 We now look at some illustrations of thermodynamic systems. We will see a real physical situation and then look at the way we abstract it and come to a final system figure from the point of view of thermodynamics. The first illustration we have here is water inside this bottle. So here we have the photograph of the water inside this bottle and the first thing we do is mark the boundary of the water, you see it in black here. Once you mark the boundary of the water, the region of interest then we can neglect or forget the details of the bottle, the shape, the extraneous things. So this is the boundary of our system and to emphasize that this itself is the boundary of the system. We will generally inlay it the exact boundary with a dotted line. So our system that is water in the bottle is whatever is contained inside this dotted boundary line. Another illustration of a system is air inside the tire of a car. So here we have the picture with all the clutter, the wheel, the connecting bolts, the tire, you do not see the tube inside, you have the structure of the car, part of the mudguard. Okay, the first thing we do is mark the boundary and we can imagine that the air will be in the form of a ring or a torus and here we have the inner radius of the torus and this is the outer surface of the torus. Once we do that, we can now concentrate on the boundary and to get rid of the confusion we inlay it with dotted lines. So you see two sort of circular dotted lines, whatever is the toroidal zone or ring like zone in between is our system. It contains the air which is in this car tire. So here we have a tank and let us say that the contents of the tank are going to be part of our system. Although the tank is meant for nitrogen, it could contain anything. So the first thing we do is draw the outline of the tank. The moment we draw the outline of the tank, we have made the primary boundary, we can forget about the details of the tank. And so this is the system boundary and to emphasize what the system boundary really is, we show it by a dotted line. Again here we notice that we have a passage here and another passage here. One of them could be an inflow passage, one of them could be an outflow passage and if the two passages are not closed, they are open, it will be an open system. If they are closed, then our system will be a closed system. Here is the illustration of a series. It is made up of essentially two main components, a cylinder and a piston and this is the cylinder part where the medicine or whatever is to be injected can be located and through this spout and through a needle which is connected to it, it can be injected into a human animal or whatever it is. Suppose the, just now it contains air but it could contain anything else. So suppose the air inside this syringe is going to be our system. So first what we have done is we have laid out the appropriate boundaries and once you have laid out the appropriate boundaries, the actual physical detail of the syringe we can neglect. So what we see is this cylinder, the hollow part and the piston which we can push in to inject whatever is inside through the spout. Once the content, say in this particular case air inside this cylinder is going to be our system, we will show it by dotted line. So as not to get confused by the other things and now here you will notice something which we will come across in thermodynamics quite often, we have a cylinder and a piston and whatever is contained inside the cylinder is our thermodynamic system. Another illustration which leads to a cylinder piston type of arrangement is a foot pump used to inflate bicycle tires or sometimes even small car tires. So here you see the structure, the pressure gauge, the rod of the piston, this is the cylinder in which the air gets compressed and this is the connecting tube, the other end of which would be connected to the tire. There is a lot of clutter, so the first thing we do is note the boundaries of the components which are of interest, you will see them here sketched in black. Once you do that the next step is of course to remove all the clutter and look at the boundaries and again there is some confusion. So if our system is the air inside this particular foot pump or the cylinder of the foot pump we lay it out with dotted lines. So whatever is inside the dotted line here is the our system, the air inside this. Another illustration is that of a water pump, here you will see in a laboratory situation a centrifugal water pump is driven by a motor which is inside this safety shield. This is the inlet pipe through which the pump sucks in water, this is the exhaust pipe through which the pump throws out water at a high pressure. So the first thing we do is to sketch out the boundaries of the system involved and you will see here the boundaries sketched out in black. Once you do that next thing is to look at the boundary itself and we have a region which could be our system but then let us say that the water inside this pump is going to be our system so we lay it out in the dotted line. So whatever is inside this dotted line that is going to be water and that is our thermodynamic system. You will notice that the motor part in which there is no water present is not part of our thermodynamic system and hence it is not included in the dotted line. We will also notice that water can flow in through this inlet duct and water can flow out through this exhaust duct. So this is an illustration of an open thermodynamic system.