. More mass an object has, the higher the inertia is.

Bottom line

Inertia is a natural resistance of an object to resist any change in its motion or rest.

I was never told of this. Only when I was reading some Encarta page, I came to realize the true meaning of inertia. I am glad to explain this and clarify this finally. Please mail this article to your friends to help them out.

This post was first published on May 20, 2005.

Karthikeyan KC

Aeronautical Engineer, Science Fiction Author, Gamer, and an Explorer. I am the creator of Geekswipe. I love writing about Physics and Astronomy. I am now creating Swyde.

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