Newton's First Law of Motion

Newton's first law of motion simply states that :- A body at rest will remain at rest and a body moving with constant speed will continue to move with constant speed in a straight line until and unless an unbalanced external force is applied to it.

Let's analyze it properly now.

GOALS:-

⟶Basic understanding of first law using examples and illustrations.

⟶Relating that to real life scenarios.

⟶Understanding balanced and unbalanced forces.

⟶Brief discussion on inertia.

⟶Summing up our discussion and what to take away from this article.

Newton's first law with examples and illustrations:-

Newton's first law is very fundamental and easy to understand if you are able to relate it physically. Take for example a scenario, you are lying on the bed with your phone for a long time, you will lie there until and unless your mom comes and forces you to study, at least if you aren't an absolute nerd like me. Here, you lying down with your phone is the state of rest and your mom forcing you to study signifies the external force required to change your state of rest. Similarly a ball at rest, will be at rest until and unless you apply an unbalanced force on it. Now what's an unbalanced force, we'll come to that very soon.

Now lets take another example, you are playing a video game, you will continue to play the video game the way you are until an external agency affects you. Let me explain. You are playing and your friends come in, this will affect you to play the game more rigorously. On the other hand if your mom comes in, you have to stop or at least slow down. Or say you are playing GTA and your friends come in and most of them like to play Counter Strike. Now this will change the game that you are playing.

Similarly a ball rolling with constant velocity will keep on rolling with the same velocity until and unless an unbalanced force is acted upon it. This may turn out to be a little tricky because it's pretty difficult to imagine in real life. You may argue that a ball rolling with constant velocity eventually comes to rest without us doing anything or applying any force to the ball. It seems like there is no force acting on the ball but in reality there is a force of friction acting on it that we tend to ignore.

Now if the frictional force was absent then no net force will be acting on the body. In that case the body will keep moving with the same velocity. Similarly just like u changed what game you were playing because your friends forced you to do so, here the ball will keep moving in a straight line and will change its direction only if some net force is acting on it.

So now let's gather all the ideas that we've learned and try to summarize what exactly is the first law of motion. So in both the examples we saw two cases. In one case the body was at rest, and in the other case it was in uniform motion. In both of the cases we saw that a force was necessary to cause a change in the state of the body whether it is the state of rest or motion. We can say that the bodies were at a state of equilibrium or balance which was disrupted by our very dear force. The two cases of rest and uniform motion can also be defined as static and dynamic equilibrium respectively.

So, now comes the important significance of the first law which I learnt recently from my teacher and it's very cool. We can say that we have officially defined force as a thing that causes change, in very simple words. Or we can say that Newton's first law of motion defines force.

Balanced and Unbalanced forces:-

Now that we are done with our basic explanation of force we should try to see what the unbalanced force is all about that we kept mentioning throughout. Imagine playing tug of war with a friend who has equal strength as you. The rope will be constant and none of you will win. But if you are playing tug of war with a sumo wrestler then its obvious that he'll pull the rope towards him and you will lose. In the first case the forces were equal and opposite and they cancelled out each other or balanced each other. Therefore there was no net motion. But in the other case the sumo wrestler overpowered you or the forces were unbalanced which caused net motion. From this example we can easily say why we told that unbalanced force is required to change the state of a body.

In all the examples of the rolling ball that we considered you may ask why we ignored gravity of did we assume it to be zero just like friction. The answer is that gravitational force acts on the ball throughout, but the force is balanced by Normal reaction by the surface or ground, which we'll discuss in detail in near future. Basically Normal reaction acts in the opposite direction of the gravitational force or its weight and cancels it out, which makes them balanced forces.

What is Inertia and why the first law is commonly known as the law of inertia??

Now that we have the basic idea of the first law we can easily define inertia now. The simple definition of inertia is the tendency to remain unchanged. Or as we say in physics that it is the tendency to remain in the state of rest or uniform motion. And that statement looks very familiar to us because that's exactly what we mentioned in the first law so far. Also Inertia has various types which we can easily relate to our above explanation. The types of inertia are:-

Inertia of rest:- The tendency of a body to remain at rest

Inertia of motion:-The tendency of as body to remain in the state of uniform motion

Inertia of direction:-The tendency of a body to move in a straight line

It can be easily understood now why the first law of motion is also known as the law of inertia.

One line summary and what to take away from this article:-

Now that the blabbering and chit chat is done. We can simply say that Newton's first law of motion says that until an external unbalanced force acts on the body it will continue to do whatever it is doing. As simple as that.

Well, there are still many things to discuss related to this topic like inertia vs mass and so on. But the article is already too long so we are going to conclude here as of now. See you in the next one. Next time we'll be discussing about the 2nd law of motion. So do follow to get the notification.

I was heavily inspired by this video of "don't memorize" on the same topic, check it out for quick reference, it's good.