Very first we have to discussed about physical quantity here we study about nature in physics and nature is around us whatever object we see and interact with this we see in nature different object have different characteristics.Each and every component of nature having different characteristics like chock, board, light,earth, air, water many more each and every component we sense around nature.
Now we will nomenclature the physical quantity for measurement according to their characteristics example when we take a chock it easily confined in my fist but when we take a long stick it is not confined in fist so for this characteristics measurement we use length and latter this length will be use in many places like distance, height, width, thickness,volume in all places length will be use.now we will see other characteristics of nature take example we will take same length of two object in our both hand in left hand take a chock and in right hand take iron rod then we observe that in left hand chock pushes my hand less but right hand iron rod pushes my hand more whereas length of both object is same so this is other characteristics rather than length hence we nomenclature this natural characteristics mass so in similar fashion we observed more natural characteristics and nomenclature means putting their name and this is called physical quantity. hence we observed in nature and start to making characteristics 1,2,3,4,5,7,8,,9,10,……..100000 lakh of characteristics now it become problem for us shortage of name also it become difficult to remember name of each characteristics and its properties then we started to think over this characteristics if there should be only one characteristics then it will be good for us to study scientist tried to make a single characteristics through which all the other characteristics can be explain when we taken same length of chock and iron rod and try to explain through single characteristics length but it fail because length is same but pushing characteristics of both object is different hence there must be a another characteristics and it was nomenclature as mass hence if one quantity is not able to explain other characteristics then we have to consider another quantity. take an example length, width, height tell me these three are different characteristics or same characteristics wait this is same one quantity can explain these three characteristics when length is rotated with 90 degree it become height now length is again rotated with 90 degree it become width so our basic quantity is length through which we measure characteristics of physical quantity length.now using length technique measurement we can measure width and height no separate technique required to measure width and height.now i ask you that in the evening you had gone to your friend home how much distance is your friend home this is another quantity which is present in nature now we need to study this distance characteristics and it will be a new quantity big no because distance is also length between two point and we have already basic quantity length for measurement now take another question when i ask you what is speed of your motorcycle you reply 20 m/s here motorcycle is new component of nature and speed is its characteristics this is another new quantity ? big no because it is define m/s that is length per unit time so we see here height, width, distance, speed, volume in all these measurement we are measuring length all these quantities having same characteristics which is length basic physical quantity. how easy it become you learn one technique length measurement and measuring all above quantity on the basis of this we made two group one is Fundamental/ basic quantity and other is derived quantity. hence length is fundamental quantity and derived quantity from length are width, height, distance, area, volume, speed and many more which involve length.so we can say that in the world there is only one basic quantity length our answer is big no just above we have seen mass where length fail to explain chock and iron rod characteristics so we can’t explain length in terms of mass and similarly mass in terms of length so these two are separate basic quantity. hence we know heavy mass body has more pushing characteristics so from mass derived quantity are force we know force depend upon mass, momentum, energy. now we learned basic quantity through which we will measure characteristics of the nature and are happy but wait a boy came to ask a physics question we simply told him today we have learnt basic quantity please come tomorrow another boy came to ask question again told you come after two days, third boy came to ask question again told him you came after one week now what is this can we measure the length first boy will come, can we explain with mass no then what is this new characteristics we say everyday after 24 hr sun arises.hence we nomenclature this new basic quantity time. so time is that quantity which can not be express by length and mass. so our third new basic quantity is time similarly temperature which can’t be express by length, mass, time so after observing all the characteristics of the nature we finally found seven Fundamental/Basic quantities hence these are seven fundamental quantities length, mass, time, temperature, electric current, amount of substance, luminous intensity, plane angle, solid angle (plan and solid angle are supplementary added latter ).
Why we want to measure Physical quantity ?
Nature is a science of measurement nature is all about measurement how we say today is hotter on the basis of measurement two friend are discussing one say today is hotter and other say yesterday was hotter no one is agree to accept then go to third person and ask yesterday was hotter or today is hotter then third person measure temperature and say yesterday temperature was 45 degree Celsius today is 50 degree Celsius then they agreed otherwise fighting continue so science is measurement take an another example of land two person are fighting one say my land is from this pillar to 10th pillar other say 10th number pillar is in my land then what is solution measurement so physics is all about measurement which measurement nature because physics is study of nature what we want to measure characteristics so finally we measure nature characteristics.
