 Hello and welcome to another session on physics guys and we are going to start a new topic today and this topic is Newton's laws of motion. Now so far we learned about kinematics where we learned about how things move basically in terms of the description of motion in terms of their position, velocities, speed, displacement, distance, acceleration and all that right. So in the topic which was kinematics we were concerned only about the effect of motion that is how motion is happening and you know we never cared about what is the cause of that motion actually. But in this chapter that is in Newton's laws of motion we will now talk about how or why is that acceleration taking place in the first place. So as of you know Sir Isaac Newton was the first person who actually codified everything or basically he came up with a mathematical explanation to the laws of motion. He carried on with the work of Galileo Galilei and then he himself proposed three laws of motion and his very famous book called Principia Mathematica was what and where all these laws are mentioned. So you are aware of what Newton was going through basically he was amazed by the fact that why the moon is stuck in the space while everything which is thrown up comes down. So that started the process and we have heard of stories that an apple fell on his head and all those stories where he got inspired by that event and all that. We are not very sure whether that event took place but definitely he came up with a very good book at a very early stage of his life very early age actually and that book then revolutionized many things later. In fact the industrial revolution so to say also pose some bit of its existence and evolution because of these you know the laws and the concepts which Newton gave. So anyway so before we take up the Newton's laws of motion we must understand the concept of force. So what is force and how force is the center point of Newton's laws of motion. So we already are aware what force is in a very general term. So you would have seen let's say when you want to when you get up in the morning you open the door of your room or let's say when you close the door or when you switch on the lights then you press the button on the on the on the switch switch panel then there are multiple other you know instances in your life in a day to day life where you feel that force or where you apply force or some force is being applied on to you. So for example you all know that we are getting attracted towards the earth and the earth is holding us at the surface so that's some force. Then when you push something let's say you are driving a cart from one point to the other point that is a push when you pulling for example when you are playing tug-of-war then you are pulling the opponent team so that's a pull then you know let's say the rocket launching when the rocket is getting launched then so such a heavy rocket which is like in multiple thousands of kilos and that is being lifted from the ground so must be there must be some very huge amount of force which is required something is required to live that right when that is what we are going to investigate in these sessions and similarly when the rocket comes back or let's say the aircraft comes back to the earth and then it has to be slowed down or a plane while it is landing it has to be slowed down then again how does it come to rest that's again we would like to investigate let's say something freely falling from sky to the ground rain for that matter so rain is coming down why does it come down what is attracting it towards the earth and let's say while you are playing football so you kick to the football and the football starts moving in one particular direction and finally you score a goal so how does all this happen and for that we are going to learn about force so force is prevalent in our day-to-day life all of us know everywhere if the force doesn't exist then probably our life on earth becomes difficult so we are going to study force so force basically deserves some bit of attention from our side so let's begin so what is a what is for so we describe force as an agent of an agent force is an agent something so I'm calling it an agent force is an agent agent of what so you can ask an agent what kind of an agent what does it do so agent is some something or someone who's doing some activity so what is that agent this agent brings about change okay so agent of change but then you'll ask what kind of change you are talking about so we talk about change in change in these things so let's say it's a state of rest so in the previous chapter we talked about what is rest then we also talked about let's say you know so change of rest or state of state of uniform motion so we talked about what is uniform motion so all of you know that uniform motion is when the velocity stays constant isn't it so constant velocity direction as well as magnitude of velocity must be same so I'm just writing in shorthand constant okay so constant velocity constant velocity right so these are the two these are the states sorry this point is B isn't it and then C let's say direction okay it can change the direction of motion okay and what else it can also change the shape and size is it shape and size okay so what is force force is an agent agent of what agent of change change of what change of either the state of rest for example rocket launching so when the rocket is you know standing at the launch pad and then you lift it up that is what we so there must be some force which is required to lift it up that is we change we are changing the state of rest of the rocket then state of uniform motion let's say a plane was flying and then it has to be it has to land and then and eventually it has to stop so hence from the state of uniform motion gets changed get you know impacted so again that is where you need some force there as well direction of motion