so in the previous video you have watched miss ellie talk to you about what are base si units and you have me now miss lee okay if you don't know how to spell my name it's here okay so today i'll talk to you about derived units and you already know that hey you know in base si units you have this seven physical quantities and you might be thinking to yourself teacher teacher fake one there are other physical quantities with other si units that i use that is not here how are for example energy power density area momentum time weight mass like which one is base and which one is derived okay so what you need to understand about base si units is that this is a limited list okay so anything that is not on this 7 is not a base si unit unless the scientist decides otherwise and we will then be informed as cool teachers right but right now anything that's not in this seven are not based as i units okay so what do we call them then we call them derive units okay so derived units is a combination and all derived units is combination of the base s i so it will be a combination of the base s i units by multiplication or division it can be n or e division okay so when it comes to derived units right so i'll give you a few examples now example one maybe you'll be thinking about teacher volume symbol is v what is the unit the unit will be so whenever you want to think about units right if let's say you you can't really recall it so i have a few steps that you can roughly want to go through number one recall an equation any equation that you may or may not encounter for example volume can be calculated using let's say x power 3. for example you have a cube and then you multiply the size of the cube but if i want to think about unit now we are going to insert unit so hence the unit or the derived unit okay maybe i should write this as derived the derived unit of v will be meter cubed okay let's do another example let's say for example we talk about force and you symbol f and you might be thinking teacher the si unit for force is newton correct s-i unit not base s-i but s-i unit is newton now that that dude that british do during lockdown who invented calculus one ah newtona all right so si uni is newton but base si unit so when you see the word base or it has to be only the seven anything that's not in the seven is not based as i unit so then you might be thinking to yourself okay how do we make newton to consist of base as i unit we go through the three step again step one equation what is the most most popular equation for force fmao f equal m a uh i use so many time now okay good and then beginning to yourself okay so if f is equal to m a then i can insert unit so i'm going to change color and do the insertion now okay so the unit for newton is equivalent to unit for mass is kg unit for acceleration is meter per second square so this will be equivalent to kg m s negative two okay you might be thinking miss that's the order matter the order doesn't really matter but there's a certain convention where if there's prefix we put in front okay so i'll write that down for you like kg kilo is a prefix so normally prefix in front so here in itself there are a few problems number one you may not know or you may not be able to recall an equation for example f equal to m a is pretty straightforward but maybe let's say you do pass your question and you see a question that you don't know so in those cases there are two possibilities number one maybe your syllabus haven't covered yet number two maybe the question will give you information all right so we will hop on there and do an example but once again just to differentiate the ideas base si unit must consist of the seven quantities only anything that is not in the seven is not a base si unit so the base si unit for force is equal to kg ms negative 2 but the s i unit can be anything in this case it will be newton all right so certain physical quantities have si unit have base si unit certain physical quantities like volume it only has base si unit because there's no point giving volume another unit all right so now we can look at a past year question okay so here is an example this is from fat match 17 paper one two oops will jump okay so it says here which expression has the same as i base unit as pressure so whether you have done ig or other syllabus you probably have already been introduced that pressure symbol p is equal to f over a if you are thinking oh yeah i don't remember a lot of the physics i've left it behind in high school well now is the time to keep uploading i mean it's not saying that you're fallen behind but you just have to chase the grind a bit more okay so pressure is forced per unit area google is your best friend as well so if we want to look at the si based unit of pressure then i see si base unit of pressure means i need to change this to si base unit and compare with all the options abcd so if you remember just now in the example i say f is equal to m e so now i will have m times acceleration over area so hopefully you know lowercase a is for acceleration uppercase a is for area so now i can convert to units base units this will be kg ms negative 2 over m square area 1 okay so right now i can do some simply simplifying a bit so meter per meter square i mean i can take kg and i multiply by actually it's divide right so this as negative 2 this one here can move down right so this will be s square and then this is m over m negative m squared so you'll get m negative 1 m so some basic prefix is needed okay so then i