in one sense we are going to begin and see where physics is really began. And many people believes that physics began at this one moment, when we began to study what is called motion. Because till then it was not really not in physics in the way that we think about it. Physics or science was more philosophical Aristotle would make up some theory. As this is the natural state of objects. And just because we can make it up and we can talk about it its just because it sounds good it’s true, like it is assumed to be proved that my sounds very ridiculous to you right? How can we just take it to be like that? But it was the case until somebody called Galileo began to become what is skeptic and say okay you are telling me certain things shall I try it out let’s see if it works. And that many people will believe was the official beginning of science in the way that we know it. And if somebody says something or somrbody thinks something is true in other words you know the natural state of objects to be in the state of rest, something like that. Then the fact that Galileo took it out there tried it out in the real world so it was really works was according to many people the official beginning of science. And one of the first things that we studied was what we are going to call motion or when something is moving and one of the first things that we are going to try and understand is what is it mean when we say something is moving. Let’s take a very simple definition right? you are looking at something. You continue to be see it, you keep looking it at and if it is there we say that it is at rest ok . But if you see it and after sometime it is not there and you look where is it turn your head and it is there and you have to keep turning your head to make sure you keep seeing it. Then we say the body is moving. Someone like pretty (@1:36 ) so if yiour head turns then it is moving. So what are the first question we will ask that is how do you know that something is moving? And the simple answer is if your head turns . that is one of the fundamental ways we see it great. But what if you are in a train? Right? So who is really moving? You are in the train and somebody is sitting right in front of you and you look at him, he is right there you don’t have to turn your head to keep seeing him of course if somebody is one case is if somebody is left out if somebody is moving away from you in a strait line, that of course you don’t have to turn your head but still know that it is moving because it start become smaller and smaller and smaller or if it comes towards you it become larger and larger and larger and your intuition tells you that it is not the person really growing so fast so (2:16 ) must be coming closer to you. So all this is based on intuition right? As what things moving and what things don’t . so we are in the train we are seeing someone not moving. But are they really not moving? And what is that question really mean? Because if somebody is standing outside he is gonna say that hei hei hei that guy is moving but you are going t sit inside you are not moving okay, let’s take one more example you are in the train and you look outside what you see you see that trees are (2:41 ) the fields are __ you see them all moving right? Are they moving? Or are they at rest? And you are the one who is moving or does that question even make any sense? Because if you look at it if you are sitting here in the earth and you say all these are at rest right now you look at me and you probably think that ok the tablet is at rest and everything is at rest ask an astroner that he will say something else he is gonna to be out there looking at earth rotating really really fast. How fast? The order of thousands of kilometers every yard and he is gonna say that that person really really fast. Because even right now we are moving really really fast.so are we moving or are we not is a pretty difficult think to measure.