Hello Welcome to my class Today we shall look at unit 1 and topic is units and dimensions Now we shall start the class with an introduction to physical units and you must note that units are used to express the value and similarities of quantities. Also units gives quantities a dimension. Units gives quantities a face value. Unit of a physical quantity is a randomly chosen standard which is widely accepted by the society and is used as a basis for measuring similar quantities. Now, every measurement has two parts.
The first part is a number, as you can see right here, while the next part is a unit. So in engineering, when you are working with quantities, it is very important to include the units of that quantity. Otherwise, your answer might be marked wrong.
So 30 is the number and meters is the units. So every measurement has two parts, which is the number. and the units now we have some system of units I'll show us some units here number one is the CGS which is the centimeter grand second system we have the fps which is the foot the pound and the second system we have the mks which is the meter kilogram second system we have the mksa which is meter kilogram second ampere unit then we have the british system of units which is the inches and pounds now inches is used to measure length while pounds is used to measure mass now what you are seeing here all these you're seeing here are basic units for this system of units i'll pick that all these in brackets are the basic units for these system of units Now, the system of units that we use today in science and in research is called the SI unit. And for this unit or for this class, we shall be focusing on the SI unit.
And in most of your courses in this semester we shall be using more of the SI unit now I will show some basic SI units that we use in engineering now you must note that the SI unit is called international system of units It is widely recognized and it is being used today in science and in engineering. It consists of seven basic quantities and their corresponding units. I'll be showing us.
in a table some of the basic quantities and the units and also the symbol or units used but before i continue i want us to note that basic units are independent of other units and they are the foundation of which all other quantities can be formed now some examples of basic quantities the first one is mass mass is a basic quantity and the unit for mass is kilogram so kilogram is a basic unit and the symbol or unit for kilogram is kg the next one we have is length the unit for length is meters and the symbol is comma m the next one we have is time so time is a basic quantities and the basic unit for time is seconds the unit is comma x the next basic quantities we have is electric currents i hope you guys know the unit of currents the unit of current is ampere and the symbol is capital a our next basic unit is temperature and the unit is curving in k our next basic quantity we have is intensity of light symbol is candela and unit is CD and we have a next one which is called the quantity of a substance and the unit is mole and the units is M or L so guys these are the basic quantities we have why these are the basic units They are also called fundamental units because they are independent of all other quantities. now we also have what I called the supplementary units just two of them the first one is the radian now radian is used for measuring angles so angle is the basic quantity while radian is the base units then the next one is called the steroid steroidian is for measuring solid angles so these are two supplementary base units that we use in engineering okay now what are the do's and don'ts when writing units now you must never write units in plural forms for instance kilogram is kilogram not kilograms seconds not seconds no so also we don't use full stop or punctuations within or at the end of units and lastly your units should be written either in full or in agreed symbols all right so you don't have to write your units in abbreviations if you must do that it must be in the agreed symbols all right So next we look at what we call the derived units. As you can see, derived units is a combination of two or more of the base units.
In other words, derived quantities are derived from base units. or we can say that derived quantities are formed by adding or multiplying two or more of the same or different base quantities now in the next few minutes i will show us some examples of derived quantities on this table i'll start with area now what is the unit for area is meter squared and the symbol is what m squared if you look at area it's a combination of what's two base units which is meters so it's meters tens meters we got meters squared we have volume so volume is a derived quantity and the unit is what's meter cube which is m cube as you can see volume is a combination of three similar base units so volume is a derived quantity next we have velocity and the unit for velocity is meters per seconds as you can see for velocity it has two base units yes meter which is one we have seconds so is meter per seconds so velocity is a derived quantity next we have acceleration can you tell me the units for acceleration all right so it is meters per second squared here again is a combination of meter and seconds so it's meters per second squared so this slasher means per is meters per second squared so acceleration is a derived quantity the next we have is called angular velocity and the unit is radians per seconds radians per seconds as you can see again it's a combination of two units radians and seconds that is radians per seconds now in our next videos i will tell us why i have been one right here the next is density the unit for density is kilogram per cubic meter here again is a combination of two base units we have the kilogram which is a base unit and we have meters which is also a base unit so density is a derived quantity so the symbol is kilogram kilogram per meters cube i'll give us one more is pressure and the units for pressure is Newton per square meter as you can see again this is a mixture or a combination of two or more base units and the symbol is kilogram per meter per second squared this is obviously a derived quantity so what you are seeing here are all derived quantities while these are the derived units i want you to to list for me two at least two derived quantities that you can think of in the comment box below as i was saying derived quantities are formed by combination of two or more of the same or different base units