look at this it says here that the base units for pressure is kg meter second square okay so i need to check the numerator of course you have mass on top okay and then you have meter which corresponds to length and then time square not time square kl just second square okay so they will share the same as i base unit you don't have to wonder what this is you see the correct term you match it so in this case the answer would be c let's look at another example which pair of units are not the same when expressed in s i base unit uh now we need to express everything uh miss aryana we need to compare so the only way we can compare si base units is to break all the non-si base unit down to si base unit okay because then we can compare basic to basic okay so this one is okay i don't need to convert anything but here this newton kg negative one i'm just gonna write here this one kg negative one i think to myself newton is false and we've been here before you know the base si unit for newton so i skip a bit of step uh this will be k g m s negative two why because when i jump from here to here i'm using f is equal to m a so after a while you will be able to skip certain steps this is objective so showing the steps doesn't matter okay so then i can put kg ms negative 2 here and i have kg negative 1 here and they will just cancel off each other and then i get m s negative two m s negative two a is good all right let's check the second one so the second one you have newton's second i o okay lah we already know the best as i base s i for newton k g m s negative 2 and then we times s okay the other one i'm going to put blue okay so what do i get i get kg ms negative 1. so you can see kgms negative one kg mass negative one okay this newton is for this one so we're good this is solid okay pascal so when you see pascal hopefully you remember that pascal is the unit for pressure i cheated a bit i got the base si unit for pressure already is here okay all you can derive using the steps i have given just now so the base si unit for pressure is kg meter second negative for two kg meter negative one second negative two but in this case right you could also be a bit aware that this side here is newton hey we don't need to actually use base all the way for both in this case you know that pressure is equal to f over a and the s i unit not base s i but s i unit is newton over meter square okay so this newton is for force you can put newton here and then your meter negative two is for area which is the same as pascal okay so this means uh these are both si units but they are both not base you want the base si unit it will be this one okay teacher then by elimination is d ayala but if you want to just confirm then d actually needs a little bit more work because generally when you do pass your paper right we assume that you've already finished the syllabus and you are ready and you know all the physical quantities that you need to know in your as and you may not it may not be the case now because you know look i'm just a newbie a level kid and i'm just trying to grind my way to some form of mastery i got you so whenever you see something you don't know you can choose to skip or you can confirm your lecturer all right but there's some things that i already know so let me try and see if you also know this for example this v is actually volt you know volt from voltage okay so the unit for volt is actually defined as work done per unit charge so this one is a bit of workload by elimination i know the answer is d but here i need to do a lot of work so this is work done per unit charge okay then i need to times meter negative two but good news you see the newton and coulomb here so i'm gonna steal this as well so i will work on both sides at the same time to prove that they are not the same that's all i want to do or if i'm running out of time i will just circle the correct answer it is the quality these wrong all right but let's say i want to i just want to show so in this case right when you think about work done you should also consider something like force times distance okay so use equations that you already know voltage is work done per unit charge and then work done is force times distance okay so this one is this one and then divide by charge times meter negative 2 or distance square get on my bed i should keep this one as distance negative 2. you see immediately i got some problems already you wanna know what the problem is one over distance squared on this newton per coulomb or newton per coulomb here right i need to think about what is newton newton here is force this newton is false force over charge and then i look at this side i have force over charge here this second and this second block this distance force times distance so if you are not clear force times displacement is work done w equal to fs hopefully you're familiar with this basic equation so displacement and distance can only cancel out one time so this unit will end up being newton per coulomb times meter whereas this one is newton per coulomb so fancy is d low okay so certain one you need to grind a bit or you can use the process of elimination how quickly you do these past year questions depends on your practice all right so go practice to pass your question and i'll see you in the next video where we talk about why should we care if the best base asi unit is the same why should i care pleasurable pascal i don't think support other things are why should i care all right that'll be in the next video and i'll see you in that one