Now this brings us to the meet of our chapter which is really ask in the question what is sound. So if you want to think of sound as something that travels in the air and reaches your ears, you are right. Now we are going to go in to it deeply and ask the question what exactly is sound. So let’s begin. Let’s take a guitar and let’s pluck one of the string and observe what happens here. what you observe? What looks like that? What looks like really fast oscillation? if you want to slow things down right look at what you see you begin o observe that the strings goes outwards and reaches a maximum point. And when it does that what does it do? there is air all around this little string here in this case it goes that we press air together in other words there is a higher density of air in that little pocket. Next to the string as you can see from what you observe there is a high pressure, from your understanding of pressure from previous chapters you know that there is a higher pressure there. Now what happens to the string immediately? The string is gonna come back. When it does that what is what is really doing it’s a kind of pulling here behind it it push some air and come back now which means that in this gap it is going to be lesser which low pressure so in one up and down, what the string is really doing is compress the air and is brought back and it is kept a little bit of air less for some time, so high pressure, low pressure. Now what is the string gonna do again it is gonna create this again. But even if it does not do that this high pressure area in other words air push in that way what does it going to do? It is gonna try and push the air in other side of it even more. Right? So this compression is going to push little bit more in that side and that is going to little more in the other side this in other words compression is going to travel along with (@1:43 ) following it. right? in other words you push some air that all these balls of air like each other become closely packed again the area again the next area zone as you can see.so in other words what begin to happen what is that this compression almost like that it starts moving through the air I am showing it in one line but you know that is happening all the circle around because air starts moving I all the possible direction. It starts getting compressed and (@2:9 ) in all possible directions. So hter is one compression and one (@2 :13 ) travelling all the possible directions.