 So, having understood about the definition of fluids and having also understood about the compressibility factor about liquids and gases, let us now try to know more about liquids and gases. Now, let us come to gases of the fluid that we call gases and liquids, let us see first gases and then we will come to liquids. Let us see some features for gases, gases as we all know we have got ideal gases which basically obey ideal gas law and the ideal gas law is simple equation of state which is pv is equal to RT. When I say that they obey simple equation of state, they also obey the basic laws of the gas which is Boyle's law which say pv is equal to constant when temperature is constant then we got a Charles law and also we got a Joule's law when we say thermal energy is a function of temperature only. These are very simple gas laws based on this simple gas law we have got a simple equation of state for gas and for any given pressure and temperature condition I can know all the properties of these gases. So, once I know that a particular thermodynamic state space is at a particular pressure and temperature I will know all the properties of that system. Now, if I go away from ideality I will have real gases at very high pressure at very low temperatures and let us see real gases they do not obey the ideal gas law that is what we know and therefore what they have is real gas law or we have complex equation of state. What we had earlier was a simple equation of state and there are various complex questions of state now, we got van der Waals, we got a Bethelert, we got Redlich-Kwong, Bitti-Bridgeman, BWR, Strobe-Riege, Virial. So, there are several equations of state which actually connect the properties of real gases. So, again as I said for ideal gases if I know the pressure and temperature I can get all the properties of the gases similarly even if the gas is now real gas it is away from ideality still using this real gas equation I can again complete all the properties of those gases in spite of the fact that the gas happens to be a real gas. Now, let us go to liquids for liquids unfortunately we do not have any equation of state so for the gases I can complete all the properties using equation for ideal gas law or real gas law I do not have any such equation of state available for liquids and this is a very important difference between these two fluids the gases and the liquids. So, how do I get properties of the liquids if I know at least a few properties of separation and temperature how will I get other properties like specific volume density etc. So, what do I have I do I conduct lot of experiments so it is a very important for liquids I do not have any equation of state and therefore what I have got is basically experimental data. So, I conduct experiments at various important points important pressures important temperatures and acquire data at those points. So, I may do something for example for water 0 degree centigrade 100 degree centigrade some important you know temperatures and pressures 1 bar atmospheric pressure 10 bar etc. and get all the property data at those points. Once I get those points I can then have intermediate values using property relations in thermodynamics we have got several property relations that are available Maxwell property relations for example using such property relations and using this experimental data point I can get approximate data for other points also by using some interpolation etc. For experiments I do I can get more data but I cannot do experiment at all the points. So, the important difference between the gases and the liquid is here I have to conduct lot of experiments in order to get more realistic data while in gases I need not do experiments I have got equations of state over there with this background after understanding the difference between the gases and liquids as this is an introductory lecture I would just like to show different applications of fluids in engineering we have got in mechanical engineering specifically we have got several applications of fluids and when I say fluids I am referring to gases and liquids. So, various applications are in automobile what we have is a petrol or diesel aircraft again we have got a fuel spacecraft again we have got a fuel which could be in liquid form which could be in gases form also. Also we have got air compressors we have got steam turbine we have got electric water pump alright. So, these are all various major engineering applications in mechanical engineering which actually solely depends on fluids and therefore they will be governed by the properties of the fluid. If I want to design a compressor I need to know the properties of the fluid properties of the air at those pressures and temperatures for which I am designing and this is what for we should know all the applications of the fluids because our devices are going to be designed for those property data. Similarly, we have got refrigerator where refrigerant is also it could be in liquid form it could be in gases form then we have got nitrogen diva where liquid nitrogen could be stored we have got a helium balloon we have got air conditioner where refrigerant again plays a very important role these are different applications of fluids that we come across in mechanical engineering and if you want to design these devices we have to know the properties of the fluids at different pressures and temperatures and therefore this topic has its importance from this design perspective of various devices. So what have we learnt in this introductory talk we have understood that liquids and gases can flow and that is why they are called as fluid or the fluid definition is basically because of the fact that liquid and gases can flow while solids cannot flow and therefore they are not qualified to be called as fluid gases are compressible while liquids and solids are assumed to be incompressible. We have also seen about the difference between ideal the gases and the liquids the ideal and real gases we have got equation of state while for liquids we do not have equations of state available and with what we also saw was different applications of engineering fluids.