Atlearner-
April 19, 2023

March 16, 2021

But to measure in a scientific way, we need to know some basic things about measurement. So in this tutorial, we are going to discuss some basic aspects of measurement, such as

• What is measurement?

• What is the physical quantity?

• What are the fundamental quantities?

• What are the derived quantities?

• What is the unit?

• What are the fundamental units?

• What are the derived units?

• What are the systems of units in measurements?

• The CGS units

• The MKS units

• The FPS units

• Instruments for measurement

Measurement is a process that is associated with physical quantities of real-world objects, numbers, units, and various events. It is very basic in engineering, construction work, medical, or other technical fields, and can be used for almost every activity in our daily life.

Whatever we measure is called physical quantity in the language of science. To measure a physical quantity, we need two things, one is the numerical value and the other is its unit. However, in order to measure any physical quantity, we have to follow some rules.

In the process of measurement, we compare the given physical quantity with the known standard quantity of the same nature. For the measurement of a physical quantity, at first, we consider a constant quantity of the same nature as a standard and then we find the number which expresses, how many times the standard quantity is contained in the given physical quantity.

Now to know the details about this measurement we need to know about the physical quantity, its numerical value, and unit. So, if you are not familiar with physical quantities and units, then let's get first to know about all those things.

Anything that can be measured is called the physical quantity. For example, the mass and volume of an object, the density of an element, etc. But most of the things related to life we cannot measure such as - beauty, smell, taste, the hardness of the object, etc. So these are not physical quantities. These are qualitative observations that are usually observed with the senses.

Any physical quantity is expressed with a combination of a numerical value and a unit. For example, the physical quantity length can be quantified as 'n m', mass as 'n kg', and time as 'n s'. Where n is the numerical value and m, kg, and s are the units.

There are two types of Physical Quantity - Fundamental or Base Quantity and Derived Quantity.

The fundamental quantities are independent physical quantities, which help to obtain and find other physical quantities. These fundamental quantities are - length, mass, time, electric current, temperature, amount of substance, and luminous intensity.

Derived quantities are such quantities that are derived from the combination of fundamental quantities through multiplication and division only (no addition or subtraction or any other sign). For example - area, which is calculated by multiplying length by length (length × length), and volume which is length × length × length, and density which is calculated as the mass of the object divided by its volume (mass ÷ volume).

Unit is the quantity of a constant magnitude that is used to measure the magnitude of other quantities of the same nature. As in the example above, 'm' is used as the unit of a constant magnitude for length. Similarly, 'kg' is used for mass and 's' for time. But to accept any unit internationally, we need to be followed three essential conditions and these are

1. It should be possible to define the unit without ambiguity.

2. The unit should be reproducible.

3. The value of the unit should not change with space and time.

The units are of two kinds - fundamental units and derived units.

The fundamental or basic units are independent units, which help to obtain and find other units. These units can neither be changed nor can be related to any other fundamental units. For example - The units of length, mass, time, electric current, temperature, amount of substance, and luminous intensity.

Derived units are those units that depend on the fundamental units or which can be expressed in terms of the fundamental units. For example - The unit of area, volume, density, and force, etc.

In CGS unit system: The unit of area is centimeter square (cm × cm), the unit of volume is centimeter cube (cm × cm × cm), the unit of density is gram/centimeter cube {g/(cm × cm × cm)}, and the unit of force is Dyne {g × cm/( s × s)}, etc.

In SI or MKS unit system: The unit of area is meter square (m × m), the unit of volume is meter cube (m × m × m), the unit of density is kilogram/meter cube {kg/(m × m × m)}, and the unit of force is Newton {kg × m/ s × s)}, etc.

Basically, for a long time, three types of unit systems have been used all over the world. These systems of units are C.G.S (centimeter-gram-second), M.K.S (meter-kilogram-second), and F.P.S (foot-pound-second).

This is a French unit system. In this system, the unit of length is centimeter (cm), of mass is gram (g), and of time is second (s).

This system of units is also known as the metric system of units. In this system, the unit of length is meter (m), of mass is kilogram (kg), and of time is second (s).

To measure the same physical quantity in the different unit systems, many different measuring instruments have to be made for each unit system. Moreover, it is not possible to express the data obtained from different measurements in a coherent manner.

To address this problem the *International Bureau of Weights and Measures (BIPM)* recognized the only one unit system as the International System of Units. The units of the MKS system of three physical quantities (length, mass, and time) have been used in this system.

This is a British unit system. In this system, the unit of length is foot (ft), of mass is pound (lb), and of time is second (s).

Here is a brief overview of the instruments used to measure the physical quantities we discussed earlier.

So mass is often measured by measuring the weight of the objects using a weighing scale, rather than a balance scale comparing it directly with known masses.

Other important instruments for measuring temperature are thermocouples, thermistors, resistance temperature detector (RTD), pyrometer, langmuir probes (for electron temperature of a plasma), and infrared thermometers, etc.

To measure area we also use linear measuring instruments like - tape measure, ruler (to measure length and width), etc.

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