Units of Masurements.

 When ever we made some measurements in our daily lives, we need to specify the difference between one and other measurements. This measurements can be a count(for money) or measurements for length, width(breadth), height, weight, mass, time, temperature(hotness or coldness of a body), speed(of a moving object), e.t.c. After all these measurements we get back a number(s)(which can be either whole, fraction or decimal) which when these numbers are presented without any indication (of which one measure either mass, temperature, time, e.t.c) one can never distinguish.

Thanks to the units of measurements that give us the freedom to write our measurements attached with some unit or its symbol to indicate whether the measured value is for either length, mass or time.

Before we dip in to units of measurements, we have to know that these units we wanted to know are for measured quantities. As we mentioned above, length, mass, time, temperature are quantities and are all called fundamental quantities. Fundamental quantities are quantities in which other quantities are derived from or simply are just independent quantities. Other fundamental quantities include amount of substance and electric current. Apart from fundamental quantities there is also derived quantities which are quantities that depend on fundamental quantities. Example of such derived quantities are velocity, force, density, e.t.c.

Here are are fundamental quantities and their unit.

Fundamental quantities

Length: 

Attached to each measurement of length we add a unit of length which can either be in meter(m), feet(ft), inch(in), yard(yd), mile(mi), e.t.c. we can change one to each of the units. The choice of which one to use depends on how far we need to measure. To measure the length of a book we use  inches while to measure the distance between two towns we use miles.

Mass:

Attached to each measurement of mass we add a unit of mass which can be in gram(g), pound(lb), ounce(oz), tonne(t). The choice of units depends on how the object we need to measure is. To measure the mass of a bag of rice we use gram(g) while for mass of a car we use tonne(t).

Time:

Like the others for each measure of time we attach a unit of time which can be in second(s), minute(m), hour(h), day, week(wk), month, year(yr). Here,  also the choice of measuring unit depends on how long it will take to make the measurement.

Temperature:

As we already know, temperature is the measure of how hot or how cold a body or an object is. Scientists use kelvin(K), celcius(C) and fahrenheit(F) to measure the amount of temperature. To measure extreme hot we use kelvin(K) while for extreme cold we use Fahrenheit(F).

Amount of substance:

To measure amount of substance, we use mole. Mole composed of about 6.02214076×10²³ particles of either atoms, ions, molecules, electrons, e.t.c. Its short form is mol(without the 'e').

Electric current:

Electric current is the measure of quantity of charge that passes through a conductor or simply the rate of flow of charge( I=Q/t, where Q is the amount of charge and t is time taken for the amount of charge to pase). The unit of measurement for an electric current is amphere (A).

Derived quantities

From the name, derived quantities are those quantities formed using another quantities (fundamental quantities). Example of them are:

Velocity: 
Velocity is calculated using fundamental quantity length( to measure displacement) and time.
velocity (v) =  displacement/time 
The unit of velocity is m/s (read as meter per second )

Acceleration:
Like velocity, accelaration is derived from same fundamental quantities( length and time) because  Acceleration is the rate of change of velocity.
Acceleration (a) = displacement/second × second
The unit of acceleration is m/s² ( meter per second squared)

Force:
Force is derived from the combination of mass and accelaration of a body.
Force F = ma , mass is in gram and  acceleration is in m/s². So, force is measured in gm/s² or kgm/s²(known as Newton, N).


Work:
Work (W) = F × S where F is the force and S is a distance perpendicular to the direction of force. The unit of work is Ns known as Joule(J).

Power:
Power is the rate of doing work, so we derived power from work
Power P = W/t , where W is the workdone and t is the time. So the unit of power is J/s known as Watt(W).

Area:
Area = length × breadth
Unit of area is m²(meter square)

Volume:
Volume = length × breadth × height
Unit of volume is m³(meter cube)
 
Density:
Density = Mass/Volume = kg/m³
So, the unit of density is kg/m³

Pressure:
Pressure = Force/Area =  N/m²
Therefore, the unit of Pressure is N/m².

Hence, this is how derived quantities and their units are formed.

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