Physics Lesson 4.5.2 - The Meaning of Inertia

Please provide a rating, it takes seconds and helps us to keep this resource free for all to use

Welcome to our Physics lesson on The Meaning of Inertia, this is the second lesson of our suite of physics lessons covering the topic of Newton's First Law of Motion. The Meaning of Inertia, you can find links to the other lessons within this tutorial and access additional physics learning resources below this lesson.

The Meaning of Inertia

One of the conclusions drawn by observing the Newton's First Law of Motion, is that all objects tend to preserve their previous state of motion. This property is known as Inertia. Thus, we say an object is very inert if we have difficulty in changing its actual state of motion. Let's illustrate this point with some examples.

1. An avalanche is very dangerous as it takes away everything on its way during its downhill motion. Therefore, we say an avalanche is very inert as it is quite impossible to stop it. Indeed, may people have died when an avalanche has taken them away when moving at snowy mountains.
2. It is very easy to make a balloon move and also to stop it when it is moving. Therefore, we say the balloon is not very inert.
3. When you are standing inside a bus and it immediately stops, your equilibrium is distorted as for few seconds you move in the previous direction of bus motion. This occurs because your body possesses some inertia and therefore, it tends to preserve its previous state of motion. The same thing occurs when the bus starts moving immediately. In this case, your body goes backward as it tries to stay at rest as it was before.

From the above examples, it is clear that inertia is a quantity related to the mass of objects. Thus, greater the mass of an object, higher its inertia, i.e. the tendency to preserve the previous state of motion.

In fact, scientifically, the mass is identified and defined through the concept of inertia. We have given a definition regarding mass in the Physics tutorial "Length, Mass and Time. Dimensional Analysis" where it was stated that "Mass is the quantity of matter a body contains". However, this definition is not scientifically correct, i.e. it is a very simplified definition of mass, which interferes with the scientific definition of the quantity of matter measured in mole (remember, mole is a fundamental SI unit). Therefore, the definition of mass provided in in the abovementioned tutorial represents a simplified version, used for an easy understanding of this physical quantity.

In scientific terms, we say, Mass represents a quantitative measure of Inertia, which is a fundamental property of all matter. Therefore, a 100 kg object is 100 times more inert than a 1 kg object as it is 100 times more difficult to make a 100 kg object move (or stop when it is moving) than a 1 kg one.

Example 2

Which of the objects or situations written inside the brackets is more appropriate for the required action?

1. To keep a door opened when there is a lot of wind blowing (barbell, chair)
2. To score a goal with your own head during a football match (bowling ball, soccer ball)
3. To drink a coffee during a trip (inside a moving car, while walking)
4. To stop a downhill moving car when its brakes are not working (one man using his own hands, four men using a fishing net)

Solution 2

1. The action (keeping a door opened) requires a high inertia to avoid the door's crash because of the wind. Therefore, a barbell is more appropriate than a chair for this purpose, as the barbell is heavier and is more helpful in keeping the door in the actual position.
2. Bowling ball is too heavy (massive) than soccer ball, i.e. it has a very high inertia. Therefore, it is not suitable to make a header with a bowling ball as it may cause harm on your head. Soccer ball is better in this regard.
3. It is better do drink a coffee while walking than while travelling in car because you walk at low velocity and in case of stoppage, the coffee doesn't spill out of the cup, unlike in the car.
4. When a car is moving downhill in an uncontrollable manner, it is better to avoid staying on its way, especially when there is only one person who is trying to stop the car. You must try to gather as many people as possible instead and try to make a soft stop of the car through a fishing net or anything similar, to avoid damages caused by the car's high inertia.

You have reached the end of Physics lesson 4.5.2 The Meaning of Inertia. There are 2 lessons in this physics tutorial covering Newton's First Law of Motion. The Meaning of Inertia, you can access all the lessons from this tutorial below.

More Newton's First Law of Motion. The Meaning of Inertia Lessons and Learning Resources

Whats next?

Enjoy the "The Meaning of Inertia" physics lesson? People who liked the "Newton's First Law of Motion. The Meaning of Inertia lesson found the following resources useful:

1. Inertia Feedback. Helps other - Leave a rating for this inertia (see below)
2. Dynamics Physics tutorial: Newton's First Law of Motion. The Meaning of Inertia. Read the Newton's First Law of Motion. The Meaning of Inertia physics tutorial and build your physics knowledge of Dynamics
3. Dynamics Revision Notes: Newton's First Law of Motion. The Meaning of Inertia. Print the notes so you can revise the key points covered in the physics tutorial for Newton's First Law of Motion. The Meaning of Inertia
4. Dynamics Practice Questions: Newton's First Law of Motion. The Meaning of Inertia. Test and improve your knowledge of Newton's First Law of Motion. The Meaning of Inertia with example questins and answers
5. Check your calculations for Dynamics questions with our excellent Dynamics calculators which contain full equations and calculations clearly displayed line by line. See the Dynamics Calculators by iCalculator™ below.
6. Continuing learning dynamics - read our next physics tutorial: Newton's Second Law of Motion

Help others Learning Physics just like you

Please provide a rating, it takes seconds and helps us to keep this resource free for all to use

We hope you found this Physics lesson "Newton's First Law of Motion. The Meaning of Inertia" useful. If you did it would be great if you could spare the time to rate this physics lesson (simply click on the number of stars that match your assessment of this physics learning aide) and/or share on social media, this helps us identify popular tutorials and calculators and expand our free learning resources to support our users around the world have free access to expand their knowledge of physics and other disciplines.

Dynamics Calculators by iCalculator™

• Force Calculator
• Uniform Motion Calculator
• Uniformerly Accelerated Decelerated Motion Calculator
• Projectile Motion Calculator