Importance of the Newton’s first law

Discussion helps you to understand a concept better than thinking it one’s own self. I always like to study science with historical continuity which helps me to think in a different way. I got new friends in that journey of different way of scientific discussion. Giving and sharing improved my understanding of physics in a way completely different from text books.

          First I want to talk about the very basic Newton’s three laws.

Law means an abstract from the Nature. You cannot prove it but you can just observe. We don’t know the answer of why to these laws. It is given by the Nature to deduce the Nature.

          A law is something that is followed by Nature itself. And Newton gave us three laws that tell about the movement of objects in real life.

Newton’s first law states that,

          Every object in the universe continues to be in same state of rest or uniform motion until it is acted upon by an external force.

And the second law states that,

          The net external force acting on an object is proportional to change in momentum of that object.

          p – momentum = m*v

m – mass

v – velocity

                            

                                      Fext  = dp /dt

Don’t you think there is a waste here?

          The second law itself is going to give information about the first law as follows,

                  

          When Fext  = 0 it implies p – momentum is a constant.

If mass is constant then “v – velocity” is also a const. The second law itself gives that when there is no net external force acting on a body, the velocity of the object is going to be constant. The constant can be either zero or some finite velocity.

Then why do we need the first law as a separate statement?

Scientist never waste time by writing same thing in two different ways since science is the method of minimum laws. You can suspect the first law but the answer we know.

It has to be something different kind of information should be there in the first law.

         

Let see what it can be?

The answer is there in your bus travel. When you travel in bus near the window seat in constant velocity, you can see through the window, how trees, houses looks moving at constant velocity.

                   

Let assume that the bus window is too small so that you can only see through small holes. You can’t realize whether the bus is moving or the trees are moving.

         

When you suddenly stop, you can see trees and houses and all the things stops moving.

         

With respect to your point of vision, you see all things came to a

sudden halt or stop. But there is no force acting on those things. Then how did these came to a halt.

          If Nature follows only the second rule, then

Fext  = 0 then Velocity should be a constant. But here velocity is changing but without any external force. Does it mean Nature don’t follow Newton's second law?
         

But Newton is very clever. He solved this by simply arguing that, “It is second law. Nature should follow also the first law then only second law would be valid”.

         

          First law says that “No object would change its velocity by itself but will change only when it is acted by net external force”.

          Nature should follow this rule. So Newton formulated a new force called “Pseudo force”.

Pseudo forces are the forces made to explain non inertial reference frames.

He explained that Pseudo force made the trees and house and all the things to stop instantaneously.

          Now you can apply the second law to Pseudo force and it is perfectly applicable.

          Pseudo forces are not only present in the trees and outer environment but also in your bus. If there is an object with low friction with surface is there in your bus, when you accelerate you can see the object moves in the opposite direction to the acceleration. And this was explained by Pseudo forces.  

          Thus we understood the importance of the first law in Newton’s laws of motion.