Law of Inertia Science: Definition | What Does Inertia Mean | Examples

Law of Inertia Science: Remember physics is all about how things move and why things move. It was Sir Isaac Newton who discovered the three laws of motion. He was a scientist who lived from 1642 to 1727.

Law of Inertia Definition

Let's first learn about the first law of motion. It is also called the law of inertia.

It states objects will remain at rest or in uniform motion in a straight line unless acted upon by an external unbalanced force.

To understand Newton's first law completely. We need to learn about inertia first.

What Does Inertia Mean?

See a very large sofa what's special about it. It's stable it is not moving. Now go ahead and try to move it. The sofa itself is not willing to move. You can't move it. As it is very large. It means you had to put a huge effort.

Now try to move a small stone. You can move it a little bit easier.  It means you had to put a small effort. It was also like it didn't want to move from its original position. Even the smaller things don't want to change their positions. They don't want to move. Even a small stone takes some effort to move.
So, what does inertia means?

 It is the inability of an object to move or stop itself unless external force applied.
In simple terms,

More Weight Means More Inertia.

This is the first rule of physics things like to stay where they are.

What is Law of Inertia?

No object in this universe would start moving unless some external effort is put on it.

It's like all things in the world are lazy. Now the question is if things are lazy and they don't want to move. Then how does the movement happen?

The answer is that there are so many things in the universe which push and pull other things and force them to shift their positions. Like you force the small stone to move.  But as we said earlier, that things are lazy they would try and stop their movement as soon as the effort was removed.

Well, you'll be wrong if you think like that. You'd find it very strange to accept that.

When a small stone was still. It wanted to stay still and once you'd put it in motion after putting some effort it would like to keep on moving. In reality, it would keep on moving forever and ever. But somehow it stops but it stops not because it wants to stop. It stops moving because things in its path force it to stop. It may be due to air or if it bumps into a tree or rough surface on the ground.
Suppose there were no trees on its way, where there was no roughness on the surface, and also imagine that it does not have poles or trees in its way. The stone would never stop. It would keep on moving.

It happens in outer space where there's no air or roughness. If you kick a small stone it keep on moving and moving and would never stop.

So, How can we say that things are lazy?

See the small stone wanted to move forever. But it was stopped by the resistance of air trees or roughness of the surface. It's like you moving on a slippery road you'd keep on moving unless there was some effort put in to stop.
Same is true with a small stone in outer space. It would keep moving as nothing came in its way. It also doesn't want to stop as it is too lazy to do that.

So, now we can change the first rule of physics.

• Things want to stay in the position they are.
• Things want to keep doing what they are already doing.

If things are at rest they want to stay at rest. And if things are moving they want to keep moving.  In other words, things are lazy. So, there's a lot of laziness in the universe.
Physicists have a special name for this laziness it is known as inertia.

Law of inertia Examples

• Shake the branch of a tree, fall off the leaves.
• Fall of rider backward.
• An Athlete often runs before taking a long jump.
• Dust particles on a carpet fall when beaten with a stick is another example for the of inertia at rest.
• A car continues to move forward even its engine has stopped.

 So, now you understand Newton's first law of motion.