so let's say a rain fall is happening there is rain and at at the same time the wind is blowing so the rain which was falling in this direction will get impacted by the wind and hence you will see a deflection in the rainfall and this is a very common phenomena that that happens so direction of motion also is changing and for that matter when you are when you are let's say encountering or you are you know going through a circular motion so let's say this is the you know this is a track where you are going in circular motion so here also if you see every moment your direction of motion is changing so for that also we require some bit of force how to change the you know direction of motion and then last is shape and size shape and size so you know let's say if you have a balloon you inflate the balloon so from no size it occupies some space so you can say that the balloon has occupied some space if you are let's say you know you are making some bread then you are kneading the dough so there also you are changing the shape and size of the dough so hence force is all required for all these activities so this is about force so hence now I believe you you understood what force is so force is basically an agent of change change of what so either of state of rest state of uniform motion of direction of motion or shape and size of the object will take everything one by one now now just to add here this these things are called or let's say these attributes which I have mentioned as point a b c and b they actually together are called state of inertia inertia state of inertia so inertia is off you know so inertia could be of multiple things but generally speaking so inertia off let's say oh for that matter what is the you know how does this word or what does this word mean so inert you might have must have heard of this word inert inert means something which is not reactive so inert metal you would have heard of inert elements and all that in chemistry so basically inertia is resistance the meaning is resistance to change okay resistance to change so something which resists changing change has inertia into so for example inertia off of inertia can be of multiple varieties so for example inertia of rest meaning something which is at rest doesn't want to be changed for example when you are sitting comfortably somewhere you don't want to be moved from that place that's your inertia of you know rest so you don't want to be displaced inertia of uniform motion something is you know happily moving in one particular direction for example a train which is moving on a track at a you know uniform with let's say a motion at a constant velocity then to to to bring it to a halt you need to right apply brakes so hence if until unless the brakes are applied the train is going to continue with its uniform motion so it has that inertia that resistance to come to a halt so hence we say that is that is inertia of motion right now similarly there there will be inertia of direction of motion as well so no one wants to change its direction of motion until you know some external agent acts on it so something let's say water is flowing so let's say there is river there is river which is flowing down right so it will continue to move in one particular direction until let's say you create a dam and then stop the motion or you create a channel or a distributor and and you know allow the water to you know or force the water or you know compel the water to go in one particular direction so hence you require some kind of a force so hence let's say if you are designing some kind of you know embankment such that water comes and strikes this and then changes the direction okay so that's that's again you know so until this embankment is there water will not flow in that direction so that's we say that water has inertia to change its direction of motion similarly you will try to change the you know if you try to you know change the shape of anything or the size of anything inertia you will have to do some activity or some some work on it isn't it you will not be able to see something changing its shape on its own that's what we say that everything will have a resistance to change for example you have let's say a vegetable potato tomato something like that and you want to cut into small pieces then you have to you know use your knife and apply some pressure on the knife to cut it right so hence basically the the vegetable we are cutting is resisting or you know offering some resistance to change hence you would you would realize or you would have realized that you know every now and then if the knife becomes blunt then you have to exert more force to chop the same vegetable right so all these are somewhere indicating that everything in this universe has some inertia or resistance you know so whatever state it is in whether it is of rest or a uniform motion or moving in one particular direction or having one fixed shape it will try inherently to resist any change being caused on to that so that's what is called state of inertia so I hope you understood this word inertia and the entire dynamics which we are going to study now Newton's laws and you know and its implications and applications this inertia is going to you know pay we have to pay a lot of importance or attention to this concept of inertia so everywhere whenever force is being applied it is going to change one of the state elements of the state of inertia and that's how we need to understand how how Newton's laws came into being describing and you know the state of inertia of various objects and hence how we can derive some results from that so that's what will be the you know the next set of discussions which we are going to do I hope you understood it in the next session let's take up some examples where we talk about how force is changing the state of rest state of uniform motion state of direction of motion and shape and size