00:00so we have a collection of objects in

00:02front of us we have some blue squares we

00:05have some green circles and we have some

00:07yellow circles and let's say I'm

00:09interested in these blue squares I want

00:11to study them closely I want to know

00:13whether they interact with each other

00:15and how they interact with the other

00:17shapes so what if I group them by just

00:20drawing a boundary around these squares

00:23so by doing this what I've done is I

00:25have separated out the portion that I

00:27want to study and now I can think of

00:29this collection which is within the

00:31boundary as a system of objects that I

00:34want to study So within this is the

00:36system this circle here is the boundary

00:39and everything outside this boundary is

00:42let's say what we call surroundings so

00:44what I've done is I've made it a bit

00:46easier to describe this configuration so

00:49this helps set context so let's say you

00:51walk up to your friends and you want to

00:53discuss some thermodynamics with them as

00:54one does of course you want to be able

00:56to easily communicate what is it that

00:59you're interested in and as soon as you

01:00you define a boundary you separate the

01:02part of your interest which is the

01:04system from whatever is not included in

01:06the system that is the surroundings and

01:07again this choice of boundary is

01:09arbitrary so if I say something like my

01:12system has yellow circles I can draw a

01:14boundary around this and everything

01:16within this becomes my system and

01:18everything else which is outside this

01:20becomes my surroundings so if we go back

01:22to our original example which was the

01:24system of blue squares there are some

01:26questions that I can ask about this

01:28boundary can any one of the circles

01:30enter this system or can one of the

01:33squares exit this system and what if

01:35maybe they can't go in or go out

01:37physically but there is some exchange of

01:39energy at this boundary like if you pick

01:41up a glass of hot milk your hands are

01:44touching the glass and not the hot milk

01:46directly but still you feel the heat so

01:48if these blue squares are at a higher

01:49temperature and all of the circles are

01:51at a lower temperature will there be an

01:54energy transfer at this boundary so to

01:56answer these questions we can build on

01:58top of this idea and classify system

02:00systems based on how they interact with

02:02their surroundings let's see how that is

02:04done so to study the interactions

02:06between systems and surroundings let's

02:08take this bottle with some water in it

02:10so in the example we saw before the

02:12boundary was imaginary and arbitrary

02:14here let's take the boundary to be the

02:16outside surface of this bottle so in

02:19this case the boundary is a real

02:20physical boundary and what we are

02:22interested in is across this boundary

02:24whether matter or energy can be

02:26exchanged so in case of this bottle now

02:28because it is an open bottle you can add

02:31more water into it or you can remove

02:33some water from this so we know that in

02:35this case matter can be added or removed

02:38and so an exchange of matter is possible

02:40across the boundary and similarly if we

02:42think of the exchange of energy so if

02:44this water was at a higher temperature

02:46just by touching the surface outside

02:48because of the energy transfer you would

02:50realize that the water is hot which is

02:52why in this case an energy exchange is

02:54also possible so such a system which

02:57allows for the additional removal of

02:58matter or for the exchange of n energy

03:00with its surroundings is called an open

03:02system but now what if I cap this bottle

03:05and now what I've done is I've closed

03:07this bottle so after this I cannot add

03:09more water into it and I cannot take out

03:11water from this so in that case I have

03:14prevented the exchange of matter across

03:16the boundary but still if the water is

03:18hot or cold the outer surface of the

03:20bottle will also be hot or cold and so

03:22even by capping the bottle although

03:25there is no exchange of matter there is

03:26exchange of energy across the boundary

03:28and such a system is called a closed

03:31system but what if I want to prevent the

03:33exchange of matter and energy so let's

03:36say what I do is I coat this bottle or

03:39the surface of the bottle with some

03:41insulating material and now what I'm

03:43doing is because of this insulation I'm

03:46making sure that the energy transfer

03:48across this boundary is also stopped so

03:50what is happening in this case is that

03:52there is no transfer of matter nor there

03:55is a transfer of energy and such a

03:57system is called an isolated system so

03:59you can see that how based on whether

04:01matter or energy can be exchanged we can

04:04classify the systems as open closed or

04:07isolated but I want to bring out a point

04:09here to make the system isolated we

04:11assume that we are quoting this bottle

04:13in some material but usually in real

04:15life we would never find examples like

04:18this and so the point here is that

04:20isolated systems are a hypothetical

04:22construct they sometimes help us

04:24simplify our calculations or remove some

04:27complicated external effects and we can

04:28get good approximations which are useful

04:31and there's one more thing here so it's

04:33easy to identify whether there has been

04:35an exchange of matter like for example

04:37when this bottle was not closed we could

04:40easily see how this would be an open

04:42system because we could add water into

04:44this bottle or or take out water from it

04:46but sometimes when we look at the

04:48exchange of energy it can get tricky so

04:50let's take another example and see this

04:53sometimes when you're trying to identify

04:55whether a system is open or closed or

04:57isolated things may get tricky let's go

05:00through one example and try to

05:01understand this better earlier we had

05:03seen the system of a bottle with some

05:05water in it but now let us look at this

05:08system which is slightly more

05:09complicated looking let me just take you

05:11through all the parts of the system so

05:14here there is a block and this block is

05:16closing off this container which has

05:18some gas inside and you can see that

05:21I've drawn these gas molecules and we

05:23know that they're randomly moving about

05:25within this box but the way I have set

05:27up this container is that I can push on

05:30this block to move it inwards and we'll

05:32assume that there is no friction along

05:34these walls so although the block is

05:36still now at this moment we are going to

05:38assume that we can push the block from

05:40here and it can move downwards and also

05:43inside this chamber along all these

05:45walls let's assume that we have coated

05:48them with some insulating material and

05:51what this does is this insulates all all

05:54the walls of this chamber so what we're

05:56saying is heat cannot be transferred in

05:58or transferred out via these boundaries

06:00or another way to say the same thing is

06:02that this wall or this boundary is

06:04adiabatic so there is no heat coming in

06:06or heat going out so this is the setup

06:09now what we want to find out here is

06:11what type of system is this is this an

06:14open system or a closed system or an

06:16isolated system so to check that we will

06:18look at two things whether the exchange

06:20of matter is possible and whether the

06:22exchange of energy is possible so first

06:24let's look at matter now because this

06:25block is placed here and all of the gas

06:28is contained within this chamber gas

06:30cannot escape from this or more gas

06:32cannot be introduced into the chamber

06:34and so for this system matter exchange

06:36is definitely not possible so we know

06:38that this cannot be an open system

06:40because if matter exchange was allowed

06:42it would be an open system so now let's

06:44look at energy so we know that this

06:46boundary inside the chamber is adiabatic

06:49which means there will be no transfer of

06:51heat across this boundary so if we know

06:53that there will be no heat transfer

06:55across this boundary can we also say

06:57that there will be no energy transfer

06:59across this boundary let's think about

07:01this now we know that this block can be

07:05pushed so what if we push this block

07:07downwards so when we push this block a

07:10part of that mechanical energy went into

07:12moving this block downwards and a part

07:14of it also got transferred to the gas

07:17molecules because we see that the

07:18kinetic energy of the molecules is

07:20increased and they start moving faster

07:22so that means even when there was no

07:25transfer of heat possible across this

07:28boundary energy transfer was still

07:30possible and so because we cannot

07:32exchange matter but energy can be

07:35exchanged we know that this setup is a

07:37closed system and the important point I

07:40want you to remember from this exercise

07:41is that whenever you're checking for

07:43energy transfer you should check for

07:46energy transfer across all forms

07:48including heat and mechanical work