Now how we will measure any physical quantity ? we will have to make a unique system.
Unit measurement of a quantity is a standard measurement which is given a particular name its value should not change with time, place and other physical conditions.Now we will apply unit we know that a physical quantity length use to measure size all scientist sit together and decided that stretch your hand and cut a iron rod length of your hand and nomenclature this one meter again cut 50 iron rod of this size and distributed in every country for measurement named one meter and hang one sample in lab. now every country has got a iron rod length one meter now again the country will make more iron rod of same length and distributed in all city and announce that this length is one meter from this we will use for measurement of one meter written on this iron rod whole over the world our unit of length is ready now for us this became a standard for meter wait but as the season changes in summer this iron rod length increase by some length and in winter it become some shorter then it created problem among people and lead to continue fighting so for this reason our standard should be like that it should not depend upon season, location and any physical condition then it will be a standard unit hence what are characteristics of a standard unit, value should not change with time,should not destroyed with time in case of iron rod after time passes it get to rust and after cleaning it became smaller. it must be well defined its definition should be so accurate so that any other can’t create controversy on its definition an example we made a standard that when ice is converted to water and water is converted to ice that temperature is zero degree but a person claim on this when we increase the pressure and decreases the pressure it become ice before and after zero degree temperature now it not a standard then we again correct our definition that when water converted to ice its pressure should be normal at sea level now it became standard so any type of confusion should not create upon standard unit. take an example when we talk about light speed and its frequency which light color we consider because light every color frequency is different then we mention that orange color we are considering so in this manner our definition should be clear so in science we always correction required and changes take place. standard unit must be reproduce whenever needed easily means to say that suppose earth quack happen and lost our meter length then again it should be created easily that should be unit standard.next point should be proper size neither to big nor too short now it is very interesting we have to made mass unit how we will choose the standard unit suppose all people giving their opinion some given small size mass next given larger than this other given larger than this and so on then how we will choose the standard unit of mass how much big mass want to make unit, what is unit means one ? now we think over it we will make unit of that mass which comes in our daily use so that there can not involve too much mathematical calculation we made the mass unit kilogram then how much mass will be one kilogram how we will decide one kilogram mass then we started to search daily use of our life that daily food daily we go to market and brought vegetable how much vegetable daily brought from market for a normal family daily brought one kg vegetable so what most we do measurement daily that is our food so we fixed the mass which we use daily buy then we fixed that mass one kg then it became one kg in the world. now for big mass we compare from our standard unit one kg like 5kg five times of one kg for 10 kg we use ten times of one kg and so on suppose if kg was not our unit some other unit were there then how we told buy vegetable told shopkeeper give me 500 unit vegetable, give me 1000 unit vegetable and so on it was awkward now it seen it is ok for daily life necessity but when we brought material from outside to truck it is how many of kg 100 kg, 1000 kg, 10000 kg so it become also awkward then we again change for heavy mass name and nomenclature 1000 kg approx one tons now it became easy 1, 2, 3, 4,……20 tons for truck so for the sake of simplicity change the unit. now we got to buy gold then we can’t say shopkeeper give me .0012 kg of gold this is some awkward so again change this unit to milligram and easily say 5 mg , 10 mg, 50 mg unit change for our simplicity so important point for unit is of proper size wherever we use similar for liquid we fixed litter but when more quantity of water taken they we say i want 5 bucket of water now our unit is bucket so it became practical unit should be proper size of measurement so when i say what will be mass of the sun if you calculate in kg it will be a very large number not easy to told then there should be a big unit for sun mass similarly for distance also distance from sun to earth if we measure in meter it will be very difficult to told here should be a big unit for length that is light year so every unit has standard and practical unit both now i hope we have understand clearly about unit we will continue for measurement in next post.
Thanks for reading Basic Units and Measurement concept