Today our topic is Practical units for measurements.

Because you must know the basic concept of measurement system.

Which you may not be knowing before, So clear your concept about all types of measurement.

Therefore for example practical units of length.

Because you have already studies about all nine basic or fundamental quantities in SI system.

So lets begin.

## Why is Practical units measurement method is necessary ? So all the country in the world accepted this standard of units for measurement.

But why do we study this practical units.

Because  in different locations our local old units were using and we found that using this units and measurement was convenient and easy.

Whereas our practical life in SI system to express a unit we must know physics and mathematics.

So just for an example,  if  you want to take milk.

But you must know the cubic meter.

Because we measure volume in meter but when we ask the milkman for milk.

Then he reply how much liter.

Because he does not understand cubic meter.

So he know only liter and this is the volume.

Hence it should be measure in meter but milkman does not understand meter cubic.

Because he has nothing to do with physics.

But he has to sell milk and we want to buy milk.

so we made practical unit which we use in our day to day life.

### What are units in measurements?  Practical units measurement method

Then he says 10070 kg  so again ask for next truck he replay 15090 kg.

Are you observing here anything ? If not let me tell you.

Hence this seems some long number compare is not easy task.

So  make a practical unit, which will be more convenient for measurement.

Therefore a new unit ton is made.

which is use for this type huge mass measurement.

So you may be thinking,  how we converted 1000 kg for one ton.

Now for other example, You know that  we generally fill grain in sack.

Hence customers come and ask normally.

What rate you are selling ?

Then after that seller told 15 rupees kg.

Then still you have to calculate using kg system .

So to avoid this made an another practical unit.

Which is called quintal and it is define as 100 kg equal to one quintal.

Hence we fixed 100 kg in a sack, so it become again easy and convenient for our measurements purpose.

Now i hope you have well understood, why practical units measurement is necessary ?

Also check out basic system of units measurement concept.

## Practical Units Of Length

Well, just think if you want to measure a very very long length, then what you will do for this.

Because for very long length measurements you have to add so many thousand, lakh, crore meter.

So for this you have to make a practical units of length, which can measure the longest length easily.

So just for example, if  you want to measure distance from the Earth to  the Sun.

As well as the Sun to other planets like Mercury, Mars, Jupiter and many more.

So just think what you will do, if you are thinking to use to measure in SI system.

But it will be a very very big number more complex.

Therefore  for that we made a new practical units of length for easy and convenient length measurement.

But the important question is how we made unit for this type of length measurement.

So do you want to know the fact ?

Well,  we again made a unit for distance from the Earth to the Sun.

And this is called, Astronomical unit and is denoted by A.U.

Now this astronomical unit is distance from the Earth to the Sun and is called one A.U.

So what is benefit of this practical units of length ?

Therefore the main benefit is,  it became easy to compare the distance of other planet from this A.U unit.

Now it is define as the mean distance between the Earth and the Sun one A.U.

But why mean distance is taken, because the Earth rotate about the Sun and  its path is elliptical not circular.

So its mean distance is taken,  But  we don’t know A.U, whereas  we know SI unit meter.

So again one A.U is equal to 1.496*10^11 meter and it is approx to 1.5*10^11 meter length till date.

### Practical Units In Physics

So we were study about our planets only but when our astronomy developed then we started to study about stars.

Now for star distance measurement from the Earth we made another practical unit, why because in A.U measurement its number will be very big digit in lakh.

And crore so we made another unit light year to measure the distance from the Earth to the Stars year is a unit of time.

But light year is a unit of length or distance first we made its definition and then we calculated in meter light travels with high speed we know 3*10^8 m/s.

Because in one second light travels 3*10^8 meter, hence in one hour, one day, one month, one year and so on.

Hence it will travel many many large distance hence for one year we allow light to travel the distance and that distance is called “light year”.

So it is define as one light year is length which is travel by light in one year.

But when we see star in the universe and say that star is 10 light year distance from the Earth its mean that 10 years before that light was emitted by star and today we are seeing.

Hence how much it will be in meter it is simple calculation one light year = 3*10^8*60*60*24*365 meter that is equal to 9.46*10^15 meter now compare with A.U.

Which one is big, of course light year is big.

So it is larger unit ten thousand times hence use it for the Stars distance measurement.

But now scientist made one another unit for distance measurement between stars to stars which is know as “parsec”.

Just with the help of angle taking two line of one degree inclination we subtends angle one minute (1′) = 1^0/60, one second (1″) =  1’/60.

Because when we increase the length subtends angle will be small hence we know that angle = arc/radius now for making unit scientist fixed arc length one A.U .

And we know AU hence when one second (1″) angle subtends by AU called one “parsec”.

## All Units Of Measurement

hence it is define as one parsec is the radius of a circle at the centre of which, an arc of the circle is 1 AU long subtends.

So an angle of one second (1″) hence one parsec = 3.1*10^16 m hence parsec is largest unit for length or distance measurement.

whereas we are not using this unit in our home.

Because it is astronomical use for planet and stars but some unit we use in our home like foot, inch,cm, yard.

So we are using this unit from Britisher time so we have become some ideas about yard and feet one yard is equal to 3 feet.

But it is strongly attached with Indian market whenever we want to buy scale it is of one foot 12 inch.

Because we are making this scale from old time and till continue whenever we make room then say size of room 12 feet by 10 feet.

And we understand well the room size so foot has became practical unit similarly inch hence one inch = 0.0254 m or 2.54 cm one foot = 0.3048 m.

Again one yard = 0.9144 m one mile = 1609 m commonly use in America for air flight we use nautical mile.

Hence one nautical mile = 1852 m whatever object travel distance in air always express it distance in nautical mile.

Or when we travel distance on the Earth surface express in mile,

But now when we measure very small particle then we made another small practical unit.

For example when we study about material atom, molecules when we measured one molecule size it was equal to 10^-9 m.

So we given this name as nano hence one nano meter = 1nm = 10^-9 m we can see through naked eye up to 10^-4 m less than this like 10^-5, 10^-6 .

So we are not able to see through naked eye can’t distinguish water molecule then we use to see through microscope.

Then our unit became one micron = 10^-6 after that we made more small for atom size unit is one Angstrom.

And it is equal to 10^-10 m use for atom size measurement after that again we search in the nature for small particle 10^ -11 m, 10^-12 m, 10^-14 m

But not got any particle for this size and scientist search continue finally got 10^-15 m particle electron, proton,

Then made unit Fermi and it is equal to 10^-15 m, So why we not made 10^-20 m .

The answer is simple we have not got any particle for this size till date hence smallest particle measure by Fermi practical unit.

#### Conclusion: 